diff options
author | Tejun Heo <tj@kernel.org> | 2017-02-23 00:41:14 +0100 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-02-23 01:41:27 +0100 |
commit | 657dc2f9722092e951de95a8109428994541440b (patch) | |
tree | 9fe9284f29a067117b0c2c91b5d51602694557cd /mm/slab_common.c | |
parent | slub: separate out sysfs_slab_release() from sysfs_slab_remove() (diff) | |
download | linux-657dc2f9722092e951de95a8109428994541440b.tar.xz linux-657dc2f9722092e951de95a8109428994541440b.zip |
slab: remove synchronous rcu_barrier() call in memcg cache release path
With kmem cgroup support enabled, kmem_caches can be created and
destroyed frequently and a great number of near empty kmem_caches can
accumulate if there are a lot of transient cgroups and the system is not
under memory pressure. When memory reclaim starts under such
conditions, it can lead to consecutive deactivation and destruction of
many kmem_caches, easily hundreds of thousands on moderately large
systems, exposing scalability issues in the current slab management
code. This is one of the patches to address the issue.
SLAB_DESTORY_BY_RCU caches need to flush all RCU operations before
destruction because slab pages are freed through RCU and they need to be
able to dereference the associated kmem_cache. Currently, it's done
synchronously with rcu_barrier(). As rcu_barrier() is expensive
time-wise, slab implements a batching mechanism so that rcu_barrier()
can be done for multiple caches at the same time.
Unfortunately, the rcu_barrier() is in synchronous path which is called
while holding cgroup_mutex and the batching is too limited to be
actually helpful.
This patch updates the cache release path so that the batching is
asynchronous and global. All SLAB_DESTORY_BY_RCU caches are queued
globally and a work item consumes the list. The work item calls
rcu_barrier() only once for all caches that are currently queued.
* release_caches() is removed and shutdown_cache() now either directly
release the cache or schedules a RCU callback to do that. This
makes the cache inaccessible once shutdown_cache() is called and
makes it impossible for shutdown_memcg_caches() to do memcg-specific
cleanups afterwards. Move memcg-specific part into a helper,
unlink_memcg_cache(), and make shutdown_cache() call it directly.
Link: http://lkml.kernel.org/r/20170117235411.9408-4-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jay Vana <jsvana@fb.com>
Acked-by: Vladimir Davydov <vdavydov@tarantool.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab_common.c')
-rw-r--r-- | mm/slab_common.c | 102 |
1 files changed, 60 insertions, 42 deletions
diff --git a/mm/slab_common.c b/mm/slab_common.c index e6311b2dbba6..ac469c815587 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -30,6 +30,11 @@ LIST_HEAD(slab_caches); DEFINE_MUTEX(slab_mutex); struct kmem_cache *kmem_cache; +static LIST_HEAD(slab_caches_to_rcu_destroy); +static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work); +static DECLARE_WORK(slab_caches_to_rcu_destroy_work, + slab_caches_to_rcu_destroy_workfn); + /* * Set of flags that will prevent slab merging */ @@ -215,6 +220,11 @@ int memcg_update_all_caches(int num_memcgs) mutex_unlock(&slab_mutex); return ret; } + +static void unlink_memcg_cache(struct kmem_cache *s) +{ + list_del(&s->memcg_params.list); +} #else static inline int init_memcg_params(struct kmem_cache *s, struct mem_cgroup *memcg, struct kmem_cache *root_cache) @@ -225,6 +235,10 @@ static inline int init_memcg_params(struct kmem_cache *s, static inline void destroy_memcg_params(struct kmem_cache *s) { } + +static inline void unlink_memcg_cache(struct kmem_cache *s) +{ +} #endif /* CONFIG_MEMCG && !CONFIG_SLOB */ /* @@ -461,33 +475,59 @@ out_unlock: } EXPORT_SYMBOL(kmem_cache_create); -static int shutdown_cache(struct kmem_cache *s, - struct list_head *release, bool *need_rcu_barrier) +static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) { - if (__kmem_cache_shutdown(s) != 0) - return -EBUSY; + LIST_HEAD(to_destroy); + struct kmem_cache *s, *s2; - if (s->flags & SLAB_DESTROY_BY_RCU) - *need_rcu_barrier = true; + /* + * On destruction, SLAB_DESTROY_BY_RCU kmem_caches are put on the + * @slab_caches_to_rcu_destroy list. The slab pages are freed + * through RCU and and the associated kmem_cache are dereferenced + * while freeing the pages, so the kmem_caches should be freed only + * after the pending RCU operations are finished. As rcu_barrier() + * is a pretty slow operation, we batch all pending destructions + * asynchronously. + */ + mutex_lock(&slab_mutex); + list_splice_init(&slab_caches_to_rcu_destroy, &to_destroy); + mutex_unlock(&slab_mutex); - list_move(&s->list, release); - return 0; + if (list_empty(&to_destroy)) + return; + + rcu_barrier(); + + list_for_each_entry_safe(s, s2, &to_destroy, list) { +#ifdef SLAB_SUPPORTS_SYSFS + sysfs_slab_release(s); +#else + slab_kmem_cache_release(s); +#endif + } } -static void release_caches(struct list_head *release, bool need_rcu_barrier) +static int shutdown_cache(struct kmem_cache *s) { - struct kmem_cache *s, *s2; + if (__kmem_cache_shutdown(s) != 0) + return -EBUSY; - if (need_rcu_barrier) - rcu_barrier(); + list_del(&s->list); + if (!is_root_cache(s)) + unlink_memcg_cache(s); - list_for_each_entry_safe(s, s2, release, list) { + if (s->flags & SLAB_DESTROY_BY_RCU) { + list_add_tail(&s->list, &slab_caches_to_rcu_destroy); + schedule_work(&slab_caches_to_rcu_destroy_work); + } else { #ifdef SLAB_SUPPORTS_SYSFS sysfs_slab_release(s); #else slab_kmem_cache_release(s); #endif } + + return 0; } #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB) @@ -602,22 +642,8 @@ void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg) put_online_cpus(); } -static int __shutdown_memcg_cache(struct kmem_cache *s, - struct list_head *release, bool *need_rcu_barrier) -{ - BUG_ON(is_root_cache(s)); - - if (shutdown_cache(s, release, need_rcu_barrier)) - return -EBUSY; - - list_del(&s->memcg_params.list); - return 0; -} - void memcg_destroy_kmem_caches(struct mem_cgroup *memcg) { - LIST_HEAD(release); - bool need_rcu_barrier = false; struct kmem_cache *s, *s2; get_online_cpus(); @@ -631,18 +657,15 @@ void memcg_destroy_kmem_caches(struct mem_cgroup *memcg) * The cgroup is about to be freed and therefore has no charges * left. Hence, all its caches must be empty by now. */ - BUG_ON(__shutdown_memcg_cache(s, &release, &need_rcu_barrier)); + BUG_ON(shutdown_cache(s)); } mutex_unlock(&slab_mutex); put_online_mems(); put_online_cpus(); - - release_caches(&release, need_rcu_barrier); } -static int shutdown_memcg_caches(struct kmem_cache *s, - struct list_head *release, bool *need_rcu_barrier) +static int shutdown_memcg_caches(struct kmem_cache *s) { struct memcg_cache_array *arr; struct kmem_cache *c, *c2; @@ -661,7 +684,7 @@ static int shutdown_memcg_caches(struct kmem_cache *s, c = arr->entries[i]; if (!c) continue; - if (__shutdown_memcg_cache(c, release, need_rcu_barrier)) + if (shutdown_cache(c)) /* * The cache still has objects. Move it to a temporary * list so as not to try to destroy it for a second @@ -684,7 +707,7 @@ static int shutdown_memcg_caches(struct kmem_cache *s, */ list_for_each_entry_safe(c, c2, &s->memcg_params.list, memcg_params.list) - __shutdown_memcg_cache(c, release, need_rcu_barrier); + shutdown_cache(c); list_splice(&busy, &s->memcg_params.list); @@ -697,8 +720,7 @@ static int shutdown_memcg_caches(struct kmem_cache *s, return 0; } #else -static inline int shutdown_memcg_caches(struct kmem_cache *s, - struct list_head *release, bool *need_rcu_barrier) +static inline int shutdown_memcg_caches(struct kmem_cache *s) { return 0; } @@ -714,8 +736,6 @@ void slab_kmem_cache_release(struct kmem_cache *s) void kmem_cache_destroy(struct kmem_cache *s) { - LIST_HEAD(release); - bool need_rcu_barrier = false; int err; if (unlikely(!s)) @@ -731,9 +751,9 @@ void kmem_cache_destroy(struct kmem_cache *s) if (s->refcount) goto out_unlock; - err = shutdown_memcg_caches(s, &release, &need_rcu_barrier); + err = shutdown_memcg_caches(s); if (!err) - err = shutdown_cache(s, &release, &need_rcu_barrier); + err = shutdown_cache(s); if (err) { pr_err("kmem_cache_destroy %s: Slab cache still has objects\n", @@ -745,8 +765,6 @@ out_unlock: put_online_mems(); put_online_cpus(); - - release_caches(&release, need_rcu_barrier); } EXPORT_SYMBOL(kmem_cache_destroy); |