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mm: memcontrol: factor out reclaim iterator loading and updating 

mem_cgroup_iter() is too hard to follow.  Factor out the lockless reclaim
iterator loading and updating so it's easier to follow the big picture.

Also document the iterator invalidation mechanism a bit more extensively.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Glauber Costa <glommer@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
wifi-calibration
Johannes Weiner 2013-07-03 15:04:51 -07:00 committed by Linus Torvalds
parent 0f2d4a8e27
commit 519ebea3bf
1 changed files with 57 additions and 29 deletions
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86
mm/memcontrol.c
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@ -1148,6 +1148,58 @@ skip_node:
return NULL;
}
static void mem_cgroup_iter_invalidate(struct mem_cgroup *root)
{
/*
* When a group in the hierarchy below root is destroyed, the
* hierarchy iterator can no longer be trusted since it might
* have pointed to the destroyed group. Invalidate it.
*/
atomic_inc(&root->dead_count);
}
static struct mem_cgroup *
mem_cgroup_iter_load(struct mem_cgroup_reclaim_iter *iter,
struct mem_cgroup *root,
int *sequence)
{
struct mem_cgroup *position = NULL;
/*
* A cgroup destruction happens in two stages: offlining and
* release. They are separated by a RCU grace period.
*
* If the iterator is valid, we may still race with an
* offlining. The RCU lock ensures the object won't be
* released, tryget will fail if we lost the race.
*/
*sequence = atomic_read(&root->dead_count);
if (iter->last_dead_count == *sequence) {
smp_rmb();
position = iter->last_visited;
if (position && !css_tryget(&position->css))
position = NULL;
}
return position;
}
static void mem_cgroup_iter_update(struct mem_cgroup_reclaim_iter *iter,
struct mem_cgroup *last_visited,
struct mem_cgroup *new_position,
int sequence)
{
if (last_visited)
css_put(&last_visited->css);
/*
* We store the sequence count from the time @last_visited was
* loaded successfully instead of rereading it here so that we
* don't lose destruction events in between. We could have
* raced with the destruction of @new_position after all.
*/
iter->last_visited = new_position;
smp_wmb();
iter->last_dead_count = sequence;
}
/**
* mem_cgroup_iter - iterate over memory cgroup hierarchy
* @root: hierarchy root
@ -1171,7 +1223,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
{
struct mem_cgroup *memcg = NULL;
struct mem_cgroup *last_visited = NULL;
unsigned long uninitialized_var(dead_count);
if (mem_cgroup_disabled())
return NULL;
@ -1191,6 +1242,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
rcu_read_lock();
while (!memcg) {
struct mem_cgroup_reclaim_iter *uninitialized_var(iter);
int uninitialized_var(seq);
if (reclaim) {
int nid = zone_to_nid(reclaim->zone);
@ -1204,37 +1256,13 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
goto out_unlock;
}
/*
* If the dead_count mismatches, a destruction
* has happened or is happening concurrently.
* If the dead_count matches, a destruction
* might still happen concurrently, but since
* we checked under RCU, that destruction
* won't free the object until we release the
* RCU reader lock. Thus, the dead_count
* check verifies the pointer is still valid,
* css_tryget() verifies the cgroup pointed to
* is alive.
*/
dead_count = atomic_read(&root->dead_count);
if (dead_count == iter->last_dead_count) {
smp_rmb();
last_visited = iter->last_visited;
if (last_visited &&
!css_tryget(&last_visited->css))
last_visited = NULL;
}
last_visited = mem_cgroup_iter_load(iter, root, &seq);
}
memcg = __mem_cgroup_iter_next(root, last_visited);
if (reclaim) {
if (last_visited)
css_put(&last_visited->css);
iter->last_visited = memcg;
smp_wmb();
iter->last_dead_count = dead_count;
mem_cgroup_iter_update(iter, last_visited, memcg, seq);
if (!memcg)
iter->generation++;
@ -6318,14 +6346,14 @@ static void mem_cgroup_invalidate_reclaim_iterators(struct mem_cgroup *memcg)
struct mem_cgroup *parent = memcg;
while ((parent = parent_mem_cgroup(parent)))
atomic_inc(&parent->dead_count);
mem_cgroup_iter_invalidate(parent);
/*
* if the root memcg is not hierarchical we have to check it
* explicitely.
*/
if (!root_mem_cgroup->use_hierarchy)
atomic_inc(&root_mem_cgroup->dead_count);
mem_cgroup_iter_invalidate(root_mem_cgroup);
}
static void mem_cgroup_css_offline(struct cgroup *cont)