patch, 5 partsCreate 'feature.*' config area and some centralized config parsing

builtin/update-index.c, config.c, read-cache.c, repo-settings.c, repo-settings.h

diff --git a/builtin/update-index.c b/builtin/update-index.c
index dff2f4b837..6c26bbae80 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -18,6 +18,7 @@
 #include "dir.h"
 #include "split-index.h"
 #include "fsmonitor.h"
+#include "repo-settings.h"
 
 /*
  * Default to not allowing changes to the list of files. The
@@ -966,6 +967,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	struct parse_opt_ctx_t ctx;
 	strbuf_getline_fn getline_fn;
 	int parseopt_state = PARSE_OPT_UNKNOWN;
+	struct repository *r = the_repository;
 	struct option options[] = {
 		OPT_BIT('q', NULL, &refresh_args.flags,
 			N_("continue refresh even when index needs update"),
@@ -1180,11 +1182,12 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		remove_split_index(&the_index);
 	}
 
+	prepare_repo_settings(r);
 	switch (untracked_cache) {
 	case UC_UNSPECIFIED:
 		break;
 	case UC_DISABLE:
-		if (git_config_get_untracked_cache() == 1)
+		if (r->settings->core_untracked_cache & CORE_UNTRACKED_CACHE_WRITE)
 			warning(_("core.untrackedCache is set to true; "
 				  "remove or change it, if you really want to "
 				  "disable the untracked cache"));
@@ -1196,7 +1199,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		return !test_if_untracked_cache_is_supported();
 	case UC_ENABLE:
 	case UC_FORCE:
-		if (git_config_get_untracked_cache() == 0)
+		if (r->settings->core_untracked_cache == 0)
 			warning(_("core.untrackedCache is set to false; "
 				  "remove or change it, if you really want to "
 				  "enable the untracked cache"));
diff --git a/config.c b/config.c
index faa57e436c..3241dbc54d 100644
--- a/config.c
+++ b/config.c
@@ -2277,30 +2277,6 @@ int git_config_get_expiry_in_days(const char *key, timestamp_t *expiry, timestam
 	return -1; /* thing exists but cannot be parsed */
 }
 
-int git_config_get_untracked_cache(void)
-{
-	int val = -1;
-	const char *v;
-
-	/* Hack for test programs like test-dump-untracked-cache */
-	if (ignore_untracked_cache_config)
-		return -1;
-
-	if (!git_config_get_maybe_bool("core.untrackedcache", &val))
-		return val;
-
-	if (!git_config_get_value("core.untrackedcache", &v)) {
-		if (!strcasecmp(v, "keep"))
-			return -1;
-
-		error(_("unknown core.untrackedCache value '%s'; "
-			"using 'keep' default value"), v);
-		return -1;
-	}
-
-	return -1; /* default value */
-}
-
 int git_config_get_split_index(void)
 {
 	int val;
diff --git a/read-cache.c b/read-cache.c
index ee1aaa8917..e67e6f6e3e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1846,18 +1846,17 @@ static void check_ce_order(struct index_state *istate)
 
 static void tweak_untracked_cache(struct index_state *istate)
 {
-	switch (git_config_get_untracked_cache()) {
-	case -1: /* keep: do nothing */
-		break;
-	case 0: /* false */
+	struct repository *r = the_repository;
+
+	prepare_repo_settings(r);
+
+	if (!(r->settings->core_untracked_cache & CORE_UNTRACKED_CACHE_KEEP)) {
 		remove_untracked_cache(istate);
-		break;
-	case 1: /* true */
-		add_untracked_cache(istate);
-		break;
-	default: /* unknown value: do nothing */
-		break;
+		return;
 	}
+
+	if (r->settings->core_untracked_cache & CORE_UNTRACKED_CACHE_WRITE)
+		add_untracked_cache(istate);
 }
 
 static void tweak_split_index(struct index_state *istate)
diff --git a/repo-settings.c b/repo-settings.c
index f328602fd7..807c5a29d6 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -30,6 +30,20 @@ static int git_repo_config(const char *key, const char *value, void *cb)
 		rs->index_version = git_config_int(key, value);
 		return 0;
 	}
+	if (!strcmp(key, "core.untrackedcache")) {
+		int bool_value = git_parse_maybe_bool(value);
+		if (bool_value == 0)
+			rs->core_untracked_cache = 0;
+		else if (bool_value == 1)
+			rs->core_untracked_cache = CORE_UNTRACKED_CACHE_KEEP |
+						   CORE_UNTRACKED_CACHE_WRITE;
+		else if (!strcasecmp(value, "keep"))
+			rs->core_untracked_cache = CORE_UNTRACKED_CACHE_KEEP;
+		else
+			error(_("unknown core.untrackedCache value '%s'; "
+				"using 'keep' default value"), value);
+		return 0;
+	}
 
 	return 1;
 }
@@ -46,6 +60,13 @@ void prepare_repo_settings(struct repository *r)
 	r->settings->gc_write_commit_graph = -1;
 	r->settings->pack_use_sparse = -1;
 	r->settings->index_version = -1;
+	r->settings->core_untracked_cache = -1;
 
 	repo_config(r, git_repo_config, r->settings);
+
+	/* Hack for test programs like test-dump-untracked-cache */
+	if (ignore_untracked_cache_config)
+		r->settings->core_untracked_cache = CORE_UNTRACKED_CACHE_KEEP;
+	else
+		UPDATE_DEFAULT(r->settings->core_untracked_cache, CORE_UNTRACKED_CACHE_KEEP);
 }
diff --git a/repo-settings.h b/repo-settings.h
index 1151c2193a..bac9b87d49 100644
--- a/repo-settings.h
+++ b/repo-settings.h
@@ -1,11 +1,15 @@
 #ifndef REPO_SETTINGS_H
 #define REPO_SETTINGS_H
 
+#define CORE_UNTRACKED_CACHE_WRITE (1 << 0)
+#define CORE_UNTRACKED_CACHE_KEEP (1 << 1)
+
 struct repo_settings {
 	int core_commit_graph;
 	int gc_write_commit_graph;
 	int pack_use_sparse;
 	int index_version;
+	int core_untracked_cache;
 };
 
 struct repository;

Documentation/config.txt, Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/gc.txt, repo-settings.c

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e3f5bc3396..77f3b1486b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -345,6 +345,8 @@ include::config/difftool.txt[]
 
 include::config/fastimport.txt[]
 
+include::config/feature.txt[]
+
 include::config/fetch.txt[]
 
 include::config/format.txt[]
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 75538d27e7..d80162681a 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -577,7 +577,8 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to false, unless
+	`feature.manyCommits` is enabled. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
new file mode 100644
index 0000000000..f74314ae90
--- /dev/null
+++ b/Documentation/config/feature.txt
@@ -0,0 +1,15 @@
+feature.*::
+	The config settings that start with `feature.` modify the defaults of
+	a group of other config settings. These groups are created by the Git
+	developer community as recommended defaults and are subject to change.
+	In particular, new config options may be added with different defaults.
+
+feature.manyCommits::
+	Enable config options that optimize for repos with many commits. This
+	setting is recommended for repos with at least 100,000 commits. The
+	new default values are:
++
+* `core.commitGraph=true` enables reading the commit-graph file.
++
+* `gc.writeCommitGraph=true` enables writing the commit-graph file during
+garbage collection.
\ No newline at end of file
diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 02b92b18b5..31a5fc4f75 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -63,8 +63,8 @@ gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
 	linkgit:git-gc[1] is run. When using `git gc --auto`
 	the commit-graph will be updated if housekeeping is
-	required. Default is false. See linkgit:git-commit-graph[1]
-	for details.
+	required. Default is false, unless `feature.manyCommits`
+	is enabled. See linkgit:git-commit-graph[1] for details.
 
 gc.logExpiry::
 	If the file gc.log exists, then `git gc --auto` will print
diff --git a/repo-settings.c b/repo-settings.c
index 13a9128f62..f328602fd7 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -3,10 +3,17 @@
 #include "config.h"
 #include "repo-settings.h"
 
+#define UPDATE_DEFAULT(s,v) do { if (s == -1) { s = v; } } while(0)
+
 static int git_repo_config(const char *key, const char *value, void *cb)
 {
 	struct repo_settings *rs = (struct repo_settings *)cb;
 
+	if (!strcmp(key, "feature.manycommits")) {
+		UPDATE_DEFAULT(rs->core_commit_graph, 1);
+		UPDATE_DEFAULT(rs->gc_write_commit_graph, 1);
+		return 0;
+	}
 	if (!strcmp(key, "core.commitgraph")) {
 		rs->core_commit_graph = git_config_bool(key, value);
 		return 0;

Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/index.txt, repo-settings.c, t/t1600-index.sh

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index d80162681a..7a2a33bc8c 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -86,7 +86,9 @@ core.untrackedCache::
 	it will automatically be removed, if set to `false`. Before
 	setting it to `true`, you should check that mtime is working
 	properly on your system.
-	See linkgit:git-update-index[1]. `keep` by default.
+	See linkgit:git-update-index[1]. `keep` by default, unless
+	`feature.manyFiles` is enabled which sets this setting to
+	`true` by default.
 
 core.checkStat::
 	When missing or is set to `default`, many fields in the stat
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index f74314ae90..c2d9ef7473 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -12,4 +12,14 @@ feature.manyCommits::
 * `core.commitGraph=true` enables reading the commit-graph file.
 +
 * `gc.writeCommitGraph=true` enables writing the commit-graph file during
-garbage collection.
\ No newline at end of file
+garbage collection.
+
+feature.manyFiles::
+	Enable config options that optimize for repos with many files in the
+	working directory. With many files, commands such as `git status` and
+	`git checkout` may be slow and these new defaults improve performance:
++
+* `index.version=4` enables path-prefix compression in the index.
++
+* `core.untrackedCache=true` enables the untracked cache. This setting assumes
+that mtime is working on your machine.
\ No newline at end of file
diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
index f181503041..7cb50b37e9 100644
--- a/Documentation/config/index.txt
+++ b/Documentation/config/index.txt
@@ -24,3 +24,4 @@ index.threads::
 index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.
+	If `feature.manyFiles` is enabled, then the default is 4.
diff --git a/repo-settings.c b/repo-settings.c
index 807c5a29d6..9e4b8e6268 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -14,6 +14,12 @@ static int git_repo_config(const char *key, const char *value, void *cb)
 		UPDATE_DEFAULT(rs->gc_write_commit_graph, 1);
 		return 0;
 	}
+	if (!strcmp(key, "feature.manyfiles")) {
+		UPDATE_DEFAULT(rs->index_version, 4);
+		UPDATE_DEFAULT(rs->core_untracked_cache,
+			       CORE_UNTRACKED_CACHE_KEEP | CORE_UNTRACKED_CACHE_WRITE);
+		return 0;
+	}
 	if (!strcmp(key, "core.commitgraph")) {
 		rs->core_commit_graph = git_config_bool(key, value);
 		return 0;
diff --git a/t/t1600-index.sh b/t/t1600-index.sh
index 42962ed7d4..c77721b580 100755
--- a/t/t1600-index.sh
+++ b/t/t1600-index.sh
@@ -59,17 +59,38 @@ test_expect_success 'out of bounds index.version issues warning' '
 	)
 '
 
-test_expect_success 'GIT_INDEX_VERSION takes precedence over config' '
+test_index_version () {
+	INDEX_VERSION_CONFIG=$1 &&
+	FEATURE_MANY_FILES=$2 &&
+	ENV_VAR_VERSION=$3
+	EXPECTED_OUTPUT_VERSION=$4 &&
 	(
 		rm -f .git/index &&
-		GIT_INDEX_VERSION=4 &&
-		export GIT_INDEX_VERSION &&
-		git config --add index.version 2 &&
+		rm -f .git/config &&
+		if test "$INDEX_VERSION_CONFIG" -ne 0
+		then
+			git config --add index.version $INDEX_VERSION_CONFIG
+		fi &&
+		git config --add feature.manyFiles $FEATURE_MANY_FILES
+		if test "$ENV_VAR_VERSION" -ne 0
+		then
+			GIT_INDEX_VERSION=$ENV_VAR_VERSION &&
+			export GIT_INDEX_VERSION
+		else
+			unset GIT_INDEX_VERSION
+		fi &&
 		git add a 2>&1 &&
-		echo 4 >expect &&
+		echo $EXPECTED_OUTPUT_VERSION >expect &&
 		test-tool index-version <.git/index >actual &&
 		test_cmp expect actual
 	)
+}
+
+test_expect_success 'index version config precedence' '
+	test_index_version 2 false 4 4 &&
+	test_index_version 2 true 0 2 &&
+	test_index_version 0 true 0 4 &&
+	test_index_version 0 true 2 2
 '
 
 test_done

Makefile, builtin/gc.c, builtin/pack-objects.c, commit-graph.c, read-cache.c, repo-settings.c, repo-settings.h, repository.h

diff --git a/Makefile b/Makefile
index 11ccea4071..032fe9b5f9 100644
--- a/Makefile
+++ b/Makefile
@@ -964,6 +964,7 @@ LIB_OBJS += refspec.o
 LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace-object.o
+LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
 LIB_OBJS += resolve-undo.o
diff --git a/builtin/gc.c b/builtin/gc.c
index c18efadda5..243be2907b 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -27,6 +27,7 @@
 #include "pack-objects.h"
 #include "blob.h"
 #include "tree.h"
+#include "repo-settings.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -41,7 +42,6 @@ static int aggressive_depth = 50;
 static int aggressive_window = 250;
 static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
-static int gc_write_commit_graph;
 static int detach_auto = 1;
 static timestamp_t gc_log_expire_time;
 static const char *gc_log_expire = "1.day.ago";
@@ -148,7 +148,6 @@ static void gc_config(void)
 	git_config_get_int("gc.aggressivedepth", &aggressive_depth);
 	git_config_get_int("gc.auto", &gc_auto_threshold);
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
-	git_config_get_bool("gc.writecommitgraph", &gc_write_commit_graph);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_get_expiry("gc.pruneexpire", &prune_expire);
 	git_config_get_expiry("gc.worktreepruneexpire", &prune_worktrees_expire);
@@ -685,11 +684,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		clean_pack_garbage();
 	}
 
-	if (gc_write_commit_graph &&
-	    write_commit_graph_reachable(get_object_directory(),
-					 !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
-					 NULL))
-		return 1;
+	prepare_repo_settings(the_repository);
+	if (the_repository->settings->gc_write_commit_graph == 1)
+		write_commit_graph_reachable(get_object_directory(),
+					     !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
+					     NULL);
 
 	if (auto_gc && too_many_loose_objects())
 		warning(_("There are too many unreachable loose objects; "
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 267c562b1f..223038b309 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -34,6 +34,7 @@
 #include "dir.h"
 #include "midx.h"
 #include "trace2.h"
+#include "repo-settings.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -2709,10 +2710,6 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(k, "pack.usesparse")) {
-		sparse = git_config_bool(k, v);
-		return 0;
-	}
 	if (!strcmp(k, "pack.threads")) {
 		delta_search_threads = git_config_int(k, v);
 		if (delta_search_threads < 0)
@@ -3332,6 +3329,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	read_replace_refs = 0;
 
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
+	prepare_repo_settings(the_repository);
+	if (!sparse && the_repository->settings->pack_use_sparse != -1)
+		sparse = the_repository->settings->pack_use_sparse;
+
 	reset_pack_idx_option(&pack_idx_opts);
 	git_config(git_pack_config, NULL);
 
diff --git a/commit-graph.c b/commit-graph.c
index b3c4de79b6..48e03aa285 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -16,6 +16,7 @@
 #include "hashmap.h"
 #include "replace-object.h"
 #include "progress.h"
+#include "repo-settings.h"
 
 #define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
 #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
@@ -466,7 +467,6 @@ static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
 static int prepare_commit_graph(struct repository *r)
 {
 	struct object_directory *odb;
-	int config_value;
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
 		die("dying as requested by the '%s' variable on commit-graph load!",
@@ -476,9 +476,10 @@ static int prepare_commit_graph(struct repository *r)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
+	prepare_repo_settings(r);
+
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
-	    (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
-	    !config_value))
+	    r->settings->core_commit_graph != 1)
 		/*
 		 * This repository is not configured to use commit graphs, so
 		 * do not load one. (But report commit_graph_attempted anyway
diff --git a/read-cache.c b/read-cache.c
index c701f7f8b8..ee1aaa8917 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -25,6 +25,7 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "repo-settings.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -1599,16 +1600,17 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
 
 #define INDEX_FORMAT_DEFAULT 3
 
-static unsigned int get_index_format_default(void)
+static unsigned int get_index_format_default(struct repository *r)
 {
 	char *envversion = getenv("GIT_INDEX_VERSION");
 	char *endp;
-	int value;
 	unsigned int version = INDEX_FORMAT_DEFAULT;
 
 	if (!envversion) {
-		if (!git_config_get_int("index.version", &value))
-			version = value;
+		prepare_repo_settings(r);
+
+		if (r->settings->index_version >= 0)
+			version = r->settings->index_version;
 		if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
 			warning(_("index.version set, but the value is invalid.\n"
 				  "Using version %i"), INDEX_FORMAT_DEFAULT);
@@ -2765,7 +2767,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	}
 
 	if (!istate->version) {
-		istate->version = get_index_format_default();
+		istate->version = get_index_format_default(the_repository);
 		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}
diff --git a/repo-settings.c b/repo-settings.c
new file mode 100644
index 0000000000..13a9128f62
--- /dev/null
+++ b/repo-settings.c
@@ -0,0 +1,44 @@
+#include "cache.h"
+#include "repository.h"
+#include "config.h"
+#include "repo-settings.h"
+
+static int git_repo_config(const char *key, const char *value, void *cb)
+{
+	struct repo_settings *rs = (struct repo_settings *)cb;
+
+	if (!strcmp(key, "core.commitgraph")) {
+		rs->core_commit_graph = git_config_bool(key, value);
+		return 0;
+	}
+	if (!strcmp(key, "gc.writecommitgraph")) {
+		rs->gc_write_commit_graph = git_config_bool(key, value);
+		return 0;
+	}
+	if (!strcmp(key, "pack.usesparse")) {
+		rs->pack_use_sparse = git_config_bool(key, value);
+		return 0;
+	}
+	if (!strcmp(key, "index.version")) {
+		rs->index_version = git_config_int(key, value);
+		return 0;
+	}
+
+	return 1;
+}
+
+void prepare_repo_settings(struct repository *r)
+{
+	if (r->settings)
+		return;
+
+	r->settings = xmalloc(sizeof(*r->settings));
+
+	/* Defaults */
+	r->settings->core_commit_graph = -1;
+	r->settings->gc_write_commit_graph = -1;
+	r->settings->pack_use_sparse = -1;
+	r->settings->index_version = -1;
+
+	repo_config(r, git_repo_config, r->settings);
+}
diff --git a/repo-settings.h b/repo-settings.h
new file mode 100644
index 0000000000..1151c2193a
--- /dev/null
+++ b/repo-settings.h
@@ -0,0 +1,15 @@
+#ifndef REPO_SETTINGS_H
+#define REPO_SETTINGS_H
+
+struct repo_settings {
+	int core_commit_graph;
+	int gc_write_commit_graph;
+	int pack_use_sparse;
+	int index_version;
+};
+
+struct repository;
+
+void prepare_repo_settings(struct repository *r);
+
+#endif /* REPO_SETTINGS_H */
diff --git a/repository.h b/repository.h
index 4fb6a5885f..352afc9cd8 100644
--- a/repository.h
+++ b/repository.h
@@ -4,6 +4,7 @@
 #include "path.h"
 
 struct config_set;
+struct repo_settings;
 struct git_hash_algo;
 struct index_state;
 struct lock_file;
@@ -72,6 +73,8 @@ struct repository {
 	 */
 	char *submodule_prefix;
 
+	struct repo_settings *settings;
+
 	/* Subsystems */
 	/*
 	 * Repository's config which contains key-value pairs from the usual

Documentation/config/feature.txt, Documentation/config/fetch.txt, Documentation/config/merge.txt, Documentation/config/pack.txt, builtin/am.c, fetch-negotiator.c, fetch-negotiator.h, fetch-pack.c, merge-recursive.c, merge-recursive.h, repo-settings.c, repo-settings.h, t/t5552-skipping-fetch-negotiator.sh

diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index c2d9ef7473..287621b1e8 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -4,6 +4,23 @@ feature.*::
 	developer community as recommended defaults and are subject to change.
 	In particular, new config options may be added with different defaults.
 
+feature.experimental::
+	Enable config options that are new to Git, and are being considered for
+	future defaults. Config settings included here may be added or removed
+	with each release, including minor version updates. These settings may
+	have unintended interactions since they are so new. Please enable this
+	setting if you are interested in providing feedback on experimental
+	features. The new default values are:
++
+* `pack.useSparse=true` uses a new algorithm when constructing a pack-file
+which can improve `git push` performance in repos with many files.
++
+* `merge.directoryRenames=true` uses a new algorithm for detecting renames by
+using entire directories at a time instead of single files at a time.
++
+* `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
+skipping more commits at a time, reducing the number of round trips.
+
 feature.manyCommits::
 	Enable config options that optimize for repos with many commits. This
 	setting is recommended for repos with at least 100,000 commits. The
diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
index ba890b5884..d402110638 100644
--- a/Documentation/config/fetch.txt
+++ b/Documentation/config/fetch.txt
@@ -59,7 +59,8 @@ fetch.negotiationAlgorithm::
 	effort to converge faster, but may result in a larger-than-necessary
 	packfile; The default is "default" which instructs Git to use the default algorithm
 	that never skips commits (unless the server has acknowledged it or one
-	of its descendants).
+	of its descendants). If `feature.experimental` is enabled, then this
+	setting defaults to "skipping".
 	Unknown values will cause 'git fetch' to error out.
 +
 See also the `--negotiation-tip` option for linkgit:git-fetch[1].
diff --git a/Documentation/config/merge.txt b/Documentation/config/merge.txt
index 6a313937f8..e8def2d63c 100644
--- a/Documentation/config/merge.txt
+++ b/Documentation/config/merge.txt
@@ -54,7 +54,8 @@ merge.directoryRenames::
 	moved into the new directory.  If set to "conflict", a conflict
 	will be reported for such paths.  If merge.renames is false,
 	merge.directoryRenames is ignored and treated as false.  Defaults
-	to "conflict".
+	to "conflict" unless `feature.experimental` is enabled and the
+	default is "true".
 
 merge.renormalize::
 	Tell Git that canonical representation of files in the
diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index 9cdcfa7324..1d66f0c992 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -112,7 +112,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames.
+	commits contain certain types of direct renames. Default is `false`
+	unless `feature.experimental` is enabled.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.
diff --git a/builtin/am.c b/builtin/am.c
index 1aea657a7f..5f3ee3e6cd 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -34,6 +34,7 @@
 #include "string-list.h"
 #include "packfile.h"
 #include "repository.h"
+#include "repo-settings.h"
 
 /**
  * Returns the length of the first line of msg.
@@ -1538,7 +1539,8 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
 	o.branch1 = "HEAD";
 	their_tree_name = xstrfmt("%.*s", linelen(state->msg), state->msg);
 	o.branch2 = their_tree_name;
-	o.detect_directory_renames = 0;
+	prepare_repo_settings(the_repository);
+	the_repository->settings->merge_directory_renames = 0;
 
 	if (state->quiet)
 		o.verbosity = 0;
diff --git a/fetch-negotiator.c b/fetch-negotiator.c
index d6d685cba0..e2990cf46e 100644
--- a/fetch-negotiator.c
+++ b/fetch-negotiator.c
@@ -2,19 +2,21 @@
 #include "fetch-negotiator.h"
 #include "negotiator/default.h"
 #include "negotiator/skipping.h"
+#include "repository.h"
+#include "repo-settings.h"
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm)
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator)
 {
-	if (algorithm) {
-		if (!strcmp(algorithm, "skipping")) {
-			skipping_negotiator_init(negotiator);
-			return;
-		} else if (!strcmp(algorithm, "default")) {
-			/* Fall through to default initialization */
-		} else {
-			die("unknown fetch negotiation algorithm '%s'", algorithm);
-		}
+	prepare_repo_settings(r);
+	switch(r->settings->fetch_negotiation_algorithm) {
+	case FETCH_NEGOTIATION_SKIPPING:
+		skipping_negotiator_init(negotiator);
+		return;
+
+	case FETCH_NEGOTIATION_DEFAULT:
+	default:
+		default_negotiator_init(negotiator);
+		return;
 	}
-	default_negotiator_init(negotiator);
 }
diff --git a/fetch-negotiator.h b/fetch-negotiator.h
index 9e3967ce66..ea78868504 100644
--- a/fetch-negotiator.h
+++ b/fetch-negotiator.h
@@ -2,6 +2,7 @@
 #define FETCH_NEGOTIATOR_H
 
 struct commit;
+struct repository;
 
 /*
  * An object that supplies the information needed to negotiate the contents of
@@ -52,7 +53,7 @@ struct fetch_negotiator {
 	void *data;
 };
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm);
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator);
 
 #endif
diff --git a/fetch-pack.c b/fetch-pack.c
index 65be043f2a..d81f47c07b 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -36,7 +36,6 @@ static int agent_supported;
 static int server_supports_filtering;
 static struct lock_file shallow_lock;
 static const char *alternate_shallow_file;
-static char *negotiation_algorithm;
 static struct strbuf fsck_msg_types = STRBUF_INIT;
 
 /* Remember to update object flag allocation in object.h */
@@ -892,12 +891,13 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 				 struct shallow_info *si,
 				 char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	struct object_id oid;
 	const char *agent_feature;
 	int agent_len;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 
 	sort_ref_list(&ref, ref_compare_name);
 	QSORT(sought, nr_sought, cmp_ref_by_name);
@@ -911,7 +911,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 
 	if (server_supports("shallow"))
 		print_verbose(args, _("Server supports %s"), "shallow");
-	else if (args->depth > 0 || is_repository_shallow(the_repository))
+	else if (args->depth > 0 || is_repository_shallow(r))
 		die(_("Server does not support shallow clients"));
 	if (args->depth > 0 || args->deepen_since || args->deepen_not)
 		args->deepen = 1;
@@ -1379,6 +1379,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				    struct shallow_info *si,
 				    char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	enum fetch_state state = FETCH_CHECK_LOCAL;
 	struct oidset common = OIDSET_INIT;
@@ -1386,7 +1387,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	int in_vain = 0;
 	int haves_to_send = INITIAL_FLUSH;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 	packet_reader_init(&reader, fd[0], NULL, 0,
 			   PACKET_READ_CHOMP_NEWLINE |
 			   PACKET_READ_DIE_ON_ERR_PACKET);
@@ -1505,8 +1506,6 @@ static void fetch_pack_config(void)
 	git_config_get_bool("repack.usedeltabaseoffset", &prefer_ofs_delta);
 	git_config_get_bool("fetch.fsckobjects", &fetch_fsck_objects);
 	git_config_get_bool("transfer.fsckobjects", &transfer_fsck_objects);
-	git_config_get_string("fetch.negotiationalgorithm",
-			      &negotiation_algorithm);
 
 	git_config(fetch_pack_config_cb, NULL);
 }
diff --git a/merge-recursive.c b/merge-recursive.c
index 12300131fc..162d5a4753 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -28,6 +28,7 @@
 #include "submodule.h"
 #include "revision.h"
 #include "commit-reach.h"
+#include "repo-settings.h"
 
 struct path_hashmap_entry {
 	struct hashmap_entry e;
@@ -1375,10 +1376,14 @@ static int handle_rename_via_dir(struct merge_options *opt,
 	 * there is no content merge to do; just move the file into the
 	 * desired final location.
 	 */
+	struct repository *r = the_repository;
 	const struct rename *ren = ci->ren1;
 	const struct diff_filespec *dest = ren->pair->two;
 	char *file_path = dest->path;
-	int mark_conflicted = (opt->detect_directory_renames == 1);
+	int mark_conflicted;
+
+	prepare_repo_settings(r);
+	mark_conflicted = (r->settings->merge_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT);
 	assert(ren->dir_rename_original_dest);
 
 	if (!opt->call_depth && would_lose_untracked(opt, dest->path)) {
@@ -2850,6 +2855,7 @@ static int detect_and_process_renames(struct merge_options *opt,
 				      struct string_list *entries,
 				      struct rename_info *ri)
 {
+	struct repository *r = the_repository;
 	struct diff_queue_struct *head_pairs, *merge_pairs;
 	struct hashmap *dir_re_head, *dir_re_merge;
 	int clean = 1;
@@ -2863,7 +2869,8 @@ static int detect_and_process_renames(struct merge_options *opt,
 	head_pairs = get_diffpairs(opt, common, head);
 	merge_pairs = get_diffpairs(opt, common, merge);
 
-	if (opt->detect_directory_renames) {
+	prepare_repo_settings(r);
+	if (r->settings->merge_directory_renames) {
 		dir_re_head = get_directory_renames(head_pairs);
 		dir_re_merge = get_directory_renames(merge_pairs);
 
@@ -3112,6 +3119,7 @@ static int handle_rename_normal(struct merge_options *opt,
 				const struct diff_filespec *b,
 				struct rename_conflict_info *ci)
 {
+	struct repository *r = the_repository;
 	struct rename *ren = ci->ren1;
 	struct merge_file_info mfi;
 	int clean;
@@ -3121,7 +3129,9 @@ static int handle_rename_normal(struct merge_options *opt,
 	clean = handle_content_merge(&mfi, opt, path, was_dirty(opt, path),
 				     o, a, b, ci);
 
-	if (clean && opt->detect_directory_renames == 1 &&
+	prepare_repo_settings(r);
+	if (clean &&
+	    r->settings->merge_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
 	    ren->dir_rename_original_dest) {
 		if (update_stages(opt, path,
 				  NULL,
@@ -3155,6 +3165,7 @@ static void dir_rename_warning(const char *msg,
 static int warn_about_dir_renamed_entries(struct merge_options *opt,
 					  struct rename *ren)
 {
+	struct repository *r = the_repository;
 	const char *msg;
 	int clean = 1, is_add;
 
@@ -3166,12 +3177,13 @@ static int warn_about_dir_renamed_entries(struct merge_options *opt,
 		return clean;
 
 	/* Sanity checks */
-	assert(opt->detect_directory_renames > 0);
+	prepare_repo_settings(r);
+	assert(r->settings->merge_directory_renames > 0);
 	assert(ren->dir_rename_original_type == 'A' ||
 	       ren->dir_rename_original_type == 'R');
 
 	/* Check whether to treat directory renames as a conflict */
-	clean = (opt->detect_directory_renames == 2);
+	clean = (r->settings->merge_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE);
 
 	is_add = (ren->dir_rename_original_type == 'A');
 	if (ren->dir_rename_original_type == 'A' && clean) {
@@ -3662,15 +3674,6 @@ static void merge_recursive_config(struct merge_options *opt)
 		opt->merge_detect_rename = git_config_rename("merge.renames", value);
 		free(value);
 	}
-	if (!git_config_get_string("merge.directoryrenames", &value)) {
-		int boolval = git_parse_maybe_bool(value);
-		if (0 <= boolval) {
-			opt->detect_directory_renames = boolval ? 2 : 0;
-		} else if (!strcasecmp(value, "conflict")) {
-			opt->detect_directory_renames = 1;
-		} /* avoid erroring on values from future versions of git */
-		free(value);
-	}
 	git_config(git_xmerge_config, NULL);
 }
 
@@ -3687,7 +3690,6 @@ void init_merge_options(struct merge_options *opt,
 	opt->renormalize = 0;
 	opt->diff_detect_rename = -1;
 	opt->merge_detect_rename = -1;
-	opt->detect_directory_renames = 1;
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/merge-recursive.h b/merge-recursive.h
index c2b7bb65c6..b8eba244ee 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -22,7 +22,6 @@ struct merge_options {
 	unsigned renormalize : 1;
 	long xdl_opts;
 	int verbosity;
-	int detect_directory_renames;
 	int diff_detect_rename;
 	int merge_detect_rename;
 	int diff_rename_limit;
diff --git a/repo-settings.c b/repo-settings.c
index 9e4b8e6268..5e9249c437 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -9,6 +9,12 @@ static int git_repo_config(const char *key, const char *value, void *cb)
 {
 	struct repo_settings *rs = (struct repo_settings *)cb;
 
+	if (!strcmp(key, "feature.experimental")) {
+		UPDATE_DEFAULT(rs->pack_use_sparse, 1);
+		UPDATE_DEFAULT(rs->merge_directory_renames, MERGE_DIRECTORY_RENAMES_TRUE);
+		UPDATE_DEFAULT(rs->fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
+		return 0;
+	}
 	if (!strcmp(key, "feature.manycommits")) {
 		UPDATE_DEFAULT(rs->core_commit_graph, 1);
 		UPDATE_DEFAULT(rs->gc_write_commit_graph, 1);
@@ -50,6 +56,23 @@ static int git_repo_config(const char *key, const char *value, void *cb)
 				"using 'keep' default value"), value);
 		return 0;
 	}
+	if (!strcmp(key, "merge.directoryrenames")) {
+		int bool_value = git_parse_maybe_bool(value);
+		if (0 <= bool_value) {
+			rs->merge_directory_renames = bool_value ? MERGE_DIRECTORY_RENAMES_TRUE : 0;
+		} else if (!strcasecmp(value, "conflict")) {
+			rs->merge_directory_renames = MERGE_DIRECTORY_RENAMES_CONFLICT;
+		}
+		return 0;
+	}
+	if (!strcmp(key, "fetch.negotiationalgorithm"))	{
+		if (!strcasecmp(value, "skipping")) {
+			rs->fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
+		} else {
+			rs->fetch_negotiation_algorithm = FETCH_NEGOTIATION_DEFAULT;
+		}
+		return 0;
+	}
 
 	return 1;
 }
@@ -64,10 +87,14 @@ void prepare_repo_settings(struct repository *r)
 	/* Defaults */
 	r->settings->core_commit_graph = -1;
 	r->settings->gc_write_commit_graph = -1;
-	r->settings->pack_use_sparse = -1;
+
 	r->settings->index_version = -1;
 	r->settings->core_untracked_cache = -1;
 
+	r->settings->pack_use_sparse = -1;
+	r->settings->merge_directory_renames = -1;
+	r->settings->fetch_negotiation_algorithm = -1;
+
 	repo_config(r, git_repo_config, r->settings);
 
 	/* Hack for test programs like test-dump-untracked-cache */
@@ -75,4 +102,7 @@ void prepare_repo_settings(struct repository *r)
 		r->settings->core_untracked_cache = CORE_UNTRACKED_CACHE_KEEP;
 	else
 		UPDATE_DEFAULT(r->settings->core_untracked_cache, CORE_UNTRACKED_CACHE_KEEP);
+
+	UPDATE_DEFAULT(r->settings->merge_directory_renames, MERGE_DIRECTORY_RENAMES_CONFLICT);
+	UPDATE_DEFAULT(r->settings->fetch_negotiation_algorithm, FETCH_NEGOTIATION_DEFAULT);
 }
diff --git a/repo-settings.h b/repo-settings.h
index bac9b87d49..cecf7d0028 100644
--- a/repo-settings.h
+++ b/repo-settings.h
@@ -4,12 +4,22 @@
 #define CORE_UNTRACKED_CACHE_WRITE (1 << 0)
 #define CORE_UNTRACKED_CACHE_KEEP (1 << 1)
 
+#define MERGE_DIRECTORY_RENAMES_CONFLICT 1
+#define MERGE_DIRECTORY_RENAMES_TRUE 2
+
+#define FETCH_NEGOTIATION_DEFAULT 1
+#define FETCH_NEGOTIATION_SKIPPING 2
+
 struct repo_settings {
 	int core_commit_graph;
 	int gc_write_commit_graph;
-	int pack_use_sparse;
+
 	int index_version;
 	int core_untracked_cache;
+
+	int pack_use_sparse;
+	int merge_directory_renames;
+	int fetch_negotiation_algorithm;
 };
 
 struct repository;
diff --git a/t/t5552-skipping-fetch-negotiator.sh b/t/t5552-skipping-fetch-negotiator.sh
index 8a14be51a1..f70cbcc9ca 100755
--- a/t/t5552-skipping-fetch-negotiator.sh
+++ b/t/t5552-skipping-fetch-negotiator.sh
@@ -60,29 +60,6 @@ test_expect_success 'commits with no parents are sent regardless of skip distanc
 	have_not_sent c6 c4 c3
 '
 
-test_expect_success 'unknown fetch.negotiationAlgorithm values error out' '
-	rm -rf server client trace &&
-	git init server &&
-	test_commit -C server to_fetch &&
-
-	git init client &&
-	test_commit -C client on_client &&
-	git -C client checkout on_client &&
-
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	test_must_fail git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep "unknown fetch negotiation algorithm" err &&
-
-	# Explicit "default" value
-	test_config -C client fetch.negotiationAlgorithm default &&
-	git -C client -c fetch.negotiationAlgorithm=default fetch "$(pwd)/server" &&
-
-	# Implementation detail: If there is nothing to fetch, we will not error out
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep ! "unknown fetch negotiation algorithm" err
-'
-
 test_expect_success 'when two skips collide, favor the larger one' '
 	rm -rf server client trace &&
 	git init server &&

Makefile, builtin/gc.c, builtin/pack-objects.c, commit-graph.c, read-cache.c, repo-settings.c, repo-settings.h, repository.h

diff --git a/Makefile b/Makefile
index 11ccea4071..032fe9b5f9 100644
--- a/Makefile
+++ b/Makefile
@@ -964,6 +964,7 @@ LIB_OBJS += refspec.o
 LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace-object.o
+LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
 LIB_OBJS += resolve-undo.o
diff --git a/builtin/gc.c b/builtin/gc.c
index c18efadda5..5e365049aa 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -27,6 +27,7 @@
 #include "pack-objects.h"
 #include "blob.h"
 #include "tree.h"
+#include "repo-settings.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -41,7 +42,6 @@ static int aggressive_depth = 50;
 static int aggressive_window = 250;
 static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
-static int gc_write_commit_graph;
 static int detach_auto = 1;
 static timestamp_t gc_log_expire_time;
 static const char *gc_log_expire = "1.day.ago";
@@ -148,7 +148,6 @@ static void gc_config(void)
 	git_config_get_int("gc.aggressivedepth", &aggressive_depth);
 	git_config_get_int("gc.auto", &gc_auto_threshold);
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
-	git_config_get_bool("gc.writecommitgraph", &gc_write_commit_graph);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_get_expiry("gc.pruneexpire", &prune_expire);
 	git_config_get_expiry("gc.worktreepruneexpire", &prune_worktrees_expire);
@@ -685,11 +684,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		clean_pack_garbage();
 	}
 
-	if (gc_write_commit_graph &&
-	    write_commit_graph_reachable(get_object_directory(),
-					 !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
-					 NULL))
-		return 1;
+	prepare_repo_settings(the_repository);
+	if (the_repository->settings.gc_write_commit_graph == 1)
+		write_commit_graph_reachable(get_object_directory(),
+					     !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
+					     NULL);
 
 	if (auto_gc && too_many_loose_objects())
 		warning(_("There are too many unreachable loose objects; "
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 267c562b1f..20bcd57033 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -34,6 +34,7 @@
 #include "dir.h"
 #include "midx.h"
 #include "trace2.h"
+#include "repo-settings.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -2709,10 +2710,6 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(k, "pack.usesparse")) {
-		sparse = git_config_bool(k, v);
-		return 0;
-	}
 	if (!strcmp(k, "pack.threads")) {
 		delta_search_threads = git_config_int(k, v);
 		if (delta_search_threads < 0)
@@ -3332,6 +3329,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	read_replace_refs = 0;
 
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
+	prepare_repo_settings(the_repository);
+	if (!sparse && the_repository->settings.pack_use_sparse != -1)
+		sparse = the_repository->settings.pack_use_sparse;
+
 	reset_pack_idx_option(&pack_idx_opts);
 	git_config(git_pack_config, NULL);
 
diff --git a/commit-graph.c b/commit-graph.c
index b3c4de79b6..0c2dadab9b 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -16,6 +16,7 @@
 #include "hashmap.h"
 #include "replace-object.h"
 #include "progress.h"
+#include "repo-settings.h"
 
 #define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
 #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
@@ -466,7 +467,6 @@ static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
 static int prepare_commit_graph(struct repository *r)
 {
 	struct object_directory *odb;
-	int config_value;
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
 		die("dying as requested by the '%s' variable on commit-graph load!",
@@ -476,9 +476,10 @@ static int prepare_commit_graph(struct repository *r)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
+	prepare_repo_settings(r);
+
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
-	    (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
-	    !config_value))
+	    r->settings.core_commit_graph != 1)
 		/*
 		 * This repository is not configured to use commit graphs, so
 		 * do not load one. (But report commit_graph_attempted anyway
diff --git a/read-cache.c b/read-cache.c
index c701f7f8b8..bda665a25a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -25,6 +25,7 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "repo-settings.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -1599,16 +1600,17 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
 
 #define INDEX_FORMAT_DEFAULT 3
 
-static unsigned int get_index_format_default(void)
+static unsigned int get_index_format_default(struct repository *r)
 {
 	char *envversion = getenv("GIT_INDEX_VERSION");
 	char *endp;
-	int value;
 	unsigned int version = INDEX_FORMAT_DEFAULT;
 
 	if (!envversion) {
-		if (!git_config_get_int("index.version", &value))
-			version = value;
+		prepare_repo_settings(r);
+
+		if (r->settings.index_version >= 0)
+			version = r->settings.index_version;
 		if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
 			warning(_("index.version set, but the value is invalid.\n"
 				  "Using version %i"), INDEX_FORMAT_DEFAULT);
@@ -2765,7 +2767,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	}
 
 	if (!istate->version) {
-		istate->version = get_index_format_default();
+		istate->version = get_index_format_default(the_repository);
 		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}
diff --git a/repo-settings.c b/repo-settings.c
new file mode 100644
index 0000000000..2c33810cc6
--- /dev/null
+++ b/repo-settings.c
@@ -0,0 +1,28 @@
+#include "cache.h"
+#include "repository.h"
+#include "config.h"
+#include "repo-settings.h"
+
+void prepare_repo_settings(struct repository *r)
+{
+	int value;
+
+	if (r->settings_initialized)
+		return;
+
+	/* Defaults */
+	memset(&r->settings, -1, sizeof(r->settings));
+
+	if (!repo_config_get_bool(r, "core.commitgraph", &value))
+		r->settings.core_commit_graph = value;
+	if (!repo_config_get_bool(r, "gc.writecommitgraph", &value))
+		r->settings.gc_write_commit_graph = value;
+
+	if (!repo_config_get_bool(r, "index.version", &value))
+		r->settings.index_version = value;
+
+	if (!repo_config_get_bool(r, "pack.usesparse", &value))
+		r->settings.pack_use_sparse = value;
+
+	r->settings_initialized = 1;
+}
diff --git a/repo-settings.h b/repo-settings.h
new file mode 100644
index 0000000000..89fb0159bf
--- /dev/null
+++ b/repo-settings.h
@@ -0,0 +1,17 @@
+#ifndef REPO_SETTINGS_H
+#define REPO_SETTINGS_H
+
+struct repo_settings {
+	int core_commit_graph;
+	int gc_write_commit_graph;
+
+	int index_version;
+
+	int pack_use_sparse;
+};
+
+struct repository;
+
+void prepare_repo_settings(struct repository *r);
+
+#endif /* REPO_SETTINGS_H */
diff --git a/repository.h b/repository.h
index 4fb6a5885f..a817486825 100644
--- a/repository.h
+++ b/repository.h
@@ -2,8 +2,10 @@
 #define REPOSITORY_H
 
 #include "path.h"
+#include "repo-settings.h"
 
 struct config_set;
+struct repo_settings;
 struct git_hash_algo;
 struct index_state;
 struct lock_file;
@@ -72,6 +74,9 @@ struct repository {
 	 */
 	char *submodule_prefix;
 
+	int settings_initialized;
+	struct repo_settings settings;
+
 	/* Subsystems */
 	/*
 	 * Repository's config which contains key-value pairs from the usual

Documentation/config.txt, Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/gc.txt, repo-settings.c

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e3f5bc3396..77f3b1486b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -345,6 +345,8 @@ include::config/difftool.txt[]
 
 include::config/fastimport.txt[]
 
+include::config/feature.txt[]
+
 include::config/fetch.txt[]
 
 include::config/format.txt[]
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 75538d27e7..d80162681a 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -577,7 +577,8 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to false, unless
+	`feature.manyCommits` is enabled. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
new file mode 100644
index 0000000000..f74314ae90
--- /dev/null
+++ b/Documentation/config/feature.txt
@@ -0,0 +1,15 @@
+feature.*::
+	The config settings that start with `feature.` modify the defaults of
+	a group of other config settings. These groups are created by the Git
+	developer community as recommended defaults and are subject to change.
+	In particular, new config options may be added with different defaults.
+
+feature.manyCommits::
+	Enable config options that optimize for repos with many commits. This
+	setting is recommended for repos with at least 100,000 commits. The
+	new default values are:
++
+* `core.commitGraph=true` enables reading the commit-graph file.
++
+* `gc.writeCommitGraph=true` enables writing the commit-graph file during
+garbage collection.
\ No newline at end of file
diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 02b92b18b5..31a5fc4f75 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -63,8 +63,8 @@ gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
 	linkgit:git-gc[1] is run. When using `git gc --auto`
 	the commit-graph will be updated if housekeeping is
-	required. Default is false. See linkgit:git-commit-graph[1]
-	for details.
+	required. Default is false, unless `feature.manyCommits`
+	is enabled. See linkgit:git-commit-graph[1] for details.
 
 gc.logExpiry::
 	If the file gc.log exists, then `git gc --auto` will print
diff --git a/repo-settings.c b/repo-settings.c
index 2c33810cc6..3face7d8b9 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -3,6 +3,8 @@
 #include "config.h"
 #include "repo-settings.h"
 
+#define UPDATE_DEFAULT(s,v) do { if (s == -1) { s = v; } } while(0)
+
 void prepare_repo_settings(struct repository *r)
 {
 	int value;
@@ -24,5 +26,10 @@ void prepare_repo_settings(struct repository *r)
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
 
+	if (!repo_config_get_bool(r, "feature.manycommits", &value) && value) {
+		UPDATE_DEFAULT(r->settings.core_commit_graph, 1);
+		UPDATE_DEFAULT(r->settings.gc_write_commit_graph, 1);
+	}
+
 	r->settings_initialized = 1;
 }

builtin/update-index.c, config.c, read-cache.c, repo-settings.c, repo-settings.h

diff --git a/builtin/update-index.c b/builtin/update-index.c
index dff2f4b837..5ced51c1ee 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -18,6 +18,7 @@
 #include "dir.h"
 #include "split-index.h"
 #include "fsmonitor.h"
+#include "repo-settings.h"
 
 /*
  * Default to not allowing changes to the list of files. The
@@ -966,6 +967,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	struct parse_opt_ctx_t ctx;
 	strbuf_getline_fn getline_fn;
 	int parseopt_state = PARSE_OPT_UNKNOWN;
+	struct repository *r = the_repository;
 	struct option options[] = {
 		OPT_BIT('q', NULL, &refresh_args.flags,
 			N_("continue refresh even when index needs update"),
@@ -1180,11 +1182,12 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		remove_split_index(&the_index);
 	}
 
+	prepare_repo_settings(r);
 	switch (untracked_cache) {
 	case UC_UNSPECIFIED:
 		break;
 	case UC_DISABLE:
-		if (git_config_get_untracked_cache() == 1)
+		if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
 			warning(_("core.untrackedCache is set to true; "
 				  "remove or change it, if you really want to "
 				  "disable the untracked cache"));
@@ -1196,7 +1199,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		return !test_if_untracked_cache_is_supported();
 	case UC_ENABLE:
 	case UC_FORCE:
-		if (git_config_get_untracked_cache() == 0)
+		if (r->settings.core_untracked_cache == UNTRACKED_CACHE_REMOVE)
 			warning(_("core.untrackedCache is set to false; "
 				  "remove or change it, if you really want to "
 				  "enable the untracked cache"));
diff --git a/config.c b/config.c
index faa57e436c..3241dbc54d 100644
--- a/config.c
+++ b/config.c
@@ -2277,30 +2277,6 @@ int git_config_get_expiry_in_days(const char *key, timestamp_t *expiry, timestam
 	return -1; /* thing exists but cannot be parsed */
 }
 
-int git_config_get_untracked_cache(void)
-{
-	int val = -1;
-	const char *v;
-
-	/* Hack for test programs like test-dump-untracked-cache */
-	if (ignore_untracked_cache_config)
-		return -1;
-
-	if (!git_config_get_maybe_bool("core.untrackedcache", &val))
-		return val;
-
-	if (!git_config_get_value("core.untrackedcache", &v)) {
-		if (!strcasecmp(v, "keep"))
-			return -1;
-
-		error(_("unknown core.untrackedCache value '%s'; "
-			"using 'keep' default value"), v);
-		return -1;
-	}
-
-	return -1; /* default value */
-}
-
 int git_config_get_split_index(void)
 {
 	int val;
diff --git a/read-cache.c b/read-cache.c
index bda665a25a..3761b9a171 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1846,18 +1846,17 @@ static void check_ce_order(struct index_state *istate)
 
 static void tweak_untracked_cache(struct index_state *istate)
 {
-	switch (git_config_get_untracked_cache()) {
-	case -1: /* keep: do nothing */
-		break;
-	case 0: /* false */
+	struct repository *r = the_repository;
+
+	prepare_repo_settings(r);
+
+	if (r->settings.core_untracked_cache  == UNTRACKED_CACHE_REMOVE) {
 		remove_untracked_cache(istate);
-		break;
-	case 1: /* true */
-		add_untracked_cache(istate);
-		break;
-	default: /* unknown value: do nothing */
-		break;
+		return;
 	}
+
+	if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
+		add_untracked_cache(istate);
 }
 
 static void tweak_split_index(struct index_state *istate)
diff --git a/repo-settings.c b/repo-settings.c
index 3face7d8b9..65b980403c 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -8,6 +8,7 @@
 void prepare_repo_settings(struct repository *r)
 {
 	int value;
+	char *strval;
 
 	if (r->settings_initialized)
 		return;
@@ -22,14 +23,32 @@ void prepare_repo_settings(struct repository *r)
 
 	if (!repo_config_get_bool(r, "index.version", &value))
 		r->settings.index_version = value;
+	if (!repo_config_get_maybe_bool(r, "core.untrackedcache", &value)) {
+		if (value == 0)
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_REMOVE;
+		else
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_WRITE;
+	} else if (!repo_config_get_string(r, "core.untrackedcache", &strval)) {
+		if (!strcasecmp(strval, "keep"))
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
+
+		free(strval);
+	}
+
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
-
+	
 	if (!repo_config_get_bool(r, "feature.manycommits", &value) && value) {
 		UPDATE_DEFAULT(r->settings.core_commit_graph, 1);
 		UPDATE_DEFAULT(r->settings.gc_write_commit_graph, 1);
 	}
 
+	/* Hack for test programs like test-dump-untracked-cache */
+	if (ignore_untracked_cache_config)
+		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
+	else
+		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
+
 	r->settings_initialized = 1;
 }
diff --git a/repo-settings.h b/repo-settings.h
index 89fb0159bf..e9b028e1a9 100644
--- a/repo-settings.h
+++ b/repo-settings.h
@@ -1,11 +1,19 @@
 #ifndef REPO_SETTINGS_H
 #define REPO_SETTINGS_H
 
+enum untracked_cache_setting {
+	UNTRACKED_CACHE_UNSET = -1,
+	UNTRACKED_CACHE_REMOVE = 0,
+	UNTRACKED_CACHE_KEEP = 1,
+	UNTRACKED_CACHE_WRITE = 2
+};
+
 struct repo_settings {
 	int core_commit_graph;
 	int gc_write_commit_graph;
 
 	int index_version;
+	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
 };

Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/index.txt, repo-settings.c, t/t1600-index.sh

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index d80162681a..7a2a33bc8c 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -86,7 +86,9 @@ core.untrackedCache::
 	it will automatically be removed, if set to `false`. Before
 	setting it to `true`, you should check that mtime is working
 	properly on your system.
-	See linkgit:git-update-index[1]. `keep` by default.
+	See linkgit:git-update-index[1]. `keep` by default, unless
+	`feature.manyFiles` is enabled which sets this setting to
+	`true` by default.
 
 core.checkStat::
 	When missing or is set to `default`, many fields in the stat
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index f74314ae90..c2d9ef7473 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -12,4 +12,14 @@ feature.manyCommits::
 * `core.commitGraph=true` enables reading the commit-graph file.
 +
 * `gc.writeCommitGraph=true` enables writing the commit-graph file during
-garbage collection.
\ No newline at end of file
+garbage collection.
+
+feature.manyFiles::
+	Enable config options that optimize for repos with many files in the
+	working directory. With many files, commands such as `git status` and
+	`git checkout` may be slow and these new defaults improve performance:
++
+* `index.version=4` enables path-prefix compression in the index.
++
+* `core.untrackedCache=true` enables the untracked cache. This setting assumes
+that mtime is working on your machine.
\ No newline at end of file
diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
index f181503041..7cb50b37e9 100644
--- a/Documentation/config/index.txt
+++ b/Documentation/config/index.txt
@@ -24,3 +24,4 @@ index.threads::
 index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.
+	If `feature.manyFiles` is enabled, then the default is 4.
diff --git a/repo-settings.c b/repo-settings.c
index 65b980403c..3a5cf33814 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -43,6 +43,10 @@ void prepare_repo_settings(struct repository *r)
 		UPDATE_DEFAULT(r->settings.core_commit_graph, 1);
 		UPDATE_DEFAULT(r->settings.gc_write_commit_graph, 1);
 	}
+	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
+		UPDATE_DEFAULT(r->settings.index_version, 4);
+		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
+	}
 
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
diff --git a/t/t1600-index.sh b/t/t1600-index.sh
index 42962ed7d4..c77721b580 100755
--- a/t/t1600-index.sh
+++ b/t/t1600-index.sh
@@ -59,17 +59,38 @@ test_expect_success 'out of bounds index.version issues warning' '
 	)
 '
 
-test_expect_success 'GIT_INDEX_VERSION takes precedence over config' '
+test_index_version () {
+	INDEX_VERSION_CONFIG=$1 &&
+	FEATURE_MANY_FILES=$2 &&
+	ENV_VAR_VERSION=$3
+	EXPECTED_OUTPUT_VERSION=$4 &&
 	(
 		rm -f .git/index &&
-		GIT_INDEX_VERSION=4 &&
-		export GIT_INDEX_VERSION &&
-		git config --add index.version 2 &&
+		rm -f .git/config &&
+		if test "$INDEX_VERSION_CONFIG" -ne 0
+		then
+			git config --add index.version $INDEX_VERSION_CONFIG
+		fi &&
+		git config --add feature.manyFiles $FEATURE_MANY_FILES
+		if test "$ENV_VAR_VERSION" -ne 0
+		then
+			GIT_INDEX_VERSION=$ENV_VAR_VERSION &&
+			export GIT_INDEX_VERSION
+		else
+			unset GIT_INDEX_VERSION
+		fi &&
 		git add a 2>&1 &&
-		echo 4 >expect &&
+		echo $EXPECTED_OUTPUT_VERSION >expect &&
 		test-tool index-version <.git/index >actual &&
 		test_cmp expect actual
 	)
+}
+
+test_expect_success 'index version config precedence' '
+	test_index_version 2 false 4 4 &&
+	test_index_version 2 true 0 2 &&
+	test_index_version 0 true 0 4 &&
+	test_index_version 0 true 2 2
 '
 
 test_done

Documentation/config/feature.txt, Documentation/config/fetch.txt, Documentation/config/merge.txt, Documentation/config/pack.txt, builtin/am.c, fetch-negotiator.c, fetch-negotiator.h, fetch-pack.c, merge-recursive.c, repo-settings.c, repo-settings.h, t/t5552-skipping-fetch-negotiator.sh

diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index c2d9ef7473..287621b1e8 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -4,6 +4,23 @@ feature.*::
 	developer community as recommended defaults and are subject to change.
 	In particular, new config options may be added with different defaults.
 
+feature.experimental::
+	Enable config options that are new to Git, and are being considered for
+	future defaults. Config settings included here may be added or removed
+	with each release, including minor version updates. These settings may
+	have unintended interactions since they are so new. Please enable this
+	setting if you are interested in providing feedback on experimental
+	features. The new default values are:
++
+* `pack.useSparse=true` uses a new algorithm when constructing a pack-file
+which can improve `git push` performance in repos with many files.
++
+* `merge.directoryRenames=true` uses a new algorithm for detecting renames by
+using entire directories at a time instead of single files at a time.
++
+* `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
+skipping more commits at a time, reducing the number of round trips.
+
 feature.manyCommits::
 	Enable config options that optimize for repos with many commits. This
 	setting is recommended for repos with at least 100,000 commits. The
diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
index ba890b5884..d402110638 100644
--- a/Documentation/config/fetch.txt
+++ b/Documentation/config/fetch.txt
@@ -59,7 +59,8 @@ fetch.negotiationAlgorithm::
 	effort to converge faster, but may result in a larger-than-necessary
 	packfile; The default is "default" which instructs Git to use the default algorithm
 	that never skips commits (unless the server has acknowledged it or one
-	of its descendants).
+	of its descendants). If `feature.experimental` is enabled, then this
+	setting defaults to "skipping".
 	Unknown values will cause 'git fetch' to error out.
 +
 See also the `--negotiation-tip` option for linkgit:git-fetch[1].
diff --git a/Documentation/config/merge.txt b/Documentation/config/merge.txt
index 6a313937f8..e8def2d63c 100644
--- a/Documentation/config/merge.txt
+++ b/Documentation/config/merge.txt
@@ -54,7 +54,8 @@ merge.directoryRenames::
 	moved into the new directory.  If set to "conflict", a conflict
 	will be reported for such paths.  If merge.renames is false,
 	merge.directoryRenames is ignored and treated as false.  Defaults
-	to "conflict".
+	to "conflict" unless `feature.experimental` is enabled and the
+	default is "true".
 
 merge.renormalize::
 	Tell Git that canonical representation of files in the
diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index 9cdcfa7324..1d66f0c992 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -112,7 +112,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames.
+	commits contain certain types of direct renames. Default is `false`
+	unless `feature.experimental` is enabled.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.
diff --git a/builtin/am.c b/builtin/am.c
index 1aea657a7f..912c6155b8 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -34,6 +34,7 @@
 #include "string-list.h"
 #include "packfile.h"
 #include "repository.h"
+#include "repo-settings.h"
 
 /**
  * Returns the length of the first line of msg.
diff --git a/fetch-negotiator.c b/fetch-negotiator.c
index d6d685cba0..1a68be1a2e 100644
--- a/fetch-negotiator.c
+++ b/fetch-negotiator.c
@@ -2,19 +2,21 @@
 #include "fetch-negotiator.h"
 #include "negotiator/default.h"
 #include "negotiator/skipping.h"
+#include "repository.h"
+#include "repo-settings.h"
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm)
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator)
 {
-	if (algorithm) {
-		if (!strcmp(algorithm, "skipping")) {
-			skipping_negotiator_init(negotiator);
-			return;
-		} else if (!strcmp(algorithm, "default")) {
-			/* Fall through to default initialization */
-		} else {
-			die("unknown fetch negotiation algorithm '%s'", algorithm);
-		}
+	prepare_repo_settings(r);
+	switch(r->settings.fetch_negotiation_algorithm) {
+	case FETCH_NEGOTIATION_SKIPPING:
+		skipping_negotiator_init(negotiator);
+		return;
+
+	case FETCH_NEGOTIATION_DEFAULT:
+	default:
+		default_negotiator_init(negotiator);
+		return;
 	}
-	default_negotiator_init(negotiator);
 }
diff --git a/fetch-negotiator.h b/fetch-negotiator.h
index 9e3967ce66..ea78868504 100644
--- a/fetch-negotiator.h
+++ b/fetch-negotiator.h
@@ -2,6 +2,7 @@
 #define FETCH_NEGOTIATOR_H
 
 struct commit;
+struct repository;
 
 /*
  * An object that supplies the information needed to negotiate the contents of
@@ -52,7 +53,7 @@ struct fetch_negotiator {
 	void *data;
 };
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm);
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator);
 
 #endif
diff --git a/fetch-pack.c b/fetch-pack.c
index 65be043f2a..d81f47c07b 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -36,7 +36,6 @@ static int agent_supported;
 static int server_supports_filtering;
 static struct lock_file shallow_lock;
 static const char *alternate_shallow_file;
-static char *negotiation_algorithm;
 static struct strbuf fsck_msg_types = STRBUF_INIT;
 
 /* Remember to update object flag allocation in object.h */
@@ -892,12 +891,13 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 				 struct shallow_info *si,
 				 char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	struct object_id oid;
 	const char *agent_feature;
 	int agent_len;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 
 	sort_ref_list(&ref, ref_compare_name);
 	QSORT(sought, nr_sought, cmp_ref_by_name);
@@ -911,7 +911,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 
 	if (server_supports("shallow"))
 		print_verbose(args, _("Server supports %s"), "shallow");
-	else if (args->depth > 0 || is_repository_shallow(the_repository))
+	else if (args->depth > 0 || is_repository_shallow(r))
 		die(_("Server does not support shallow clients"));
 	if (args->depth > 0 || args->deepen_since || args->deepen_not)
 		args->deepen = 1;
@@ -1379,6 +1379,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				    struct shallow_info *si,
 				    char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	enum fetch_state state = FETCH_CHECK_LOCAL;
 	struct oidset common = OIDSET_INIT;
@@ -1386,7 +1387,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	int in_vain = 0;
 	int haves_to_send = INITIAL_FLUSH;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 	packet_reader_init(&reader, fd[0], NULL, 0,
 			   PACKET_READ_CHOMP_NEWLINE |
 			   PACKET_READ_DIE_ON_ERR_PACKET);
@@ -1505,8 +1506,6 @@ static void fetch_pack_config(void)
 	git_config_get_bool("repack.usedeltabaseoffset", &prefer_ofs_delta);
 	git_config_get_bool("fetch.fsckobjects", &fetch_fsck_objects);
 	git_config_get_bool("transfer.fsckobjects", &transfer_fsck_objects);
-	git_config_get_string("fetch.negotiationalgorithm",
-			      &negotiation_algorithm);
 
 	git_config(fetch_pack_config_cb, NULL);
 }
diff --git a/merge-recursive.c b/merge-recursive.c
index 12300131fc..f39c31c9c4 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -28,6 +28,7 @@
 #include "submodule.h"
 #include "revision.h"
 #include "commit-reach.h"
+#include "repo-settings.h"
 
 struct path_hashmap_entry {
 	struct hashmap_entry e;
@@ -3662,15 +3663,6 @@ static void merge_recursive_config(struct merge_options *opt)
 		opt->merge_detect_rename = git_config_rename("merge.renames", value);
 		free(value);
 	}
-	if (!git_config_get_string("merge.directoryrenames", &value)) {
-		int boolval = git_parse_maybe_bool(value);
-		if (0 <= boolval) {
-			opt->detect_directory_renames = boolval ? 2 : 0;
-		} else if (!strcasecmp(value, "conflict")) {
-			opt->detect_directory_renames = 1;
-		} /* avoid erroring on values from future versions of git */
-		free(value);
-	}
 	git_config(git_xmerge_config, NULL);
 }
 
@@ -3688,6 +3680,11 @@ void init_merge_options(struct merge_options *opt,
 	opt->diff_detect_rename = -1;
 	opt->merge_detect_rename = -1;
 	opt->detect_directory_renames = 1;
+
+	prepare_repo_settings(repo);
+	if (repo->settings.merge_directory_renames >= 0)
+		opt->detect_directory_renames = repo->settings.merge_directory_renames;
+
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/repo-settings.c b/repo-settings.c
index 3a5cf33814..bfb3288fda 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -35,6 +35,18 @@ void prepare_repo_settings(struct repository *r)
 		free(strval);
 	}
 
+	if (!repo_config_get_maybe_bool(r, "merge.directoryrenames", &value))
+		r->settings.merge_directory_renames = value ? MERGE_DIRECTORY_RENAMES_TRUE : 0;
+	else if (!repo_config_get_string(r, "merge.directoryrenames", &strval)) {
+		if (!strcasecmp(strval, "conflict"))
+			r->settings.merge_directory_renames = MERGE_DIRECTORY_RENAMES_CONFLICT;
+	}
+	if (!repo_config_get_string(r, "fetch.negotiationalgorithm", &strval)) {
+		if (!strcasecmp(strval, "skipping"))
+			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
+		else
+			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_DEFAULT;
+	}
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
@@ -47,6 +59,11 @@ void prepare_repo_settings(struct repository *r)
 		UPDATE_DEFAULT(r->settings.index_version, 4);
 		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
 	}
+	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
+		UPDATE_DEFAULT(r->settings.pack_use_sparse, 1);
+		UPDATE_DEFAULT(r->settings.merge_directory_renames, MERGE_DIRECTORY_RENAMES_TRUE);
+		UPDATE_DEFAULT(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
+	}
 
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
@@ -54,5 +71,8 @@ void prepare_repo_settings(struct repository *r)
 	else
 		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
 
+	UPDATE_DEFAULT(r->settings.merge_directory_renames, MERGE_DIRECTORY_RENAMES_CONFLICT);
+	UPDATE_DEFAULT(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_DEFAULT);
+
 	r->settings_initialized = 1;
 }
diff --git a/repo-settings.h b/repo-settings.h
index e9b028e1a9..95d3392df2 100644
--- a/repo-settings.h
+++ b/repo-settings.h
@@ -8,6 +8,20 @@ enum untracked_cache_setting {
 	UNTRACKED_CACHE_WRITE = 2
 };
 
+enum merge_directory_renames_setting {
+	MERGE_DIRECTORY_RENAMES_UNSET = -1,
+	MERGE_DIRECTORY_RENAMES_NONE = 0,
+	MERGE_DIRECTORY_RENAMES_CONFLICT = 1,
+	MERGE_DIRECTORY_RENAMES_TRUE = 2,
+};
+
+enum fetch_negotiation_setting {
+	FETCH_NEGOTIATION_UNSET = -1,
+	FETCH_NEGOTIATION_NONE = 0,
+	FETCH_NEGOTIATION_DEFAULT = 1,
+	FETCH_NEGOTIATION_SKIPPING = 2,
+};
+
 struct repo_settings {
 	int core_commit_graph;
 	int gc_write_commit_graph;
@@ -16,6 +30,8 @@ struct repo_settings {
 	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
+	enum merge_directory_renames_setting merge_directory_renames;
+	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 };
 
 struct repository;
diff --git a/t/t5552-skipping-fetch-negotiator.sh b/t/t5552-skipping-fetch-negotiator.sh
index 8a14be51a1..f70cbcc9ca 100755
--- a/t/t5552-skipping-fetch-negotiator.sh
+++ b/t/t5552-skipping-fetch-negotiator.sh
@@ -60,29 +60,6 @@ test_expect_success 'commits with no parents are sent regardless of skip distanc
 	have_not_sent c6 c4 c3
 '
 
-test_expect_success 'unknown fetch.negotiationAlgorithm values error out' '
-	rm -rf server client trace &&
-	git init server &&
-	test_commit -C server to_fetch &&
-
-	git init client &&
-	test_commit -C client on_client &&
-	git -C client checkout on_client &&
-
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	test_must_fail git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep "unknown fetch negotiation algorithm" err &&
-
-	# Explicit "default" value
-	test_config -C client fetch.negotiationAlgorithm default &&
-	git -C client -c fetch.negotiationAlgorithm=default fetch "$(pwd)/server" &&
-
-	# Implementation detail: If there is nothing to fetch, we will not error out
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep ! "unknown fetch negotiation algorithm" err
-'
-
 test_expect_success 'when two skips collide, favor the larger one' '
 	rm -rf server client trace &&
 	git init server &&

Documentation/config.txt, Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/gc.txt, repo-settings.c

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e3f5bc3396..77f3b1486b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -345,6 +345,8 @@ include::config/difftool.txt[]
 
 include::config/fastimport.txt[]
 
+include::config/feature.txt[]
+
 include::config/fetch.txt[]
 
 include::config/format.txt[]
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 75538d27e7..d80162681a 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -577,7 +577,8 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to false, unless
+	`feature.manyCommits` is enabled. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
new file mode 100644
index 0000000000..f74314ae90
--- /dev/null
+++ b/Documentation/config/feature.txt
@@ -0,0 +1,15 @@
+feature.*::
+	The config settings that start with `feature.` modify the defaults of
+	a group of other config settings. These groups are created by the Git
+	developer community as recommended defaults and are subject to change.
+	In particular, new config options may be added with different defaults.
+
+feature.manyCommits::
+	Enable config options that optimize for repos with many commits. This
+	setting is recommended for repos with at least 100,000 commits. The
+	new default values are:
++
+* `core.commitGraph=true` enables reading the commit-graph file.
++
+* `gc.writeCommitGraph=true` enables writing the commit-graph file during
+garbage collection.
\ No newline at end of file
diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 02b92b18b5..31a5fc4f75 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -63,8 +63,8 @@ gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
 	linkgit:git-gc[1] is run. When using `git gc --auto`
 	the commit-graph will be updated if housekeeping is
-	required. Default is false. See linkgit:git-commit-graph[1]
-	for details.
+	required. Default is false, unless `feature.manyCommits`
+	is enabled. See linkgit:git-commit-graph[1] for details.
 
 gc.logExpiry::
 	If the file gc.log exists, then `git gc --auto` will print
diff --git a/repo-settings.c b/repo-settings.c
index 309577f6bc..fc05f4fbc4 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -2,6 +2,8 @@
 #include "config.h"
 #include "repository.h"
 
+#define UPDATE_DEFAULT(s,v) do { if (s == -1) { s = v; } } while(0)
+
 void prepare_repo_settings(struct repository *r)
 {
 	int value;
@@ -22,4 +24,9 @@ void prepare_repo_settings(struct repository *r)
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
+
+	if (!repo_config_get_bool(r, "feature.manycommits", &value) && value) {
+		UPDATE_DEFAULT(r->settings.core_commit_graph, 1);
+		UPDATE_DEFAULT(r->settings.gc_write_commit_graph, 1);
+	}
 }

Makefile, builtin/gc.c, builtin/pack-objects.c, commit-graph.c, read-cache.c, repo-settings.c, repository.h

diff --git a/Makefile b/Makefile
index 11ccea4071..032fe9b5f9 100644
--- a/Makefile
+++ b/Makefile
@@ -964,6 +964,7 @@ LIB_OBJS += refspec.o
 LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace-object.o
+LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
 LIB_OBJS += resolve-undo.o
diff --git a/builtin/gc.c b/builtin/gc.c
index c18efadda5..4b8fbb9965 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -41,7 +41,6 @@ static int aggressive_depth = 50;
 static int aggressive_window = 250;
 static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
-static int gc_write_commit_graph;
 static int detach_auto = 1;
 static timestamp_t gc_log_expire_time;
 static const char *gc_log_expire = "1.day.ago";
@@ -148,7 +147,6 @@ static void gc_config(void)
 	git_config_get_int("gc.aggressivedepth", &aggressive_depth);
 	git_config_get_int("gc.auto", &gc_auto_threshold);
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
-	git_config_get_bool("gc.writecommitgraph", &gc_write_commit_graph);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_get_expiry("gc.pruneexpire", &prune_expire);
 	git_config_get_expiry("gc.worktreepruneexpire", &prune_worktrees_expire);
@@ -685,11 +683,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		clean_pack_garbage();
 	}
 
-	if (gc_write_commit_graph &&
-	    write_commit_graph_reachable(get_object_directory(),
-					 !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
-					 NULL))
-		return 1;
+	prepare_repo_settings(the_repository);
+	if (the_repository->settings.gc_write_commit_graph == 1)
+		write_commit_graph_reachable(get_object_directory(),
+					     !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
+					     NULL);
 
 	if (auto_gc && too_many_loose_objects())
 		warning(_("There are too many unreachable loose objects; "
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 267c562b1f..f9f7181f3f 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2709,10 +2709,6 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(k, "pack.usesparse")) {
-		sparse = git_config_bool(k, v);
-		return 0;
-	}
 	if (!strcmp(k, "pack.threads")) {
 		delta_search_threads = git_config_int(k, v);
 		if (delta_search_threads < 0)
@@ -3332,6 +3328,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	read_replace_refs = 0;
 
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
+	prepare_repo_settings(the_repository);
+	if (!sparse && the_repository->settings.pack_use_sparse != -1)
+		sparse = the_repository->settings.pack_use_sparse;
+
 	reset_pack_idx_option(&pack_idx_opts);
 	git_config(git_pack_config, NULL);
 
diff --git a/commit-graph.c b/commit-graph.c
index b3c4de79b6..7854e491b2 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -466,7 +466,6 @@ static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
 static int prepare_commit_graph(struct repository *r)
 {
 	struct object_directory *odb;
-	int config_value;
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
 		die("dying as requested by the '%s' variable on commit-graph load!",
@@ -476,9 +475,10 @@ static int prepare_commit_graph(struct repository *r)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
+	prepare_repo_settings(r);
+
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
-	    (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
-	    !config_value))
+	    r->settings.core_commit_graph != 1)
 		/*
 		 * This repository is not configured to use commit graphs, so
 		 * do not load one. (But report commit_graph_attempted anyway
diff --git a/read-cache.c b/read-cache.c
index c701f7f8b8..59dbebc15d 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1599,16 +1599,17 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
 
 #define INDEX_FORMAT_DEFAULT 3
 
-static unsigned int get_index_format_default(void)
+static unsigned int get_index_format_default(struct repository *r)
 {
 	char *envversion = getenv("GIT_INDEX_VERSION");
 	char *endp;
-	int value;
 	unsigned int version = INDEX_FORMAT_DEFAULT;
 
 	if (!envversion) {
-		if (!git_config_get_int("index.version", &value))
-			version = value;
+		prepare_repo_settings(r);
+
+		if (r->settings.index_version >= 0)
+			version = r->settings.index_version;
 		if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
 			warning(_("index.version set, but the value is invalid.\n"
 				  "Using version %i"), INDEX_FORMAT_DEFAULT);
@@ -2765,7 +2766,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	}
 
 	if (!istate->version) {
-		istate->version = get_index_format_default();
+		istate->version = get_index_format_default(the_repository);
 		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}
diff --git a/repo-settings.c b/repo-settings.c
new file mode 100644
index 0000000000..309577f6bc
--- /dev/null
+++ b/repo-settings.c
@@ -0,0 +1,25 @@
+#include "cache.h"
+#include "config.h"
+#include "repository.h"
+
+void prepare_repo_settings(struct repository *r)
+{
+	int value;
+
+	if (r->settings.initialized)
+		return;
+
+	/* Defaults */
+	memset(&r->settings, -1, sizeof(r->settings));
+
+	if (!repo_config_get_bool(r, "core.commitgraph", &value))
+		r->settings.core_commit_graph = value;
+	if (!repo_config_get_bool(r, "gc.writecommitgraph", &value))
+		r->settings.gc_write_commit_graph = value;
+
+	if (!repo_config_get_bool(r, "index.version", &value))
+		r->settings.index_version = value;
+
+	if (!repo_config_get_bool(r, "pack.usesparse", &value))
+		r->settings.pack_use_sparse = value;
+}
diff --git a/repository.h b/repository.h
index 4fb6a5885f..2bb2bc3eea 100644
--- a/repository.h
+++ b/repository.h
@@ -4,6 +4,7 @@
 #include "path.h"
 
 struct config_set;
+struct repo_settings;
 struct git_hash_algo;
 struct index_state;
 struct lock_file;
@@ -11,6 +12,17 @@ struct pathspec;
 struct raw_object_store;
 struct submodule_cache;
 
+struct repo_settings {
+	int initialized;
+
+	int core_commit_graph;
+	int gc_write_commit_graph;
+
+	int index_version;
+
+	int pack_use_sparse;
+};
+
 struct repository {
 	/* Environment */
 	/*
@@ -72,6 +84,8 @@ struct repository {
 	 */
 	char *submodule_prefix;
 
+	struct repo_settings settings;
+
 	/* Subsystems */
 	/*
 	 * Repository's config which contains key-value pairs from the usual
@@ -157,5 +171,6 @@ int repo_read_index_unmerged(struct repository *);
  */
 void repo_update_index_if_able(struct repository *, struct lock_file *);
 
+void prepare_repo_settings(struct repository *r);
 
 #endif /* REPOSITORY_H */

Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/index.txt, repo-settings.c, t/t1600-index.sh

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index d80162681a..7a2a33bc8c 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -86,7 +86,9 @@ core.untrackedCache::
 	it will automatically be removed, if set to `false`. Before
 	setting it to `true`, you should check that mtime is working
 	properly on your system.
-	See linkgit:git-update-index[1]. `keep` by default.
+	See linkgit:git-update-index[1]. `keep` by default, unless
+	`feature.manyFiles` is enabled which sets this setting to
+	`true` by default.
 
 core.checkStat::
 	When missing or is set to `default`, many fields in the stat
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index f74314ae90..c2d9ef7473 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -12,4 +12,14 @@ feature.manyCommits::
 * `core.commitGraph=true` enables reading the commit-graph file.
 +
 * `gc.writeCommitGraph=true` enables writing the commit-graph file during
-garbage collection.
\ No newline at end of file
+garbage collection.
+
+feature.manyFiles::
+	Enable config options that optimize for repos with many files in the
+	working directory. With many files, commands such as `git status` and
+	`git checkout` may be slow and these new defaults improve performance:
++
+* `index.version=4` enables path-prefix compression in the index.
++
+* `core.untrackedCache=true` enables the untracked cache. This setting assumes
+that mtime is working on your machine.
\ No newline at end of file
diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
index f181503041..7cb50b37e9 100644
--- a/Documentation/config/index.txt
+++ b/Documentation/config/index.txt
@@ -24,3 +24,4 @@ index.threads::
 index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.
+	If `feature.manyFiles` is enabled, then the default is 4.
diff --git a/repo-settings.c b/repo-settings.c
index 9ed83e6e54..af93696343 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -42,6 +42,10 @@ void prepare_repo_settings(struct repository *r)
 		UPDATE_DEFAULT(r->settings.core_commit_graph, 1);
 		UPDATE_DEFAULT(r->settings.gc_write_commit_graph, 1);
 	}
+	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
+		UPDATE_DEFAULT(r->settings.index_version, 4);
+		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
+	}
 
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
diff --git a/t/t1600-index.sh b/t/t1600-index.sh
index 42962ed7d4..c77721b580 100755
--- a/t/t1600-index.sh
+++ b/t/t1600-index.sh
@@ -59,17 +59,38 @@ test_expect_success 'out of bounds index.version issues warning' '
 	)
 '
 
-test_expect_success 'GIT_INDEX_VERSION takes precedence over config' '
+test_index_version () {
+	INDEX_VERSION_CONFIG=$1 &&
+	FEATURE_MANY_FILES=$2 &&
+	ENV_VAR_VERSION=$3
+	EXPECTED_OUTPUT_VERSION=$4 &&
 	(
 		rm -f .git/index &&
-		GIT_INDEX_VERSION=4 &&
-		export GIT_INDEX_VERSION &&
-		git config --add index.version 2 &&
+		rm -f .git/config &&
+		if test "$INDEX_VERSION_CONFIG" -ne 0
+		then
+			git config --add index.version $INDEX_VERSION_CONFIG
+		fi &&
+		git config --add feature.manyFiles $FEATURE_MANY_FILES
+		if test "$ENV_VAR_VERSION" -ne 0
+		then
+			GIT_INDEX_VERSION=$ENV_VAR_VERSION &&
+			export GIT_INDEX_VERSION
+		else
+			unset GIT_INDEX_VERSION
+		fi &&
 		git add a 2>&1 &&
-		echo 4 >expect &&
+		echo $EXPECTED_OUTPUT_VERSION >expect &&
 		test-tool index-version <.git/index >actual &&
 		test_cmp expect actual
 	)
+}
+
+test_expect_success 'index version config precedence' '
+	test_index_version 2 false 4 4 &&
+	test_index_version 2 true 0 2 &&
+	test_index_version 0 true 0 4 &&
+	test_index_version 0 true 2 2
 '
 
 test_done

Documentation/config/feature.txt, Documentation/config/fetch.txt, Documentation/config/merge.txt, Documentation/config/pack.txt, fetch-negotiator.c, fetch-negotiator.h, fetch-pack.c, merge-recursive.c, repo-settings.c, repository.h, t/t5552-skipping-fetch-negotiator.sh

diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index c2d9ef7473..287621b1e8 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -4,6 +4,23 @@ feature.*::
 	developer community as recommended defaults and are subject to change.
 	In particular, new config options may be added with different defaults.
 
+feature.experimental::
+	Enable config options that are new to Git, and are being considered for
+	future defaults. Config settings included here may be added or removed
+	with each release, including minor version updates. These settings may
+	have unintended interactions since they are so new. Please enable this
+	setting if you are interested in providing feedback on experimental
+	features. The new default values are:
++
+* `pack.useSparse=true` uses a new algorithm when constructing a pack-file
+which can improve `git push` performance in repos with many files.
++
+* `merge.directoryRenames=true` uses a new algorithm for detecting renames by
+using entire directories at a time instead of single files at a time.
++
+* `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
+skipping more commits at a time, reducing the number of round trips.
+
 feature.manyCommits::
 	Enable config options that optimize for repos with many commits. This
 	setting is recommended for repos with at least 100,000 commits. The
diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
index ba890b5884..d402110638 100644
--- a/Documentation/config/fetch.txt
+++ b/Documentation/config/fetch.txt
@@ -59,7 +59,8 @@ fetch.negotiationAlgorithm::
 	effort to converge faster, but may result in a larger-than-necessary
 	packfile; The default is "default" which instructs Git to use the default algorithm
 	that never skips commits (unless the server has acknowledged it or one
-	of its descendants).
+	of its descendants). If `feature.experimental` is enabled, then this
+	setting defaults to "skipping".
 	Unknown values will cause 'git fetch' to error out.
 +
 See also the `--negotiation-tip` option for linkgit:git-fetch[1].
diff --git a/Documentation/config/merge.txt b/Documentation/config/merge.txt
index 6a313937f8..e8def2d63c 100644
--- a/Documentation/config/merge.txt
+++ b/Documentation/config/merge.txt
@@ -54,7 +54,8 @@ merge.directoryRenames::
 	moved into the new directory.  If set to "conflict", a conflict
 	will be reported for such paths.  If merge.renames is false,
 	merge.directoryRenames is ignored and treated as false.  Defaults
-	to "conflict".
+	to "conflict" unless `feature.experimental` is enabled and the
+	default is "true".
 
 merge.renormalize::
 	Tell Git that canonical representation of files in the
diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index 9cdcfa7324..1d66f0c992 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -112,7 +112,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames.
+	commits contain certain types of direct renames. Default is `false`
+	unless `feature.experimental` is enabled.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.
diff --git a/fetch-negotiator.c b/fetch-negotiator.c
index d6d685cba0..0a1357dc9d 100644
--- a/fetch-negotiator.c
+++ b/fetch-negotiator.c
@@ -2,19 +2,20 @@
 #include "fetch-negotiator.h"
 #include "negotiator/default.h"
 #include "negotiator/skipping.h"
+#include "repository.h"
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm)
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator)
 {
-	if (algorithm) {
-		if (!strcmp(algorithm, "skipping")) {
-			skipping_negotiator_init(negotiator);
-			return;
-		} else if (!strcmp(algorithm, "default")) {
-			/* Fall through to default initialization */
-		} else {
-			die("unknown fetch negotiation algorithm '%s'", algorithm);
-		}
+	prepare_repo_settings(r);
+	switch(r->settings.fetch_negotiation_algorithm) {
+	case FETCH_NEGOTIATION_SKIPPING:
+		skipping_negotiator_init(negotiator);
+		return;
+
+	case FETCH_NEGOTIATION_DEFAULT:
+	default:
+		default_negotiator_init(negotiator);
+		return;
 	}
-	default_negotiator_init(negotiator);
 }
diff --git a/fetch-negotiator.h b/fetch-negotiator.h
index 9e3967ce66..ea78868504 100644
--- a/fetch-negotiator.h
+++ b/fetch-negotiator.h
@@ -2,6 +2,7 @@
 #define FETCH_NEGOTIATOR_H
 
 struct commit;
+struct repository;
 
 /*
  * An object that supplies the information needed to negotiate the contents of
@@ -52,7 +53,7 @@ struct fetch_negotiator {
 	void *data;
 };
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm);
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator);
 
 #endif
diff --git a/fetch-pack.c b/fetch-pack.c
index 65be043f2a..d81f47c07b 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -36,7 +36,6 @@ static int agent_supported;
 static int server_supports_filtering;
 static struct lock_file shallow_lock;
 static const char *alternate_shallow_file;
-static char *negotiation_algorithm;
 static struct strbuf fsck_msg_types = STRBUF_INIT;
 
 /* Remember to update object flag allocation in object.h */
@@ -892,12 +891,13 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 				 struct shallow_info *si,
 				 char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	struct object_id oid;
 	const char *agent_feature;
 	int agent_len;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 
 	sort_ref_list(&ref, ref_compare_name);
 	QSORT(sought, nr_sought, cmp_ref_by_name);
@@ -911,7 +911,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 
 	if (server_supports("shallow"))
 		print_verbose(args, _("Server supports %s"), "shallow");
-	else if (args->depth > 0 || is_repository_shallow(the_repository))
+	else if (args->depth > 0 || is_repository_shallow(r))
 		die(_("Server does not support shallow clients"));
 	if (args->depth > 0 || args->deepen_since || args->deepen_not)
 		args->deepen = 1;
@@ -1379,6 +1379,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				    struct shallow_info *si,
 				    char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	enum fetch_state state = FETCH_CHECK_LOCAL;
 	struct oidset common = OIDSET_INIT;
@@ -1386,7 +1387,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	int in_vain = 0;
 	int haves_to_send = INITIAL_FLUSH;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 	packet_reader_init(&reader, fd[0], NULL, 0,
 			   PACKET_READ_CHOMP_NEWLINE |
 			   PACKET_READ_DIE_ON_ERR_PACKET);
@@ -1505,8 +1506,6 @@ static void fetch_pack_config(void)
 	git_config_get_bool("repack.usedeltabaseoffset", &prefer_ofs_delta);
 	git_config_get_bool("fetch.fsckobjects", &fetch_fsck_objects);
 	git_config_get_bool("transfer.fsckobjects", &transfer_fsck_objects);
-	git_config_get_string("fetch.negotiationalgorithm",
-			      &negotiation_algorithm);
 
 	git_config(fetch_pack_config_cb, NULL);
 }
diff --git a/merge-recursive.c b/merge-recursive.c
index 12300131fc..4f77b4b3bb 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3662,15 +3662,6 @@ static void merge_recursive_config(struct merge_options *opt)
 		opt->merge_detect_rename = git_config_rename("merge.renames", value);
 		free(value);
 	}
-	if (!git_config_get_string("merge.directoryrenames", &value)) {
-		int boolval = git_parse_maybe_bool(value);
-		if (0 <= boolval) {
-			opt->detect_directory_renames = boolval ? 2 : 0;
-		} else if (!strcasecmp(value, "conflict")) {
-			opt->detect_directory_renames = 1;
-		} /* avoid erroring on values from future versions of git */
-		free(value);
-	}
 	git_config(git_xmerge_config, NULL);
 }
 
@@ -3688,6 +3679,11 @@ void init_merge_options(struct merge_options *opt,
 	opt->diff_detect_rename = -1;
 	opt->merge_detect_rename = -1;
 	opt->detect_directory_renames = 1;
+
+	prepare_repo_settings(repo);
+	if (repo->settings.merge_directory_renames >= 0)
+		opt->detect_directory_renames = repo->settings.merge_directory_renames;
+
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/repo-settings.c b/repo-settings.c
index af93696343..e0673938c0 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -34,6 +34,18 @@ void prepare_repo_settings(struct repository *r)
 		free(strval);
 	}
 
+	if (!repo_config_get_maybe_bool(r, "merge.directoryrenames", &value))
+		r->settings.merge_directory_renames = value ? MERGE_DIRECTORY_RENAMES_TRUE : 0;
+	else if (!repo_config_get_string(r, "merge.directoryrenames", &strval)) {
+		if (!strcasecmp(strval, "conflict"))
+			r->settings.merge_directory_renames = MERGE_DIRECTORY_RENAMES_CONFLICT;
+	}
+	if (!repo_config_get_string(r, "fetch.negotiationalgorithm", &strval)) {
+		if (!strcasecmp(strval, "skipping"))
+			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
+		else
+			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_DEFAULT;
+	}
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
@@ -46,6 +58,11 @@ void prepare_repo_settings(struct repository *r)
 		UPDATE_DEFAULT(r->settings.index_version, 4);
 		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
 	}
+	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
+		UPDATE_DEFAULT(r->settings.pack_use_sparse, 1);
+		UPDATE_DEFAULT(r->settings.merge_directory_renames, MERGE_DIRECTORY_RENAMES_TRUE);
+		UPDATE_DEFAULT(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
+	}
 
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
@@ -53,4 +70,6 @@ void prepare_repo_settings(struct repository *r)
 	else
 		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
 
+	UPDATE_DEFAULT(r->settings.merge_directory_renames, MERGE_DIRECTORY_RENAMES_CONFLICT);
+	UPDATE_DEFAULT(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_DEFAULT);
 }
diff --git a/repository.h b/repository.h
index e7a72e2341..b8e52dd48f 100644
--- a/repository.h
+++ b/repository.h
@@ -19,6 +19,20 @@ enum untracked_cache_setting {
 	UNTRACKED_CACHE_WRITE = 2
 };
 
+enum merge_directory_renames_setting {
+	MERGE_DIRECTORY_RENAMES_UNSET = -1,
+	MERGE_DIRECTORY_RENAMES_NONE = 0,
+	MERGE_DIRECTORY_RENAMES_CONFLICT = 1,
+	MERGE_DIRECTORY_RENAMES_TRUE = 2,
+};
+
+enum fetch_negotiation_setting {
+	FETCH_NEGOTIATION_UNSET = -1,
+	FETCH_NEGOTIATION_NONE = 0,
+	FETCH_NEGOTIATION_DEFAULT = 1,
+	FETCH_NEGOTIATION_SKIPPING = 2,
+};
+
 struct repo_settings {
 	int initialized;
 
@@ -29,6 +43,8 @@ struct repo_settings {
 	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
+	enum merge_directory_renames_setting merge_directory_renames;
+	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 };
 
 struct repository {
diff --git a/t/t5552-skipping-fetch-negotiator.sh b/t/t5552-skipping-fetch-negotiator.sh
index 8a14be51a1..f70cbcc9ca 100755
--- a/t/t5552-skipping-fetch-negotiator.sh
+++ b/t/t5552-skipping-fetch-negotiator.sh
@@ -60,29 +60,6 @@ test_expect_success 'commits with no parents are sent regardless of skip distanc
 	have_not_sent c6 c4 c3
 '
 
-test_expect_success 'unknown fetch.negotiationAlgorithm values error out' '
-	rm -rf server client trace &&
-	git init server &&
-	test_commit -C server to_fetch &&
-
-	git init client &&
-	test_commit -C client on_client &&
-	git -C client checkout on_client &&
-
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	test_must_fail git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep "unknown fetch negotiation algorithm" err &&
-
-	# Explicit "default" value
-	test_config -C client fetch.negotiationAlgorithm default &&
-	git -C client -c fetch.negotiationAlgorithm=default fetch "$(pwd)/server" &&
-
-	# Implementation detail: If there is nothing to fetch, we will not error out
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep ! "unknown fetch negotiation algorithm" err
-'
-
 test_expect_success 'when two skips collide, favor the larger one' '
 	rm -rf server client trace &&
 	git init server &&

builtin/update-index.c, config.c, read-cache.c, repo-settings.c, repository.h

diff --git a/builtin/update-index.c b/builtin/update-index.c
index dff2f4b837..49302d98c5 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -966,6 +966,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	struct parse_opt_ctx_t ctx;
 	strbuf_getline_fn getline_fn;
 	int parseopt_state = PARSE_OPT_UNKNOWN;
+	struct repository *r = the_repository;
 	struct option options[] = {
 		OPT_BIT('q', NULL, &refresh_args.flags,
 			N_("continue refresh even when index needs update"),
@@ -1180,11 +1181,12 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		remove_split_index(&the_index);
 	}
 
+	prepare_repo_settings(r);
 	switch (untracked_cache) {
 	case UC_UNSPECIFIED:
 		break;
 	case UC_DISABLE:
-		if (git_config_get_untracked_cache() == 1)
+		if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
 			warning(_("core.untrackedCache is set to true; "
 				  "remove or change it, if you really want to "
 				  "disable the untracked cache"));
@@ -1196,7 +1198,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		return !test_if_untracked_cache_is_supported();
 	case UC_ENABLE:
 	case UC_FORCE:
-		if (git_config_get_untracked_cache() == 0)
+		if (r->settings.core_untracked_cache == UNTRACKED_CACHE_REMOVE)
 			warning(_("core.untrackedCache is set to false; "
 				  "remove or change it, if you really want to "
 				  "enable the untracked cache"));
diff --git a/config.c b/config.c
index faa57e436c..3241dbc54d 100644
--- a/config.c
+++ b/config.c
@@ -2277,30 +2277,6 @@ int git_config_get_expiry_in_days(const char *key, timestamp_t *expiry, timestam
 	return -1; /* thing exists but cannot be parsed */
 }
 
-int git_config_get_untracked_cache(void)
-{
-	int val = -1;
-	const char *v;
-
-	/* Hack for test programs like test-dump-untracked-cache */
-	if (ignore_untracked_cache_config)
-		return -1;
-
-	if (!git_config_get_maybe_bool("core.untrackedcache", &val))
-		return val;
-
-	if (!git_config_get_value("core.untrackedcache", &v)) {
-		if (!strcasecmp(v, "keep"))
-			return -1;
-
-		error(_("unknown core.untrackedCache value '%s'; "
-			"using 'keep' default value"), v);
-		return -1;
-	}
-
-	return -1; /* default value */
-}
-
 int git_config_get_split_index(void)
 {
 	int val;
diff --git a/read-cache.c b/read-cache.c
index 59dbebc15d..7a07286164 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1845,18 +1845,17 @@ static void check_ce_order(struct index_state *istate)
 
 static void tweak_untracked_cache(struct index_state *istate)
 {
-	switch (git_config_get_untracked_cache()) {
-	case -1: /* keep: do nothing */
-		break;
-	case 0: /* false */
+	struct repository *r = the_repository;
+
+	prepare_repo_settings(r);
+
+	if (r->settings.core_untracked_cache  == UNTRACKED_CACHE_REMOVE) {
 		remove_untracked_cache(istate);
-		break;
-	case 1: /* true */
-		add_untracked_cache(istate);
-		break;
-	default: /* unknown value: do nothing */
-		break;
+		return;
 	}
+
+	if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
+		add_untracked_cache(istate);
 }
 
 static void tweak_split_index(struct index_state *istate)
diff --git a/repo-settings.c b/repo-settings.c
index fc05f4fbc4..9ed83e6e54 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -7,6 +7,7 @@
 void prepare_repo_settings(struct repository *r)
 {
 	int value;
+	char *strval;
 
 	if (r->settings.initialized)
 		return;
@@ -21,12 +22,31 @@ void prepare_repo_settings(struct repository *r)
 
 	if (!repo_config_get_bool(r, "index.version", &value))
 		r->settings.index_version = value;
+	if (!repo_config_get_maybe_bool(r, "core.untrackedcache", &value)) {
+		if (value == 0)
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_REMOVE;
+		else
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_WRITE;
+	} else if (!repo_config_get_string(r, "core.untrackedcache", &strval)) {
+		if (!strcasecmp(strval, "keep"))
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
+
+		free(strval);
+	}
+
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
-
+	
 	if (!repo_config_get_bool(r, "feature.manycommits", &value) && value) {
 		UPDATE_DEFAULT(r->settings.core_commit_graph, 1);
 		UPDATE_DEFAULT(r->settings.gc_write_commit_graph, 1);
 	}
+
+	/* Hack for test programs like test-dump-untracked-cache */
+	if (ignore_untracked_cache_config)
+		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
+	else
+		UPDATE_DEFAULT(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
+
 }
diff --git a/repository.h b/repository.h
index 2bb2bc3eea..e7a72e2341 100644
--- a/repository.h
+++ b/repository.h
@@ -12,6 +12,13 @@ struct pathspec;
 struct raw_object_store;
 struct submodule_cache;
 
+enum untracked_cache_setting {
+	UNTRACKED_CACHE_UNSET = -1,
+	UNTRACKED_CACHE_REMOVE = 0,
+	UNTRACKED_CACHE_KEEP = 1,
+	UNTRACKED_CACHE_WRITE = 2
+};
+
 struct repo_settings {
 	int initialized;
 
@@ -19,6 +26,7 @@ struct repo_settings {
 	int gc_write_commit_graph;
 
 	int index_version;
+	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
 };

diff --git a/t/t6501-freshen-objects.sh b/t/t6501-freshen-objects.sh
index 033871ee5f..f30b4849b6 100755
--- a/t/t6501-freshen-objects.sh
+++ b/t/t6501-freshen-objects.sh
@@ -137,7 +137,7 @@ test_expect_success 'do not complain about existing broken links (commit)' '
 	some message
 	EOF
 	commit=$(git hash-object -t commit -w broken-commit) &&
-	git gc 2>stderr &&
+	git gc -q 2>stderr &&
 	verbose git cat-file -e $commit &&
 	test_must_be_empty stderr
 '
@@ -147,7 +147,7 @@ test_expect_success 'do not complain about existing broken links (tree)' '
 	100644 blob 0000000000000000000000000000000000000003	foo
 	EOF
 	tree=$(git mktree --missing <broken-tree) &&
-	git gc 2>stderr &&
+	git gc -q 2>stderr &&
 	git cat-file -e $tree &&
 	test_must_be_empty stderr
 '
@@ -162,7 +162,7 @@ test_expect_success 'do not complain about existing broken links (tag)' '
 	this is a broken tag
 	EOF
 	tag=$(git hash-object -t tag -w broken-tag) &&
-	git gc 2>stderr &&
+	git gc -q 2>stderr &&
 	git cat-file -e $tag &&
 	test_must_be_empty stderr
 '

Makefile, builtin/gc.c, builtin/pack-objects.c, commit-graph.c, read-cache.c, repo-settings.c, repository.h

diff --git a/Makefile b/Makefile
index 11ccea4071..032fe9b5f9 100644
--- a/Makefile
+++ b/Makefile
@@ -964,6 +964,7 @@ LIB_OBJS += refspec.o
 LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace-object.o
+LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
 LIB_OBJS += resolve-undo.o
diff --git a/builtin/gc.c b/builtin/gc.c
index c18efadda5..4b8fbb9965 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -41,7 +41,6 @@ static int aggressive_depth = 50;
 static int aggressive_window = 250;
 static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
-static int gc_write_commit_graph;
 static int detach_auto = 1;
 static timestamp_t gc_log_expire_time;
 static const char *gc_log_expire = "1.day.ago";
@@ -148,7 +147,6 @@ static void gc_config(void)
 	git_config_get_int("gc.aggressivedepth", &aggressive_depth);
 	git_config_get_int("gc.auto", &gc_auto_threshold);
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
-	git_config_get_bool("gc.writecommitgraph", &gc_write_commit_graph);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_get_expiry("gc.pruneexpire", &prune_expire);
 	git_config_get_expiry("gc.worktreepruneexpire", &prune_worktrees_expire);
@@ -685,11 +683,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		clean_pack_garbage();
 	}
 
-	if (gc_write_commit_graph &&
-	    write_commit_graph_reachable(get_object_directory(),
-					 !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
-					 NULL))
-		return 1;
+	prepare_repo_settings(the_repository);
+	if (the_repository->settings.gc_write_commit_graph == 1)
+		write_commit_graph_reachable(get_object_directory(),
+					     !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
+					     NULL);
 
 	if (auto_gc && too_many_loose_objects())
 		warning(_("There are too many unreachable loose objects; "
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 267c562b1f..f9f7181f3f 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2709,10 +2709,6 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(k, "pack.usesparse")) {
-		sparse = git_config_bool(k, v);
-		return 0;
-	}
 	if (!strcmp(k, "pack.threads")) {
 		delta_search_threads = git_config_int(k, v);
 		if (delta_search_threads < 0)
@@ -3332,6 +3328,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	read_replace_refs = 0;
 
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
+	prepare_repo_settings(the_repository);
+	if (!sparse && the_repository->settings.pack_use_sparse != -1)
+		sparse = the_repository->settings.pack_use_sparse;
+
 	reset_pack_idx_option(&pack_idx_opts);
 	git_config(git_pack_config, NULL);
 
diff --git a/commit-graph.c b/commit-graph.c
index b3c4de79b6..7854e491b2 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -466,7 +466,6 @@ static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
 static int prepare_commit_graph(struct repository *r)
 {
 	struct object_directory *odb;
-	int config_value;
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
 		die("dying as requested by the '%s' variable on commit-graph load!",
@@ -476,9 +475,10 @@ static int prepare_commit_graph(struct repository *r)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
+	prepare_repo_settings(r);
+
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
-	    (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
-	    !config_value))
+	    r->settings.core_commit_graph != 1)
 		/*
 		 * This repository is not configured to use commit graphs, so
 		 * do not load one. (But report commit_graph_attempted anyway
diff --git a/read-cache.c b/read-cache.c
index c701f7f8b8..59dbebc15d 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1599,16 +1599,17 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
 
 #define INDEX_FORMAT_DEFAULT 3
 
-static unsigned int get_index_format_default(void)
+static unsigned int get_index_format_default(struct repository *r)
 {
 	char *envversion = getenv("GIT_INDEX_VERSION");
 	char *endp;
-	int value;
 	unsigned int version = INDEX_FORMAT_DEFAULT;
 
 	if (!envversion) {
-		if (!git_config_get_int("index.version", &value))
-			version = value;
+		prepare_repo_settings(r);
+
+		if (r->settings.index_version >= 0)
+			version = r->settings.index_version;
 		if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
 			warning(_("index.version set, but the value is invalid.\n"
 				  "Using version %i"), INDEX_FORMAT_DEFAULT);
@@ -2765,7 +2766,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	}
 
 	if (!istate->version) {
-		istate->version = get_index_format_default();
+		istate->version = get_index_format_default(the_repository);
 		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}
diff --git a/repo-settings.c b/repo-settings.c
new file mode 100644
index 0000000000..309577f6bc
--- /dev/null
+++ b/repo-settings.c
@@ -0,0 +1,25 @@
+#include "cache.h"
+#include "config.h"
+#include "repository.h"
+
+void prepare_repo_settings(struct repository *r)
+{
+	int value;
+
+	if (r->settings.initialized)
+		return;
+
+	/* Defaults */
+	memset(&r->settings, -1, sizeof(r->settings));
+
+	if (!repo_config_get_bool(r, "core.commitgraph", &value))
+		r->settings.core_commit_graph = value;
+	if (!repo_config_get_bool(r, "gc.writecommitgraph", &value))
+		r->settings.gc_write_commit_graph = value;
+
+	if (!repo_config_get_bool(r, "index.version", &value))
+		r->settings.index_version = value;
+
+	if (!repo_config_get_bool(r, "pack.usesparse", &value))
+		r->settings.pack_use_sparse = value;
+}
diff --git a/repository.h b/repository.h
index 4fb6a5885f..cc285ad327 100644
--- a/repository.h
+++ b/repository.h
@@ -11,6 +11,17 @@ struct pathspec;
 struct raw_object_store;
 struct submodule_cache;
 
+struct repo_settings {
+	int initialized;
+
+	int core_commit_graph;
+	int gc_write_commit_graph;
+
+	int index_version;
+
+	int pack_use_sparse;
+};
+
 struct repository {
 	/* Environment */
 	/*
@@ -72,6 +83,8 @@ struct repository {
 	 */
 	char *submodule_prefix;
 
+	struct repo_settings settings;
+
 	/* Subsystems */
 	/*
 	 * Repository's config which contains key-value pairs from the usual
@@ -157,5 +170,6 @@ int repo_read_index_unmerged(struct repository *);
  */
 void repo_update_index_if_able(struct repository *, struct lock_file *);
 
+void prepare_repo_settings(struct repository *r);
 
 #endif /* REPOSITORY_H */

builtin/update-index.c, config.c, read-cache.c, repo-settings.c, repository.h

diff --git a/builtin/update-index.c b/builtin/update-index.c
index dff2f4b837..49302d98c5 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -966,6 +966,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	struct parse_opt_ctx_t ctx;
 	strbuf_getline_fn getline_fn;
 	int parseopt_state = PARSE_OPT_UNKNOWN;
+	struct repository *r = the_repository;
 	struct option options[] = {
 		OPT_BIT('q', NULL, &refresh_args.flags,
 			N_("continue refresh even when index needs update"),
@@ -1180,11 +1181,12 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		remove_split_index(&the_index);
 	}
 
+	prepare_repo_settings(r);
 	switch (untracked_cache) {
 	case UC_UNSPECIFIED:
 		break;
 	case UC_DISABLE:
-		if (git_config_get_untracked_cache() == 1)
+		if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
 			warning(_("core.untrackedCache is set to true; "
 				  "remove or change it, if you really want to "
 				  "disable the untracked cache"));
@@ -1196,7 +1198,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		return !test_if_untracked_cache_is_supported();
 	case UC_ENABLE:
 	case UC_FORCE:
-		if (git_config_get_untracked_cache() == 0)
+		if (r->settings.core_untracked_cache == UNTRACKED_CACHE_REMOVE)
 			warning(_("core.untrackedCache is set to false; "
 				  "remove or change it, if you really want to "
 				  "enable the untracked cache"));
diff --git a/config.c b/config.c
index faa57e436c..3241dbc54d 100644
--- a/config.c
+++ b/config.c
@@ -2277,30 +2277,6 @@ int git_config_get_expiry_in_days(const char *key, timestamp_t *expiry, timestam
 	return -1; /* thing exists but cannot be parsed */
 }
 
-int git_config_get_untracked_cache(void)
-{
-	int val = -1;
-	const char *v;
-
-	/* Hack for test programs like test-dump-untracked-cache */
-	if (ignore_untracked_cache_config)
-		return -1;
-
-	if (!git_config_get_maybe_bool("core.untrackedcache", &val))
-		return val;
-
-	if (!git_config_get_value("core.untrackedcache", &v)) {
-		if (!strcasecmp(v, "keep"))
-			return -1;
-
-		error(_("unknown core.untrackedCache value '%s'; "
-			"using 'keep' default value"), v);
-		return -1;
-	}
-
-	return -1; /* default value */
-}
-
 int git_config_get_split_index(void)
 {
 	int val;
diff --git a/read-cache.c b/read-cache.c
index 59dbebc15d..7a07286164 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1845,18 +1845,17 @@ static void check_ce_order(struct index_state *istate)
 
 static void tweak_untracked_cache(struct index_state *istate)
 {
-	switch (git_config_get_untracked_cache()) {
-	case -1: /* keep: do nothing */
-		break;
-	case 0: /* false */
+	struct repository *r = the_repository;
+
+	prepare_repo_settings(r);
+
+	if (r->settings.core_untracked_cache  == UNTRACKED_CACHE_REMOVE) {
 		remove_untracked_cache(istate);
-		break;
-	case 1: /* true */
-		add_untracked_cache(istate);
-		break;
-	default: /* unknown value: do nothing */
-		break;
+		return;
 	}
+
+	if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
+		add_untracked_cache(istate);
 }
 
 static void tweak_split_index(struct index_state *istate)
diff --git a/repo-settings.c b/repo-settings.c
index d00b675687..abbc6566f8 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -7,6 +7,7 @@
 void prepare_repo_settings(struct repository *r)
 {
 	int value;
+	char *strval;
 
 	if (r->settings.initialized)
 		return;
@@ -23,7 +24,25 @@ void prepare_repo_settings(struct repository *r)
 
 	if (!repo_config_get_bool(r, "index.version", &value))
 		r->settings.index_version = value;
+	if (!repo_config_get_maybe_bool(r, "core.untrackedcache", &value)) {
+		if (value == 0)
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_REMOVE;
+		else
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_WRITE;
+	} else if (!repo_config_get_string(r, "core.untrackedcache", &strval)) {
+		if (!strcasecmp(strval, "keep"))
+			r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
+
+		free(strval);
+	}
+
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
+
+	/* Hack for test programs like test-dump-untracked-cache */
+	if (ignore_untracked_cache_config)
+		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
+	else
+		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
 }
diff --git a/repository.h b/repository.h
index cc285ad327..cf7ff0778c 100644
--- a/repository.h
+++ b/repository.h
@@ -11,6 +11,13 @@ struct pathspec;
 struct raw_object_store;
 struct submodule_cache;
 
+enum untracked_cache_setting {
+	UNTRACKED_CACHE_UNSET = -1,
+	UNTRACKED_CACHE_REMOVE = 0,
+	UNTRACKED_CACHE_KEEP = 1,
+	UNTRACKED_CACHE_WRITE = 2
+};
+
 struct repo_settings {
 	int initialized;
 
@@ -18,6 +25,7 @@ struct repo_settings {
 	int gc_write_commit_graph;
 
 	int index_version;
+	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
 };

Documentation/config.txt, Documentation/config/core.txt, Documentation/config/feature.txt, Documentation/config/index.txt, repo-settings.c, t/t1600-index.sh

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e3f5bc3396..77f3b1486b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -345,6 +345,8 @@ include::config/difftool.txt[]
 
 include::config/fastimport.txt[]
 
+include::config/feature.txt[]
+
 include::config/fetch.txt[]
 
 include::config/format.txt[]
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index e66d79fd76..852d2ba37a 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -86,7 +86,9 @@ core.untrackedCache::
 	it will automatically be removed, if set to `false`. Before
 	setting it to `true`, you should check that mtime is working
 	properly on your system.
-	See linkgit:git-update-index[1]. `keep` by default.
+	See linkgit:git-update-index[1]. `keep` by default, unless
+	`feature.manyFiles` is enabled which sets this setting to
+	`true` by default.
 
 core.checkStat::
 	When missing or is set to `default`, many fields in the stat
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
new file mode 100644
index 0000000000..8ea198a642
--- /dev/null
+++ b/Documentation/config/feature.txt
@@ -0,0 +1,15 @@
+feature.*::
+	The config settings that start with `feature.` modify the defaults of
+	a group of other config settings. These groups are created by the Git
+	developer community as recommended defaults and are subject to change.
+	In particular, new config options may be added with different defaults.
+
+feature.manyFiles::
+	Enable config options that optimize for repos with many files in the
+	working directory. With many files, commands such as `git status` and
+	`git checkout` may be slow and these new defaults improve performance:
++
+* `index.version=4` enables path-prefix compression in the index.
++
+* `core.untrackedCache=true` enables the untracked cache. This setting assumes
+that mtime is working on your machine.
diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
index f181503041..7cb50b37e9 100644
--- a/Documentation/config/index.txt
+++ b/Documentation/config/index.txt
@@ -24,3 +24,4 @@ index.threads::
 index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.
+	If `feature.manyFiles` is enabled, then the default is 4.
diff --git a/repo-settings.c b/repo-settings.c
index abbc6566f8..d5bf9069f4 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -36,9 +36,12 @@ void prepare_repo_settings(struct repository *r)
 		free(strval);
 	}
 
-
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
+	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
+		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
+		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
+	}
 
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
diff --git a/t/t1600-index.sh b/t/t1600-index.sh
index 42962ed7d4..c77721b580 100755
--- a/t/t1600-index.sh
+++ b/t/t1600-index.sh
@@ -59,17 +59,38 @@ test_expect_success 'out of bounds index.version issues warning' '
 	)
 '
 
-test_expect_success 'GIT_INDEX_VERSION takes precedence over config' '
+test_index_version () {
+	INDEX_VERSION_CONFIG=$1 &&
+	FEATURE_MANY_FILES=$2 &&
+	ENV_VAR_VERSION=$3
+	EXPECTED_OUTPUT_VERSION=$4 &&
 	(
 		rm -f .git/index &&
-		GIT_INDEX_VERSION=4 &&
-		export GIT_INDEX_VERSION &&
-		git config --add index.version 2 &&
+		rm -f .git/config &&
+		if test "$INDEX_VERSION_CONFIG" -ne 0
+		then
+			git config --add index.version $INDEX_VERSION_CONFIG
+		fi &&
+		git config --add feature.manyFiles $FEATURE_MANY_FILES
+		if test "$ENV_VAR_VERSION" -ne 0
+		then
+			GIT_INDEX_VERSION=$ENV_VAR_VERSION &&
+			export GIT_INDEX_VERSION
+		else
+			unset GIT_INDEX_VERSION
+		fi &&
 		git add a 2>&1 &&
-		echo 4 >expect &&
+		echo $EXPECTED_OUTPUT_VERSION >expect &&
 		test-tool index-version <.git/index >actual &&
 		test_cmp expect actual
 	)
+}
+
+test_expect_success 'index version config precedence' '
+	test_index_version 2 false 4 4 &&
+	test_index_version 2 true 0 2 &&
+	test_index_version 0 true 0 4 &&
+	test_index_version 0 true 2 2
 '
 
 test_done

Documentation/config/core.txt, Documentation/config/gc.txt, repo-settings.c, t/t0410-partial-clone.sh, t/t5307-pack-missing-commit.sh, t/t5324-split-commit-graph.sh, t/t6011-rev-list-with-bad-commit.sh

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 75538d27e7..e66d79fd76 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -577,7 +577,7 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to true. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 02b92b18b5..00ea0a678e 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -63,7 +63,7 @@ gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
 	linkgit:git-gc[1] is run. When using `git gc --auto`
 	the commit-graph will be updated if housekeeping is
-	required. Default is false. See linkgit:git-commit-graph[1]
+	required. Default is true. See linkgit:git-commit-graph[1]
 	for details.
 
 gc.logExpiry::
diff --git a/repo-settings.c b/repo-settings.c
index 309577f6bc..d00b675687 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -2,6 +2,8 @@
 #include "config.h"
 #include "repository.h"
 
+#define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
+
 void prepare_repo_settings(struct repository *r)
 {
 	int value;
@@ -16,6 +18,8 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.core_commit_graph = value;
 	if (!repo_config_get_bool(r, "gc.writecommitgraph", &value))
 		r->settings.gc_write_commit_graph = value;
+	UPDATE_DEFAULT_BOOL(r->settings.core_commit_graph, 1);
+	UPDATE_DEFAULT_BOOL(r->settings.gc_write_commit_graph, 1);
 
 	if (!repo_config_get_bool(r, "index.version", &value))
 		r->settings.index_version = value;
diff --git a/t/t0410-partial-clone.sh b/t/t0410-partial-clone.sh
index 5bd892f2f7..181ffa44e9 100755
--- a/t/t0410-partial-clone.sh
+++ b/t/t0410-partial-clone.sh
@@ -234,7 +234,7 @@ test_expect_success 'rev-list stops traversal at missing and promised commit' '
 
 	git -C repo config core.repositoryformatversion 1 &&
 	git -C repo config extensions.partialclone "arbitrary string" &&
-	GIT_TEST_COMMIT_GRAPH=0 git -C repo rev-list --exclude-promisor-objects --objects bar >out &&
+	GIT_TEST_COMMIT_GRAPH=0 git -C repo -c core.commitGraph=false rev-list --exclude-promisor-objects --objects bar >out &&
 	grep $(git -C repo rev-parse bar) out &&
 	! grep $FOO out
 '
diff --git a/t/t5307-pack-missing-commit.sh b/t/t5307-pack-missing-commit.sh
index dacb440b27..f4338abb78 100755
--- a/t/t5307-pack-missing-commit.sh
+++ b/t/t5307-pack-missing-commit.sh
@@ -24,11 +24,11 @@ test_expect_success 'check corruption' '
 '
 
 test_expect_success 'rev-list notices corruption (1)' '
-	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git rev-list HEAD
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git -c core.commitGraph=false rev-list HEAD
 '
 
 test_expect_success 'rev-list notices corruption (2)' '
-	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git rev-list --objects HEAD
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git -c core.commitGraph=false rev-list --objects HEAD
 '
 
 test_expect_success 'pack-objects notices corruption' '
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 03f45a1ed9..19aa40de15 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -8,6 +8,7 @@ GIT_TEST_COMMIT_GRAPH=0
 test_expect_success 'setup repo' '
 	git init &&
 	git config core.commitGraph true &&
+	git config gc.writeCommitGraph false &&
 	infodir=".git/objects/info" &&
 	graphdir="$infodir/commit-graphs" &&
 	test_oid_init
@@ -332,6 +333,7 @@ test_expect_success 'split across alternate where alternate is not split' '
 	git clone --no-hardlinks . alt-split &&
 	(
 		cd alt-split &&
+		rm -f .git/objects/info/commit-graph &&
 		echo "$(pwd)"/../.git/objects >.git/objects/info/alternates &&
 		test_commit 18 &&
 		git commit-graph write --reachable --split &&
diff --git a/t/t6011-rev-list-with-bad-commit.sh b/t/t6011-rev-list-with-bad-commit.sh
index 545b461e51..bad02cf5b8 100755
--- a/t/t6011-rev-list-with-bad-commit.sh
+++ b/t/t6011-rev-list-with-bad-commit.sh
@@ -42,7 +42,7 @@ test_expect_success 'corrupt second commit object' \
    '
 
 test_expect_success 'rev-list should fail' '
-	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git rev-list --all > /dev/null
+	test_must_fail env GIT_TEST_COMMIT_GRAPH=0 git -c core.commitGraph=false rev-list --all > /dev/null
 '
 
 test_expect_success 'git repack _MUST_ fail' \

Documentation/config/feature.txt, Documentation/config/fetch.txt, Documentation/config/pack.txt, fetch-negotiator.c, fetch-negotiator.h, fetch-pack.c, repo-settings.c, repository.h, t/t5552-skipping-fetch-negotiator.sh

diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index 8ea198a642..545522f306 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -4,6 +4,20 @@ feature.*::
 	developer community as recommended defaults and are subject to change.
 	In particular, new config options may be added with different defaults.
 
+feature.experimental::
+	Enable config options that are new to Git, and are being considered for
+	future defaults. Config settings included here may be added or removed
+	with each release, including minor version updates. These settings may
+	have unintended interactions since they are so new. Please enable this
+	setting if you are interested in providing feedback on experimental
+	features. The new default values are:
++
+* `pack.useSparse=true` uses a new algorithm when constructing a pack-file
+which can improve `git push` performance in repos with many files.
++
+* `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
+skipping more commits at a time, reducing the number of round trips.
+
 feature.manyFiles::
 	Enable config options that optimize for repos with many files in the
 	working directory. With many files, commands such as `git status` and
diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
index ba890b5884..d402110638 100644
--- a/Documentation/config/fetch.txt
+++ b/Documentation/config/fetch.txt
@@ -59,7 +59,8 @@ fetch.negotiationAlgorithm::
 	effort to converge faster, but may result in a larger-than-necessary
 	packfile; The default is "default" which instructs Git to use the default algorithm
 	that never skips commits (unless the server has acknowledged it or one
-	of its descendants).
+	of its descendants). If `feature.experimental` is enabled, then this
+	setting defaults to "skipping".
 	Unknown values will cause 'git fetch' to error out.
 +
 See also the `--negotiation-tip` option for linkgit:git-fetch[1].
diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index 9cdcfa7324..1d66f0c992 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -112,7 +112,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames.
+	commits contain certain types of direct renames. Default is `false`
+	unless `feature.experimental` is enabled.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.
diff --git a/fetch-negotiator.c b/fetch-negotiator.c
index d6d685cba0..0a1357dc9d 100644
--- a/fetch-negotiator.c
+++ b/fetch-negotiator.c
@@ -2,19 +2,20 @@
 #include "fetch-negotiator.h"
 #include "negotiator/default.h"
 #include "negotiator/skipping.h"
+#include "repository.h"
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm)
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator)
 {
-	if (algorithm) {
-		if (!strcmp(algorithm, "skipping")) {
-			skipping_negotiator_init(negotiator);
-			return;
-		} else if (!strcmp(algorithm, "default")) {
-			/* Fall through to default initialization */
-		} else {
-			die("unknown fetch negotiation algorithm '%s'", algorithm);
-		}
+	prepare_repo_settings(r);
+	switch(r->settings.fetch_negotiation_algorithm) {
+	case FETCH_NEGOTIATION_SKIPPING:
+		skipping_negotiator_init(negotiator);
+		return;
+
+	case FETCH_NEGOTIATION_DEFAULT:
+	default:
+		default_negotiator_init(negotiator);
+		return;
 	}
-	default_negotiator_init(negotiator);
 }
diff --git a/fetch-negotiator.h b/fetch-negotiator.h
index 9e3967ce66..ea78868504 100644
--- a/fetch-negotiator.h
+++ b/fetch-negotiator.h
@@ -2,6 +2,7 @@
 #define FETCH_NEGOTIATOR_H
 
 struct commit;
+struct repository;
 
 /*
  * An object that supplies the information needed to negotiate the contents of
@@ -52,7 +53,7 @@ struct fetch_negotiator {
 	void *data;
 };
 
-void fetch_negotiator_init(struct fetch_negotiator *negotiator,
-			   const char *algorithm);
+void fetch_negotiator_init(struct repository *r,
+			   struct fetch_negotiator *negotiator);
 
 #endif
diff --git a/fetch-pack.c b/fetch-pack.c
index 65be043f2a..d81f47c07b 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -36,7 +36,6 @@ static int agent_supported;
 static int server_supports_filtering;
 static struct lock_file shallow_lock;
 static const char *alternate_shallow_file;
-static char *negotiation_algorithm;
 static struct strbuf fsck_msg_types = STRBUF_INIT;
 
 /* Remember to update object flag allocation in object.h */
@@ -892,12 +891,13 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 				 struct shallow_info *si,
 				 char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	struct object_id oid;
 	const char *agent_feature;
 	int agent_len;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 
 	sort_ref_list(&ref, ref_compare_name);
 	QSORT(sought, nr_sought, cmp_ref_by_name);
@@ -911,7 +911,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 
 	if (server_supports("shallow"))
 		print_verbose(args, _("Server supports %s"), "shallow");
-	else if (args->depth > 0 || is_repository_shallow(the_repository))
+	else if (args->depth > 0 || is_repository_shallow(r))
 		die(_("Server does not support shallow clients"));
 	if (args->depth > 0 || args->deepen_since || args->deepen_not)
 		args->deepen = 1;
@@ -1379,6 +1379,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				    struct shallow_info *si,
 				    char **pack_lockfile)
 {
+	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
 	enum fetch_state state = FETCH_CHECK_LOCAL;
 	struct oidset common = OIDSET_INIT;
@@ -1386,7 +1387,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	int in_vain = 0;
 	int haves_to_send = INITIAL_FLUSH;
 	struct fetch_negotiator negotiator;
-	fetch_negotiator_init(&negotiator, negotiation_algorithm);
+	fetch_negotiator_init(r, &negotiator);
 	packet_reader_init(&reader, fd[0], NULL, 0,
 			   PACKET_READ_CHOMP_NEWLINE |
 			   PACKET_READ_DIE_ON_ERR_PACKET);
@@ -1505,8 +1506,6 @@ static void fetch_pack_config(void)
 	git_config_get_bool("repack.usedeltabaseoffset", &prefer_ofs_delta);
 	git_config_get_bool("fetch.fsckobjects", &fetch_fsck_objects);
 	git_config_get_bool("transfer.fsckobjects", &transfer_fsck_objects);
-	git_config_get_string("fetch.negotiationalgorithm",
-			      &negotiation_algorithm);
 
 	git_config(fetch_pack_config_cb, NULL);
 }
diff --git a/repo-settings.c b/repo-settings.c
index d5bf9069f4..3779b85c17 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -36,16 +36,29 @@ void prepare_repo_settings(struct repository *r)
 		free(strval);
 	}
 
+	if (!repo_config_get_string(r, "fetch.negotiationalgorithm", &strval)) {
+		if (!strcasecmp(strval, "skipping"))
+			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
+		else
+			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_DEFAULT;
+	}
+
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
 	}
+	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
+		UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
+		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
+	}
 
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
 		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;
 	else
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_KEEP);
+
+	UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_DEFAULT);
 }
diff --git a/repository.h b/repository.h
index cf7ff0778c..4da275e73f 100644
--- a/repository.h
+++ b/repository.h
@@ -18,6 +18,13 @@ enum untracked_cache_setting {
 	UNTRACKED_CACHE_WRITE = 2
 };
 
+enum fetch_negotiation_setting {
+	FETCH_NEGOTIATION_UNSET = -1,
+	FETCH_NEGOTIATION_NONE = 0,
+	FETCH_NEGOTIATION_DEFAULT = 1,
+	FETCH_NEGOTIATION_SKIPPING = 2,
+};
+
 struct repo_settings {
 	int initialized;
 
@@ -28,6 +35,7 @@ struct repo_settings {
 	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
+	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 };
 
 struct repository {
diff --git a/t/t5552-skipping-fetch-negotiator.sh b/t/t5552-skipping-fetch-negotiator.sh
index 8a14be51a1..f70cbcc9ca 100755
--- a/t/t5552-skipping-fetch-negotiator.sh
+++ b/t/t5552-skipping-fetch-negotiator.sh
@@ -60,29 +60,6 @@ test_expect_success 'commits with no parents are sent regardless of skip distanc
 	have_not_sent c6 c4 c3
 '
 
-test_expect_success 'unknown fetch.negotiationAlgorithm values error out' '
-	rm -rf server client trace &&
-	git init server &&
-	test_commit -C server to_fetch &&
-
-	git init client &&
-	test_commit -C client on_client &&
-	git -C client checkout on_client &&
-
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	test_must_fail git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep "unknown fetch negotiation algorithm" err &&
-
-	# Explicit "default" value
-	test_config -C client fetch.negotiationAlgorithm default &&
-	git -C client -c fetch.negotiationAlgorithm=default fetch "$(pwd)/server" &&
-
-	# Implementation detail: If there is nothing to fetch, we will not error out
-	test_config -C client fetch.negotiationAlgorithm invalid &&
-	git -C client fetch "$(pwd)/server" 2>err &&
-	test_i18ngrep ! "unknown fetch negotiation algorithm" err
-'
-
 test_expect_success 'when two skips collide, favor the larger one' '
 	rm -rf server client trace &&
 	git init server &&