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[PATCH 3/7] gc: add --keep-largest-pack option

From
Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Date
Apr 14, 2018, 15:26 UTC
Message-ID
<20180414152642.4666-4-pclouds@gmail.com>
In-Reply-To
<20180414152642.4666-1-pclouds@gmail.com>

This adds a new repack mode that combines everything into a secondary pack, leaving the largest pack alone.

This could help reduce memory pressure. On linux-2.6.git, valgrind massif reports 1.6GB heap in "pack all" case, and 535MB in "pack all except the base pack" case. We save roughly 1GB memory by excluding the base pack.

This should also lower I/O because we don't have to rewrite a giant pack every time (e.g. for linux-2.6.git that's a 1.4GB pack file)..

PS. The use of string_list here seems overkill, but we'll need it in the next patch...

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-gc.txt |  6 +++++-
 builtin/gc.c             | 45 ++++++++++++++++++++++++++++++++++++----
 t/t6500-gc.sh            | 25 ++++++++++++++++++++++
 3 files changed, 71 insertions(+), 5 deletions(-)
diff --git a/Documentation/git-gc.txt b/Documentation/git-gc.txt
index 3126e0dd00..8f903231da 100644
--- a/Documentation/git-gc.txt
+++ b/Documentation/git-gc.txt
@@ -9,7 +9,7 @@ git-gc - Cleanup unnecessary files and optimize the local repository
 SYNOPSIS
 --------
 [verse]
-'git gc' [--aggressive] [--auto] [--quiet] [--prune=<date> | --no-prune] [--force]
+'git gc' [--aggressive] [--auto] [--quiet] [--prune=<date> | --no-prune] [--force] [--keep-largest-pack]
 
 DESCRIPTION
 -----------
@@ -84,6 +84,10 @@ be performed as well.
 	Force `git gc` to run even if there may be another `git gc`
 	instance running on this repository.
 
+--keep-largest-pack::
+	All packs except the largest pack and those marked with a
+	`.keep` files are consolidated into a single pack.
+
 Configuration
 -------------
 
diff --git a/builtin/gc.c b/builtin/gc.c
index 3e67124eaa..f251662a8f 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -166,6 +166,22 @@ static int too_many_loose_objects(void)
 	return needed;
 }
 
+static void find_base_packs(struct string_list *packs)
+{
+	struct packed_git *p, *base = NULL;
+
+	for (p = get_packed_git(the_repository); p; p = p->next) {
+		if (!p->pack_local)
+			continue;
+		if (!base || base->pack_size < p->pack_size) {
+			base = p;
+		}
+	}
+
+	if (base)
+		string_list_append(packs, base->pack_name);
+}
+
 static int too_many_packs(void)
 {
 	struct packed_git *p;
@@ -188,7 +204,13 @@ static int too_many_packs(void)
 	return gc_auto_pack_limit < cnt;
 }
 
-static void add_repack_all_option(void)
+static int keep_one_pack(struct string_list_item *item, void *data)
+{
+	argv_array_pushf(&repack, "--keep-pack=%s", basename(item->string));
+	return 0;
+}
+
+static void add_repack_all_option(struct string_list *keep_pack)
 {
 	if (prune_expire && !strcmp(prune_expire, "now"))
 		argv_array_push(&repack, "-a");
@@ -197,6 +219,9 @@ static void add_repack_all_option(void)
 		if (prune_expire)
 			argv_array_pushf(&repack, "--unpack-unreachable=%s", prune_expire);
 	}
+
+	if (keep_pack)
+		for_each_string_list(keep_pack, keep_one_pack, NULL);
 }
 
 static void add_repack_incremental_option(void)
@@ -220,7 +245,7 @@ static int need_to_gc(void)
 	 * there is no need.
 	 */
 	if (too_many_packs())
-		add_repack_all_option();
+		add_repack_all_option(NULL);
 	else if (too_many_loose_objects())
 		add_repack_incremental_option();
 	else
@@ -354,6 +379,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	const char *name;
 	pid_t pid;
 	int daemonized = 0;
+	int keep_base_pack = -1;
 
 	struct option builtin_gc_options[] = {
 		OPT__QUIET(&quiet, N_("suppress progress reporting")),
@@ -366,6 +392,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		OPT_BOOL_F(0, "force", &force,
 			   N_("force running gc even if there may be another gc running"),
 			   PARSE_OPT_NOCOMPLETE),
+		OPT_BOOL(0, "keep-largest-pack", &keep_base_pack,
+			 N_("repack all other packs except the largest pack")),
 		OPT_END()
 	};
 
@@ -431,8 +459,17 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			 */
 			daemonized = !daemonize();
 		}
-	} else
-		add_repack_all_option();
+	} else {
+		struct string_list keep_pack = STRING_LIST_INIT_NODUP;
+
+		if (keep_base_pack != -1) {
+			if (keep_base_pack)
+				find_base_packs(&keep_pack);
+		}
+
+		add_repack_all_option(&keep_pack);
+		string_list_clear(&keep_pack, 0);
+	}
 
 	name = lock_repo_for_gc(force, &pid);
 	if (name) {
diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index d5255dd576..c42f60bc5b 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -43,6 +43,31 @@ test_expect_success 'gc is not aborted due to a stale symref' '
 	)
 '
 
+test_expect_success 'gc --keep-largest-pack' '
+	test_create_repo keep-pack &&
+	(
+		cd keep-pack &&
+		test_commit one &&
+		test_commit two &&
+		test_commit three &&
+		git gc &&
+		( cd .git/objects/pack && ls *.pack ) >pack-list &&
+		test_line_count = 1 pack-list &&
+		BASE_PACK=.git/objects/pack/pack-*.pack &&
+		test_commit four &&
+		git repack -d &&
+		test_commit five &&
+		git repack -d &&
+		( cd .git/objects/pack && ls *.pack ) >pack-list &&
+		test_line_count = 3 pack-list &&
+		git gc --keep-largest-pack &&
+		( cd .git/objects/pack && ls *.pack ) >pack-list &&
+		test_line_count = 2 pack-list &&
+		test_path_is_file $BASE_PACK &&
+		git fsck
+	)
+'
+
 test_expect_success 'auto gc with too many loose objects does not attempt to create bitmaps' '
 	test_config gc.auto 3 &&
 	test_config gc.autodetach false &&

-- 
2.17.0.367.g5dd2e386c3
Previous: Nguyễn Thái Ngọc DuyNext: Nguyễn Thái Ngọc Duy
Message 2 of 19 in “nd/repack-keep-pack update”
  1. 0/7 nd/repack-keep-pack updateNguyễn Thái Ngọc Duy, Apr 14, 2018
  2. 3/7 gc: add --keep-largest-pack optionNguyễn Thái Ngọc Duy, Apr 14, 2018
  3. 2/7 repack: add --keep-pack optionNguyễn Thái Ngọc Duy, Apr 14, 2018
  4. 7/7 pack-objects: show some progress when counting kept objectsNguyễn Thái Ngọc Duy, Apr 14, 2018
  5. 5/7 gc: handle a corner case in gc.bigPackThresholdNguyễn Thái Ngọc Duy, Apr 14, 2018
  6. 6/7 gc --auto: exclude base pack if not enough mem to "repack -ad"Nguyễn Thái Ngọc Duy, Apr 14, 2018
  7. 4/7 gc: add gc.bigPackThreshold configNguyễn Thái Ngọc Duy, Apr 14, 2018
  8. 1/7 t7700: have closing quote of a test at the beginning of lineNguyễn Thái Ngọc Duy, Apr 14, 2018
  9. Ævar Arnfjörð BjarmasonApr 14, 2018
  10. Junio C HamanoApr 14, 2018
  11. 0/7 nd/repack-keep-pack updateNguyễn Thái Ngọc Duy, Apr 15, 2018
  12. 1/7 t7700: have closing quote of a test at the beginning of lineNguyễn Thái Ngọc Duy, Apr 15, 2018
  13. 2/7 repack: add --keep-pack optionNguyễn Thái Ngọc Duy, Apr 15, 2018
  14. 5/7 gc: handle a corner case in gc.bigPackThresholdNguyễn Thái Ngọc Duy, Apr 15, 2018
  15. 7/7 pack-objects: show some progress when counting kept objectsNguyễn Thái Ngọc Duy, Apr 15, 2018
  16. 6/7 gc --auto: exclude base pack if not enough mem to "repack -ad"Nguyễn Thái Ngọc Duy, Apr 15, 2018
  17. 3/7 gc: add --keep-largest-pack optionNguyễn Thái Ngọc Duy, Apr 15, 2018
  18. 4/7 gc: add gc.bigPackThreshold configNguyễn Thái Ngọc Duy, Apr 15, 2018
  19. Junio C HamanoApr 16, 2018

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