memcg: only check memcg_kmem_skip_account in __memcg_kmem_get_cache

__memcg_kmem_get_cache can recurse if it calls kmalloc (which it does if
the cgroup's kmem cache doesn't exist), because kmalloc may call
__memcg_kmem_get_cache internally again.  To avoid the recursion, we use
the task_struct->memcg_kmem_skip_account flag.

However, there's no need checking the flag in memcg_kmem_newpage_charge,
because there's no way how this function could result in recursion, if
called from memcg_kmem_get_cache.  So let's remove the redundant code.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bb8c237026ccd0960f52a401f7423ce1f811ae82..d9fab72da52e926797447e9726ff6bdcbca62df4 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2905,34 +2905,6 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
 
        *_memcg = NULL;
 
-       /*
-        * Disabling accounting is only relevant for some specific memcg
-        * internal allocations. Therefore we would initially not have such
-        * check here, since direct calls to the page allocator that are
-        * accounted to kmemcg (alloc_kmem_pages and friends) only happen
-        * outside memcg core. We are mostly concerned with cache allocations,
-        * and by having this test at memcg_kmem_get_cache, we are already able
-        * to relay the allocation to the root cache and bypass the memcg cache
-        * altogether.
-        *
-        * There is one exception, though: the SLUB allocator does not create
-        * large order caches, but rather service large kmallocs directly from
-        * the page allocator. Therefore, the following sequence when backed by
-        * the SLUB allocator:
-        *
-        *      memcg_stop_kmem_account();
-        *      kmalloc(<large_number>)
-        *      memcg_resume_kmem_account();
-        *
-        * would effectively ignore the fact that we should skip accounting,
-        * since it will drive us directly to this function without passing
-        * through the cache selector memcg_kmem_get_cache. Such large
-        * allocations are extremely rare but can happen, for instance, for the
-        * cache arrays. We bring this test here.
-        */
-       if (current->memcg_kmem_skip_account)
-               return true;
-
        memcg = get_mem_cgroup_from_mm(current->mm);
 
        if (!memcg_kmem_is_active(memcg)) {