Changes since v1
- use kerndoc
- be more specific about mem_cgroup_move_parent possible failures

Signed-off-by: Michal Hocko <redacted>
Reviewed-by: Tejun Heo <tj@kernel.org>

Reviewed-by: Glauber Costa <redacted>

+ * move charges to its parent or the root cgroup if the group has no
+ * parent (aka use_hierarchy==0).
+ * Although this might fail (get_page_unless_zero, isolate_lru_page or
+ * mem_cgroup_move_account fails) the failure is always temporary and
+ * it signals a race with a page removal/uncharge or migration. In the
+ * first case the page is on the way out and it will vanish from the LRU
+ * on the next attempt and the call should be retried later.
+ * Isolation from the LRU fails only if page has been isolated from
+ * the LRU since we looked at it and that usually means either global
+ * reclaim or migration going on. The page will either get back to the
+ * LRU or vanish.

I just wonder for how long can it go in the worst case?

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