gc: add --keep-largest-pack option

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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 25 insertions, 0 deletions

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 &&