Re: Regression in memory consumption of git fsck

From: SZEDER Gábor <szeder.dev@gmail.com>
Date: Feb 14, 2018, 12:48 UTC
Message-ID: <20180214124828.27845-1-szeder.dev@gmail.com>
In-Reply-To: <b1a4d7ed-79b6-1f6b-1f0f-85536e943cef@gmx.de>

Show 16 quoted lines

> I've noticed that recent versions of git consume a lot of memory during
> "git fsck", to the point where I've regularly had git fall victim to
> Linux's OOM killer.
> 
> For example, if I clone torvalds/linux.git, and then run "git fsck
> --connectivity-only" in the newly cloned repository, git will consume
> more than 6GB of physical memory, while older versions peak at about 2GB.
> 
> I've managed to bisect this down to this commit in v2.14:
> 
> ad2db4030e42890e569de529e3cd61a8d03de497
> fsck: remove redundant parse_tree() invocation
> 
> If I revert that commit (on top of current master) the memory
> consumption goes down to 2GB again. The change looks relatively harmless
> to me, so does anyone know what's going on here?

I could reproduce the increased memory usage even for much smaller repositories. The patch below seems to fix it for me.

 -- >8 --

Subject: [PATCH] fsck: plug tree buffer leak

Commit ad2db4030e (fsck: remove redundant parse_tree() invocation, 2017-07-18), along with that redundant call to parse_tree() in traverse_one_object(), also removed a call to free_tree_buffer() from that function. This resulted in significantly increased memory usage of 'git fsck' because of all the non-freed tree buffers; in case of git.git and '--connectivity-only' it went from around 270MB to over 1.2GB.

Restore that free_tree_buffer() call to bring down memory usage to the previous level.

Reported-by: Dominic Sacré <dominic.sacre@gmx.de>
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---

 builtin/fsck.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 7a8a679d4f..8bc1b59daf 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -180,7 +180,10 @@ static void mark_object_reachable(struct object *obj)
 
 static int traverse_one_object(struct object *obj)
 {
-	return fsck_walk(obj, obj, &fsck_walk_options);
+	int result = fsck_walk(obj, obj, &fsck_walk_options);
+	if (obj->type == OBJ_TREE)
+		free_tree_buffer((struct tree *)obj);
+	return result;
 }
 
 static int traverse_reachable(void)

-- 
2.16.1.347.gd41f2872c6