[PATCH RFC 5/5] backfill: report total size of missing blobs in --dry-run

From

Pablo Sabater <pabloosabaterr@gmail.com>

Date

Sep 30, 2026, 00:21 UTC

Message-ID

<20260930-backfill-dryrun-v1-5-1128f247ee01@gmail.com>

In-Reply-To

<20260930-backfill-dryrun-v1-0-1128f247ee01@gmail.com>

Signed-off-by: Pablo Sabater <pabloosabaterr@gmail.com>
---
 Documentation/git-backfill.adoc |  6 +++-
 builtin/backfill.c              | 70 ++++++++++++++++++++++++++++++++++++++---
 t/t5620-backfill.sh             | 22 +++++++++++++
 3 files changed, 92 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-backfill.adoc b/Documentation/git-backfill.adoc
index 08f19fea17..660e1c17c0 100644
--- a/Documentation/git-backfill.adoc
+++ b/Documentation/git-backfill.adoc
@@ -72,7 +72,11 @@ OPTIONS
 
 `--dry-run`::
 	Do not download any objects. Instead, print the number of
-	missing blobs that would be downloaded.
+	missing blobs that would be downloaded and, if the promisor
+	remote supports the `object-info` capability, their total
+	size. This is the sum of the uncompressed sizes of the blobs,
+	so the space used on disk after a real backfill is usually
+	smaller.
 
 `<revision-range>`::
 	Backfill only blobs reachable from commits in the specified
diff --git a/builtin/backfill.c b/builtin/backfill.c
index 6019112966..caf1a64e95 100644
--- a/builtin/backfill.c
+++ b/builtin/backfill.c
@@ -24,6 +24,9 @@
 #include "progress.h"
 #include "packfile.h"
 #include "path-walk.h"
+#include "transport.h"
+#include "remote.h"
+#include "fetch-object-info.h"
 
 static const char * const builtin_backfill_usage[] = {
 	N_("git backfill [--min-batch-size=<n>] [--[no-]sparse] [--[no-]include-edges] [--dry-run] [<revision-range>]"),
@@ -37,7 +40,11 @@ struct backfill_context {
 	int sparse;
 	int include_edges;
 	int dry_run;
+	int object_info_enabled;
+	size_t total_batch_size;
 	size_t total_batch_nr;
+	struct transport *object_info_transport;
+	struct fetch_object_info_results object_info_results;
 	struct rev_info revs;
 };
 
@@ -62,10 +69,47 @@ static void download_batch(struct backfill_context *ctx)
 
 static void dry_run_batch(struct backfill_context *ctx)
 {
+	struct fetch_object_info_results *results = &ctx->object_info_results;
+	enum fetch_object_info_status status;
+
 	if (!ctx->current_batch.nr)
 		return;
 
 	ctx->total_batch_nr += ctx->current_batch.nr;
+
+	if (!ctx->object_info_enabled)
+		goto cleanup;
+
+	if (!ctx->object_info_transport) {
+		struct promisor_remote *promise =
+			repo_promisor_remote_find(ctx->repo, NULL);
+		struct remote *remote = NULL;
+
+		if (!promise || !(remote = remote_get(promise->name)))
+			die(_("--dry-run requires a promisor remote"));
+
+		ctx->object_info_transport = transport_get(remote, NULL);
+
+		if (!ctx->object_info_transport->smart_options)
+			die(_("failed to get object info: smart options required"));
+	}
+
+	results->wants_size = 1;
+	status = transport_fetch_object_info(ctx->object_info_transport,
+					     &ctx->current_batch,
+					     results);
+
+	if (status == FETCH_OBJECT_INFO_NOT_ENABLED ||
+	    !results->sizes) {
+		ctx->object_info_enabled = 0;
+		goto cleanup;
+	}
+
+	for (size_t i = 0; i < results->nr; i++)
+		ctx->total_batch_size += results->sizes[i];
+
+cleanup:
+	free_fetch_object_info_results(&ctx->object_info_results);
 	oid_array_clear(&ctx->current_batch);
 }
 
@@ -157,12 +201,25 @@ static int do_backfill(struct backfill_context *ctx)
 
 	dry_run_batch(ctx);
 
-	printf(Q_("After backfill, %" PRIuMAX " blob would be fetched.\n",
-		  "After backfill, %" PRIuMAX " blobs would be fetched.\n",
-		  (unsigned long)ctx->total_batch_nr),
-	       (uintmax_t)ctx->total_batch_nr);
+	if (ctx->object_info_enabled && ctx->total_batch_nr) {
+		struct strbuf size = STRBUF_INIT;
+
+		strbuf_humanise_bytes(&size, ctx->total_batch_size);
+		printf(Q_("After backfill, %" PRIuMAX " blob would be fetched (%s).\n",
+			  "After backfill, %" PRIuMAX " blobs would be fetched (%s).\n",
+			  (unsigned long)ctx->total_batch_nr),
+		       (uintmax_t)ctx->total_batch_nr, size.buf);
+		strbuf_release(&size);
+	} else {
+		printf(Q_("After backfill, %" PRIuMAX " blob would be fetched.\n",
+			  "After backfill, %" PRIuMAX " blobs would be fetched.\n",
+			  (unsigned long)ctx->total_batch_nr),
+		       (uintmax_t)ctx->total_batch_nr);
+	}
 
 end:
+	if (ctx->object_info_transport)
+		transport_disconnect(ctx->object_info_transport);
 	path_walk_info_clear(&info);
 	return ret;
 }
@@ -177,6 +234,8 @@ int cmd_backfill(int argc, const char **argv, const char *prefix, struct reposit
 		.sparse = -1,
 		.revs = REV_INFO_INIT,
 		.include_edges = 1,
+		.object_info_results = FETCH_OBJECT_INFO_RESULTS_INIT,
+		.object_info_enabled = 1,
 	};
 	struct option options[] = {
 		OPT_UNSIGNED(0, "min-batch-size", &ctx.min_batch_size,
@@ -185,7 +244,8 @@ int cmd_backfill(int argc, const char **argv, const char *prefix, struct reposit
 			 N_("Restrict the missing objects to the current sparse-checkout")),
 		OPT_BOOL(0, "include-edges", &ctx.include_edges,
 			 N_("Include blobs from boundary commits in the backfill")),
-		OPT__DRY_RUN(&ctx.dry_run, N_("Preview the number of blobs to be fetched")),
+		OPT__DRY_RUN(&ctx.dry_run, N_("Preview the number of blobs and their total "
+					      "size to be fetched")),
 		OPT_END(),
 	};
 	struct repo_config_values *cfg = repo_config_values(the_repository);
diff --git a/t/t5620-backfill.sh b/t/t5620-backfill.sh
index e76fa6081b..b21feb625c 100755
--- a/t/t5620-backfill.sh
+++ b/t/t5620-backfill.sh
@@ -167,6 +167,28 @@ test_expect_success '--dry-run with no missing blobs' '
 	test_grep "0 blobs would be fetched" out
 '
 
+test_expect_success '--dry-run reports total size with object-info' '
+	test_config -C srv.bare transfer.advertiseobjectinfo true &&
+	test_when_finished rm -rf backfill-dry-run &&
+	git clone --no-checkout --filter=blob:none \
+		--single-branch --branch=main \
+		"file://$(pwd)/srv.bare" backfill-dry-run &&
+
+	git -C backfill-dry-run backfill --dry-run >out &&
+	test_grep "48 blobs would be fetched (.*)" out
+'
+
+test_expect_success '--dry-run reports only the count without object-info' '
+	test_config -C srv.bare transfer.advertiseobjectinfo false &&
+	test_when_finished rm -rf backfill-dry-run &&
+	git clone --no-checkout --filter=blob:none \
+		--single-branch --branch=main \
+		"file://$(pwd)/srv.bare" backfill-dry-run &&
+
+	git -C backfill-dry-run backfill --dry-run >out &&
+	test_grep "48 blobs would be fetched\.$" out
+'
+
 test_expect_success 'backfill --sparse without sparse-checkout fails' '
 	git init not-sparse &&
 	test_must_fail git -C not-sparse backfill --sparse 2>err &&

-- 
2.54.0