From: Dave Chinner <dchinner@xxxxxxxxxx>
When a sudden buffer cache growth demand occurs from multiple
concurrent sources, they can all fail shaking the cache at the same
time and expand the cache. This results in the cache doubling in
size multiple times when only a single expansion was really
necessary. The resultant massive cache can cause repair to OOM as
the cache will grow to much larger than memory can actually hold.
Prevent this sudden and unnecessary expansion by rate limiting cache
growth to one size increase every tens seconds. This is sufficient
to prevent racing expansion calls from doing the wrong thing, but
not too long to prevent necesary cache growth when it is undersized.
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
include/cache.h | 1 +
libxfs/cache.c | 17 ++++++++++++++---
2 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/include/cache.h b/include/cache.h
index 552b92489e46..1b774619f7a0 100644
--- a/include/cache.h
+++ b/include/cache.h
@@ -114,6 +114,7 @@ struct cache {
unsigned long long c_misses; /* cache misses */
unsigned long long c_hits; /* cache hits */
unsigned int c_max; /* max nodes ever used */
+ time_t expand_time; /* time of last expansion */
};
struct cache *cache_init(int, unsigned int, struct cache_operations *);
diff --git a/libxfs/cache.c b/libxfs/cache.c
index 139c7c1b9e71..e10df395e60e 100644
--- a/libxfs/cache.c
+++ b/libxfs/cache.c
@@ -62,6 +62,7 @@ cache_init(
cache->bulkrelse = cache_operations->bulkrelse ?
cache_operations->bulkrelse : cache_generic_bulkrelse;
pthread_mutex_init(&cache->c_mutex, NULL);
+ time(&cache->expand_time);
for (i = 0; i < hashsize; i++) {
list_head_init(&cache->c_hash[i].ch_list);
@@ -77,15 +78,25 @@ cache_init(
return cache;
}
+/*
+ * rate limit expansion so several concurrent shakes don't instantly all
+ * expand the cache multiple times and blow repair to OOM death.
+ */
static void
cache_expand(
- struct cache * cache)
+ struct cache *cache)
{
+ time_t now;
+
pthread_mutex_lock(&cache->c_mutex);
+ time(&now);
+ if (now - cache->expand_time > 10) {
#ifdef CACHE_DEBUG
- fprintf(stderr, "doubling cache size to %d\n", 2 * cache->c_maxcount);
+ fprintf(stderr, "doubling cache size to %d\n", 2 * cache->c_maxcount);
#endif
- cache->c_maxcount *= 2;
+ cache->c_maxcount *= 2;
+ cache->expand_time = now;
+ }
pthread_mutex_unlock(&cache->c_mutex);
}
--
2.19.1
