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authorTejun Heo <tj@kernel.org>2017-02-22 15:41:30 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-22 16:41:27 -0800
commit01fb58bcba63f8fba37581c24c99e9a515dd0335 (patch)
tree475ebac1b656204783280c52acf315dfd3caea03 /mm
parentc9fc586403e7c85eee06b2d5dea14ce71c00fcd8 (diff)
slab: remove synchronous synchronize_sched() from memcg cache deactivation 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. slub uses synchronize_sched() to deactivate a memcg cache. synchronize_sched() is an expensive and slow operation and doesn't scale when a huge number of caches are destroyed back-to-back. While there used to be a simple batching mechanism, the batching was too restricted to be helpful. This patch implements slab_deactivate_memcg_cache_rcu_sched() which slub can use to schedule sched RCU callback instead of performing synchronize_sched() synchronously while holding cgroup_mutex. While this adds online cpus, mems and slab_mutex operations, operating on these locks back-to-back from the same kworker, which is what's gonna happen when there are many to deactivate, isn't expensive at all and this gets rid of the scalability problem completely. Link: http://lkml.kernel.org/r/20170117235411.9408-9-tj@kernel.org Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Jay Vana <jsvana@fb.com> Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com> 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')
-rw-r--r--mm/slab.h2
-rw-r--r--mm/slab_common.c60
-rw-r--r--mm/slub.c12
3 files changed, 70 insertions, 4 deletions
diff --git a/mm/slab.h b/mm/slab.h
index 7bff1ee513c2..65e7c3fcac72 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -307,6 +307,8 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
extern void slab_init_memcg_params(struct kmem_cache *);
extern void memcg_link_cache(struct kmem_cache *s);
+extern void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
+ void (*deact_fn)(struct kmem_cache *));
#else /* CONFIG_MEMCG && !CONFIG_SLOB */
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 59e41bb81575..c549296c7981 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -627,6 +627,66 @@ out_unlock:
put_online_cpus();
}
+static void kmemcg_deactivate_workfn(struct work_struct *work)
+{
+ struct kmem_cache *s = container_of(work, struct kmem_cache,
+ memcg_params.deact_work);
+
+ get_online_cpus();
+ get_online_mems();
+
+ mutex_lock(&slab_mutex);
+
+ s->memcg_params.deact_fn(s);
+
+ mutex_unlock(&slab_mutex);
+
+ put_online_mems();
+ put_online_cpus();
+
+ /* done, put the ref from slab_deactivate_memcg_cache_rcu_sched() */
+ css_put(&s->memcg_params.memcg->css);
+}
+
+static void kmemcg_deactivate_rcufn(struct rcu_head *head)
+{
+ struct kmem_cache *s = container_of(head, struct kmem_cache,
+ memcg_params.deact_rcu_head);
+
+ /*
+ * We need to grab blocking locks. Bounce to ->deact_work. The
+ * work item shares the space with the RCU head and can't be
+ * initialized eariler.
+ */
+ INIT_WORK(&s->memcg_params.deact_work, kmemcg_deactivate_workfn);
+ schedule_work(&s->memcg_params.deact_work);
+}
+
+/**
+ * slab_deactivate_memcg_cache_rcu_sched - schedule deactivation after a
+ * sched RCU grace period
+ * @s: target kmem_cache
+ * @deact_fn: deactivation function to call
+ *
+ * Schedule @deact_fn to be invoked with online cpus, mems and slab_mutex
+ * held after a sched RCU grace period. The slab is guaranteed to stay
+ * alive until @deact_fn is finished. This is to be used from
+ * __kmemcg_cache_deactivate().
+ */
+void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
+ void (*deact_fn)(struct kmem_cache *))
+{
+ if (WARN_ON_ONCE(is_root_cache(s)) ||
+ WARN_ON_ONCE(s->memcg_params.deact_fn))
+ return;
+
+ /* pin memcg so that @s doesn't get destroyed in the middle */
+ css_get(&s->memcg_params.memcg->css);
+
+ s->memcg_params.deact_fn = deact_fn;
+ call_rcu_sched(&s->memcg_params.deact_rcu_head, kmemcg_deactivate_rcufn);
+}
+
void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
{
int idx;
diff --git a/mm/slub.c b/mm/slub.c
index 8a4591526f37..62d0b557a596 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3957,6 +3957,12 @@ int __kmem_cache_shrink(struct kmem_cache *s)
}
#ifdef CONFIG_MEMCG
+static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
+{
+ /* called with all the locks held after a sched RCU grace period */
+ __kmem_cache_shrink(s);
+}
+
void __kmemcg_cache_deactivate(struct kmem_cache *s)
{
/*
@@ -3968,11 +3974,9 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
/*
* s->cpu_partial is checked locklessly (see put_cpu_partial), so
- * we have to make sure the change is visible.
+ * we have to make sure the change is visible before shrinking.
*/
- synchronize_sched();
-
- __kmem_cache_shrink(s);
+ slab_deactivate_memcg_cache_rcu_sched(s, kmemcg_cache_deact_after_rcu);
}
#endif