mm: memcontrol: convert reclaim iterator to simple css refcounting
mm: memcontrol: convert reclaim iterator to simple css refcounting

The memcg reclaim iterators use a complicated weak reference scheme to
prevent pinning cgroups indefinitely in the absence of memory pressure.

However, during the ongoing cgroup core rework, css lifetime has been
decoupled such that a pinned css no longer interferes with removal of
the user-visible cgroup, and all this complexity is now unnecessary.

[829500b200af6c2a0eca4dfd5c388e6b8fbe8dc6@suse.cz: ensure that the cached reference is always released]
Signed-off-by: Johannes Weiner <331be22c6b63ca3e0a03d408c2d906b1b02cd5f2@cmpxchg.org>
Cc: Vladimir Davydov <0d62248ee021b6e01c0ee596a62a5b145b996974@parallels.com>
Cc: David Rientjes <d8cd2994e15bc61ddb2b113030bda55eebc3a0fe@google.com>
Cc: Tejun Heo <546b05909706652891a87f7bfe385ae147f61f91@kernel.org>
Signed-off-by: Michal Hocko <829500b200af6c2a0eca4dfd5c388e6b8fbe8dc6@suse.cz>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs