On Fri, Sep 09, 2016 at 03:47:35PM -0700, Junio C Hamano wrote:
> * jk/delta-base-cache (2016-08-23) 7 commits
> (merged to 'next' on 2016-08-25 at f1c141a)
> + t/perf: add basic perf tests for delta base cache
> + delta_base_cache: use hashmap.h
> + delta_base_cache: drop special treatment of blobs
> + delta_base_cache: use list.h for LRU
> + release_delta_base_cache: reuse existing detach function
> + clear_delta_base_cache_entry: use a more descriptive name
> + cache_or_unpack_entry: drop keep_cache parameter
>
> The delta-base-cache mechanism has been a key to the performance in
> a repository with a tightly packed packfile, but it did not scale
> well even with a larger value of core.deltaBaseCacheLimit.
I happened to notice today that this topic needs a minor tweak:
-- >8 --
Subject: [PATCH] add_delta_base_cache: use list_for_each_safe
We may remove elements from the list while we are iterating,
which requires using a second temporary pointer. Otherwise
stepping to the next element of the list might involve
looking at freed memory (which generally works in practice,
as we _just_ freed it, but of course is wrong to rely on;
valgrind notices it).
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
sha1_file.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/sha1_file.c b/sha1_file.c
index a57b71d..132c861 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -2187,11 +2187,11 @@ static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
void *base, unsigned long base_size, enum object_type type)
{
struct delta_base_cache_entry *ent = xmalloc(sizeof(*ent));
- struct list_head *lru;
+ struct list_head *lru, *tmp;
delta_base_cached += base_size;
- list_for_each(lru, &delta_base_cache_lru) {
+ list_for_each_safe(lru, tmp, &delta_base_cache_lru) {
struct delta_base_cache_entry *f =
list_entry(lru, struct delta_base_cache_entry, lru);
if (delta_base_cached <= delta_base_cache_limit)
--
2.10.0.230.g6f8d04b