mm: memcg: count pte references from every member of the reclaimed hierarchy

The rmap walker checking page table references has historically ignored
references from VMAs that were not part of the memcg that was being
reclaimed during memcg hard limit reclaim.

When transitioning global reclaim to memcg hierarchy reclaim, I missed
that bit and now references from outside a memcg are ignored even during
global reclaim.

Reverting back to traditional behaviour - count all references during
global reclaim and only mind references of the memcg being reclaimed
during limit reclaim would be one option.

However, the more generic idea is to ignore references exactly then when
they are outside the hierarchy that is currently under reclaim; because
only then will their reclamation be of any use to help the pressure
situation.  It makes no sense to ignore references from a sibling memcg
and then evict a page that will be immediately refaulted by that sibling
which contributes to the same usage of the common ancestor under
reclaim.

The solution: make the rmap walker ignore references from VMAs that are
not part of the hierarchy that is being reclaimed.

Flat limit reclaim will stay the same, hierarchical limit reclaim will
mind the references only to pages that the hierarchy owns.  Global
reclaim, since it reclaims from all memcgs, will be fixed to regard all
references.

[akpm@linux-foundation.org: name the args in the declaration]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: Konstantin Khlebnikov<khlebnikov@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f94efd2f6c27..18ea0b7baf32 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -79,6 +79,8 @@ extern void mem_cgroup_uncharge_cache_page(struct page *page);
 
 extern void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 				     int order);
+bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
+				  struct mem_cgroup *memcg);
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg);
 
 extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
@@ -92,10 +94,13 @@ static inline
 int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
 {
 	struct mem_cgroup *memcg;
+	int match;
+
 	rcu_read_lock();
 	memcg = mem_cgroup_from_task(rcu_dereference((mm)->owner));
+	match = __mem_cgroup_same_or_subtree(cgroup, memcg);
 	rcu_read_unlock();
-	return cgroup == memcg;
+	return match;
 }
 
 extern struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg);