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Subject[PATCH 4.9 76/93] slub: move synchronize_sched out of slab_mutex on shrink
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vladimir Davydov <vdavydov.dev@gmail.com>

[ Upstream commit 89e364db71fb5e7fc8d93228152abfa67daf35fa ]

synchronize_sched() is a heavy operation and calling it per each cache
owned by a memory cgroup being destroyed may take quite some time. What
is worse, it's currently called under the slab_mutex, stalling all works
doing cache creation/destruction.

Actually, there isn't much point in calling synchronize_sched() for each
cache - it's enough to call it just once - after setting cpu_partial for
all caches and before shrinking them. This way, we can also move it out
of the slab_mutex, which we have to hold for iterating over the slab
cache list.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=172991
Link: http://lkml.kernel.org/r/0a10d71ecae3db00fb4421bcd3f82bcc911f4be4.1475329751.git.vdavydov.dev@gmail.com
Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Reported-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/slab.c | 4 ++--
mm/slab.h | 2 +-
mm/slab_common.c | 27 +++++++++++++++++++++++++--
mm/slob.c | 2 +-
mm/slub.c | 19 ++-----------------
5 files changed, 31 insertions(+), 23 deletions(-)

--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2332,7 +2332,7 @@ out:
return nr_freed;
}

-int __kmem_cache_shrink(struct kmem_cache *cachep, bool deactivate)
+int __kmem_cache_shrink(struct kmem_cache *cachep)
{
int ret = 0;
int node;
@@ -2352,7 +2352,7 @@ int __kmem_cache_shrink(struct kmem_cach

int __kmem_cache_shutdown(struct kmem_cache *cachep)
{
- return __kmem_cache_shrink(cachep, false);
+ return __kmem_cache_shrink(cachep);
}

void __kmem_cache_release(struct kmem_cache *cachep)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -146,7 +146,7 @@ static inline unsigned long kmem_cache_f

int __kmem_cache_shutdown(struct kmem_cache *);
void __kmem_cache_release(struct kmem_cache *);
-int __kmem_cache_shrink(struct kmem_cache *, bool);
+int __kmem_cache_shrink(struct kmem_cache *);
void slab_kmem_cache_release(struct kmem_cache *);

struct seq_file;
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -573,6 +573,29 @@ void memcg_deactivate_kmem_caches(struct
get_online_cpus();
get_online_mems();

+#ifdef CONFIG_SLUB
+ /*
+ * In case of SLUB, we need to disable empty slab caching to
+ * avoid pinning the offline memory cgroup by freeable kmem
+ * pages charged to it. SLAB doesn't need this, as it
+ * periodically purges unused slabs.
+ */
+ mutex_lock(&slab_mutex);
+ list_for_each_entry(s, &slab_caches, list) {
+ c = is_root_cache(s) ? cache_from_memcg_idx(s, idx) : NULL;
+ if (c) {
+ c->cpu_partial = 0;
+ c->min_partial = 0;
+ }
+ }
+ mutex_unlock(&slab_mutex);
+ /*
+ * kmem_cache->cpu_partial is checked locklessly (see
+ * put_cpu_partial()). Make sure the change is visible.
+ */
+ synchronize_sched();
+#endif
+
mutex_lock(&slab_mutex);
list_for_each_entry(s, &slab_caches, list) {
if (!is_root_cache(s))
@@ -584,7 +607,7 @@ void memcg_deactivate_kmem_caches(struct
if (!c)
continue;

- __kmem_cache_shrink(c, true);
+ __kmem_cache_shrink(c);
arr->entries[idx] = NULL;
}
mutex_unlock(&slab_mutex);
@@ -755,7 +778,7 @@ int kmem_cache_shrink(struct kmem_cache
get_online_cpus();
get_online_mems();
kasan_cache_shrink(cachep);
- ret = __kmem_cache_shrink(cachep, false);
+ ret = __kmem_cache_shrink(cachep);
put_online_mems();
put_online_cpus();
return ret;
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -634,7 +634,7 @@ void __kmem_cache_release(struct kmem_ca
{
}

-int __kmem_cache_shrink(struct kmem_cache *d, bool deactivate)
+int __kmem_cache_shrink(struct kmem_cache *d)
{
return 0;
}
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3887,7 +3887,7 @@ EXPORT_SYMBOL(kfree);
* being allocated from last increasing the chance that the last objects
* are freed in them.
*/
-int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
+int __kmem_cache_shrink(struct kmem_cache *s)
{
int node;
int i;
@@ -3899,21 +3899,6 @@ int __kmem_cache_shrink(struct kmem_cach
unsigned long flags;
int ret = 0;

- if (deactivate) {
- /*
- * Disable empty slabs caching. Used to avoid pinning offline
- * memory cgroups by kmem pages that can be freed.
- */
- s->cpu_partial = 0;
- s->min_partial = 0;
-
- /*
- * s->cpu_partial is checked locklessly (see put_cpu_partial),
- * so we have to make sure the change is visible.
- */
- synchronize_sched();
- }
-
flush_all(s);
for_each_kmem_cache_node(s, node, n) {
INIT_LIST_HEAD(&discard);
@@ -3970,7 +3955,7 @@ static int slab_mem_going_offline_callba

mutex_lock(&slab_mutex);
list_for_each_entry(s, &slab_caches, list)
- __kmem_cache_shrink(s, false);
+ __kmem_cache_shrink(s);
mutex_unlock(&slab_mutex);

return 0;

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