[merged] mm-memcontrol-do-not-bypass-slab-charge-if-memcg-is-offline.patch removed from -mm tree

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The patch titled
     Subject: mm: memcontrol: do not bypass slab charge if memcg is offline
has been removed from the -mm tree.  Its filename was
     mm-memcontrol-do-not-bypass-slab-charge-if-memcg-is-offline.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Subject: mm: memcontrol: do not bypass slab charge if memcg is offline

Slab pages are charged in two steps.  First, an appropriate per memcg
cache is selected (see memcg_kmem_get_cache) basing on the current
context, then the new slab page is charged to the memory cgroup which the
selected cache was created for (see memcg_charge_slab ->
__memcg_kmem_charge_memcg).  It is OK to bypass kmemcg charge at step 1,
but if step 1 succeeded and we successfully allocated a new slab page,
step 2 must be performed, otherwise we would get a per memcg kmem cache
which contains a slab that does not hold a reference to the memory cgroup
owning the cache.  Since per memcg kmem caches are destroyed on memcg css
free, this could result in freeing a cache while there are still active
objects in it.

However, currently we will bypass slab page charge if the memory cgroup
owning the cache is offline (see __memcg_kmem_charge_memcg).  This is very
unlikely to occur in practice, because for this to happen a process must
be migrated to a different cgroup and the old cgroup must be removed while
the process is in kmalloc somewhere between steps 1 and 2 (e.g.  trying to
allocate a new page).  Nevertheless, it's still better to eliminate such a
possibility.

Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memcontrol.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff -puN mm/memcontrol.c~mm-memcontrol-do-not-bypass-slab-charge-if-memcg-is-offline mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcontrol-do-not-bypass-slab-charge-if-memcg-is-offline
+++ a/mm/memcontrol.c
@@ -2325,9 +2325,6 @@ int __memcg_kmem_charge_memcg(struct pag
 	struct page_counter *counter;
 	int ret;
 
-	if (!memcg_kmem_online(memcg))
-		return 0;
-
 	ret = try_charge(memcg, gfp, nr_pages);
 	if (ret)
 		return ret;
@@ -2346,10 +2343,11 @@ int __memcg_kmem_charge_memcg(struct pag
 int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
 {
 	struct mem_cgroup *memcg;
-	int ret;
+	int ret = 0;
 
 	memcg = get_mem_cgroup_from_mm(current->mm);
-	ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg);
+	if (memcg_kmem_online(memcg))
+		ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg);
 	css_put(&memcg->css);
 	return ret;
 }
_

Patches currently in -mm which might be from vdavydov@xxxxxxxxxxxxx are

mm-oom_reaper-implement-oom-victims-queuing-fix.patch

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