To avoid further unneed calls of do_shrink_slab() for shrinkers, which already do not have any charged objects in a memcg, their bits have to be cleared.
This patch introduces new return value SHRINK_EMPTY, which will be used in case of there is no charged objects in shrinker. We can't use 0 instead of that, as a shrinker may return 0, when it has very small amount of objects. To prevent race with parallel list lru add, we call do_shrink_slab() once again, after the bit is cleared. So, if there is a new object, we never miss it, and the bit will be restored again. The below test shows significant performance growths after using the patchset: $echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy $mkdir /sys/fs/cgroup/memory/ct $echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes $for i in `seq 0 4000`; do mkdir /sys/fs/cgroup/memory/ct/$i; echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs; mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file; done Then 4 drop_caches: $time echo 3 > /proc/sys/vm/drop_caches Times of drop_caches: *Before (4 iterations)* 0.00user 6.80system 0:06.82elapsed 99%CPU 0.00user 4.61system 0:04.62elapsed 99%CPU 0.00user 4.61system 0:04.61elapsed 99%CPU 0.00user 4.61system 0:04.61elapsed 99%CPU *After (4 iterations)* 0.00user 0.93system 0:00.94elapsed 99%CPU 0.00user 0.00system 0:00.01elapsed 80%CPU 0.00user 0.00system 0:00.01elapsed 80%CPU 0.00user 0.00system 0:00.01elapsed 81%CPU 4.61s/0.01s = 461 times faster. Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com> --- fs/super.c | 3 +++ include/linux/shrinker.h | 1 + mm/vmscan.c | 21 ++++++++++++++++++--- mm/workingset.c | 3 +++ 4 files changed, 25 insertions(+), 3 deletions(-) diff --git a/fs/super.c b/fs/super.c index 1f3dc4eab409..788ea4e6a40b 100644 --- a/fs/super.c +++ b/fs/super.c @@ -133,6 +133,9 @@ static unsigned long super_cache_count(struct shrinker *shrink, total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc); total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc); + if (!total_objects) + return SHRINK_EMPTY; + total_objects = vfs_pressure_ratio(total_objects); return total_objects; } diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 24aeed1bc332..b23180deb928 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -34,6 +34,7 @@ struct shrink_control { }; #define SHRINK_STOP (~0UL) +#define SHRINK_EMPTY (~0UL - 1) /* * A callback you can register to apply pressure to ageable caches. * diff --git a/mm/vmscan.c b/mm/vmscan.c index e1fd16bc7a9b..1fc05e8bde04 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -387,6 +387,7 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int nr) { struct shrinkers_map *map = SHRINKERS_MAP(memcg); + smp_mb__before_atomic(); /* Pairs with mb in shrink_slab() */ set_bit(nr, map->map[nid]); } #else /* CONFIG_MEMCG && !CONFIG_SLOB */ @@ -568,8 +569,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, long scanned = 0, next_deferred; freeable = shrinker->count_objects(shrinker, shrinkctl); - if (freeable == 0) - return 0; + if (freeable == 0 || freeable == SHRINK_EMPTY) + return freeable; /* * copy the current shrinker scan count into a local variable @@ -708,6 +709,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB) if (!memcg_kmem_enabled() || memcg) { struct shrinkers_map *map; + unsigned long ret; int i; map = rcu_dereference_protected(SHRINKERS_MAP(memcg), true); @@ -724,7 +726,20 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, clear_bit(i, map->map[nid]); continue; } - freed += do_shrink_slab(&sc, shrinker, priority); + if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) + sc.nid = 0; + ret = do_shrink_slab(&sc, shrinker, priority); + if (ret == SHRINK_EMPTY) { + clear_bit(i, map->map[nid]); + /* pairs with mb in set_shrinker_bit() */ + smp_mb__after_atomic(); + ret = do_shrink_slab(&sc, shrinker, priority); + if (ret == SHRINK_EMPTY) + ret = 0; + else + set_bit(i, map->map[nid]); + } + freed += ret; if (rwsem_is_contended(&shrinker_rwsem)) { freed = freed ? : 1; diff --git a/mm/workingset.c b/mm/workingset.c index 62c9eb000c4f..dc05574f0a07 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -402,6 +402,9 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker, } max_nodes = cache >> (RADIX_TREE_MAP_SHIFT - 3); + if (!nodes) + return SHRINK_EMPTY; + if (nodes <= max_nodes) return 0; return nodes - max_nodes;