memcg: unify slab and other kmem pages charging

We have memcg_kmem_charge and memcg_kmem_uncharge methods for charging and
uncharging kmem pages to memcg, but currently they are not used for
charging slab pages (i.e.  they are only used for charging pages allocated
with alloc_kmem_pages).  The only reason why the slab subsystem uses
special helpers, memcg_charge_slab and memcg_uncharge_slab, is that it
needs to charge to the memcg of kmem cache while memcg_charge_kmem charges
to the memcg that the current task belongs to.

To remove this diversity, this patch adds an extra argument to
__memcg_kmem_charge that can be a pointer to a memcg or NULL.  If it is
not NULL, the function tries to charge to the memcg it points to,
otherwise it charge to the current context.  Next, it makes the slab
subsystem use this function to charge slab pages.

Since memcg_charge_kmem and memcg_uncharge_kmem helpers are now used only
in __memcg_kmem_charge and __memcg_kmem_uncharge, they are inlined.  Since
__memcg_kmem_charge stores a pointer to the memcg in the page struct, we
don't need memcg_uncharge_slab anymore and can use free_kmem_pages.
Besides, one can now detect which memcg a slab page belongs to by reading
/proc/kpagecgroup.

Note, this patch switches slab to charge-after-alloc design.  Since this
design is already used for all other memcg charges, it should not make any
difference.

[hannes@cmpxchg.org: better to have an outer function than a magic parameter for the memcg lookup]
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.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>

1 files changed, 2 insertions, 4 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c952466..0ba4c86 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -752,6 +752,8 @@ static inline bool memcg_kmem_is_active(struct mem_cgroup *memcg)
  * conditions, but because they are pretty simple, they are expected to be
  * fast.
  */
+int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
+			      struct mem_cgroup *memcg);
 int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order);
 void __memcg_kmem_uncharge(struct page *page, int order);
 
@@ -770,10 +772,6 @@ void __memcg_kmem_put_cache(struct kmem_cache *cachep);
 
 struct mem_cgroup *__mem_cgroup_from_kmem(void *ptr);
 
-int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp,
-		      unsigned long nr_pages);
-void memcg_uncharge_kmem(struct mem_cgroup *memcg, unsigned long nr_pages);
-
 static inline bool __memcg_kmem_bypass(gfp_t gfp)
 {
 	if (!memcg_kmem_enabled())