[PATCH v1 0/7] memcg remove pre_destroy

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

In recent discussion, Tejun Heo, cgroup maintainer, has a plan to remove
->pre_destroy(). And now, in cgroup tree, pre_destroy() failure cause WARNING.

By pre_destroy(), rmdir of cgroup can return -EBUSY or some error.
It makes cgroup complicated and unstable. I said O.K. to remove it and
this patch is modification for memcg.

One of problem in current implementation is that memcg moves all charges to
parent in pre_destroy(). At doing so, if use_hierarchy=0, pre_destroy() may
hit parent's limit and may return -EBUSY. To fix this problem, this patch
changes behavior of rmdir() as

 - if use_hierarchy=0, all remaining charges will go to root cgroup.
 - if use_hierarchy=1, all remaining charges will go to the parent.

By this, rmdir failure will not be caused by parent's limitation. And
I think this meets meaning of use_hierarchy.

This series does
  - add above change of behavior
  - use workqueue to move all pages to parent
  - remove unnecessary codes.

I'm sorry if my reply is delayed, I'm not sure I can have enough time in
this weekend. Any comments are welcomed.

Thanks,
-Kame


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