don't let the delta cache grow unbounded in 'git repack'

I have 4GB of RAM on my system which should, in theory, be quite enough
to repack a 600 MB repository.  However the unbounded delta cache size
always pushes it into swap, at which point everything virtually comes to
a halt.  So unbounded caches are never a good idea.

A default of 256MB should be a good compromize between memory usage and
speed where medium sized repositories are still likely to fit in the
cache with a reasonable memory usage, and larger repositories are going
to take quite some time to repack already anyway.

While at it, clarify the associated config variable documentation
entries a bit.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index ef4bf6b..9cc8a84 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -86,7 +86,7 @@ static int pack_compression_level = Z_DEFAULT_COMPRESSION;
 static int pack_compression_seen;
 
 static unsigned long delta_cache_size = 0;
-static unsigned long max_delta_cache_size = 0;
+static unsigned long max_delta_cache_size = 256 * 1024 * 1024;
 static unsigned long cache_max_small_delta_size = 1000;
 
 static unsigned long window_memory_limit = 0;