The patch titled
Subject: slab: remove synchronous synchronize_sched() from memcg cache deactivation path
has been added to the -mm tree. Its filename is
slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Tejun Heo <tj@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Jay Vana <jsvana@xxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/slab.h | 6 ++++
mm/slab.h | 2 +
mm/slab_common.c | 60 +++++++++++++++++++++++++++++++++++++++++
mm/slub.c | 12 +++++---
4 files changed, 76 insertions(+), 4 deletions(-)
diff -puN include/linux/slab.h~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path include/linux/slab.h
--- a/include/linux/slab.h~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path
+++ a/include/linux/slab.h
@@ -582,6 +582,12 @@ struct memcg_cache_params {
struct mem_cgroup *memcg;
struct list_head children_node;
struct list_head kmem_caches_node;
+
+ void (*deact_fn)(struct kmem_cache *);
+ union {
+ struct rcu_head deact_rcu_head;
+ struct work_struct deact_work;
+ };
};
};
};
diff -puN mm/slab.h~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path mm/slab.h
--- a/mm/slab.h~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path
+++ a/mm/slab.h
@@ -302,6 +302,8 @@ static __always_inline void memcg_unchar
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 -puN mm/slab_common.c~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path mm/slab_common.c
--- a/mm/slab_common.c~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path
+++ a/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 -puN mm/slub.c~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path mm/slub.c
--- a/mm/slub.c~slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path
+++ a/mm/slub.c
@@ -3953,6 +3953,12 @@ int __kmem_cache_shrink(struct kmem_cach
}
#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)
{
/*
@@ -3964,11 +3970,9 @@ void __kmemcg_cache_deactivate(struct km
/*
* 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
_
Patches currently in -mm which might be from tj@xxxxxxxxxx are
revert-slub-move-synchronize_sched-out-of-slab_mutex-on-shrink.patch
slub-separate-out-sysfs_slab_release-from-sysfs_slab_remove.patch
slab-remove-synchronous-rcu_barrier-call-in-memcg-cache-release-path.patch
slab-reorganize-memcg_cache_params.patch
slab-link-memcg-kmem_caches-on-their-associated-memory-cgroup.patch
slab-implement-slab_root_caches-list.patch
slab-introduce-__kmemcg_cache_deactivate.patch
slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path.patch
slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches.patch
slab-use-memcg_kmem_cache_wq-for-slab-destruction-operations.patch
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