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

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.

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>
Cc: 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>