mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages

Every slab page charged to a non-root memory cgroup has a pointer to the
memory cgroup and holds a reference to it, which protects a non-empty
memory cgroup from being released.  At the same time the page has a
pointer to the corresponding kmem_cache, and also hold a reference to the
kmem_cache.  And kmem_cache by itself holds a reference to the cgroup.

So there is clearly some redundancy, which allows to stop setting the
page->mem_cgroup pointer and rely on getting memcg pointer indirectly via
kmem_cache.  Further it will allow to change this pointer easier, without
a need to go over all charged pages.

So let's stop setting page->mem_cgroup pointer for slab pages, and stop
using the css refcounter directly for protecting the memory cgroup from
going away.  Instead rely on kmem_cache as an intermediate object.

Make sure that vmstats and shrinker lists are working as previously, as
well as /proc/kpagecgroup interface.

Link: http://lkml.kernel.org/r/20190611231813.3148843-10-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 927d85be32f6..0f1f6b06b7f3 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/mutex.h>
 #include <linux/memcontrol.h>
+#include "slab.h"
 
 #ifdef CONFIG_MEMCG_KMEM
 static LIST_HEAD(list_lrus);
@@ -63,7 +64,7 @@ static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
 	if (!memcg_kmem_enabled())
 		return NULL;
 	page = virt_to_head_page(ptr);
-	return page->mem_cgroup;
+	return memcg_from_slab_page(page);
 }
 
 static inline struct list_lru_one *