linux-kernel - Re: [PATCH v3 2/7] socket: initial cgroup code.

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Date:	Wed, 21 Sep 2011 23:00:18 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, paul@...lmenage.org,
	lizf@...fujitsu.com, kamezawa.hiroyu@...fujitsu.com,
	ebiederm@...ssion.com, davem@...emloft.net, netdev@...r.kernel.org,
	linux-mm@...ck.org, kirill@...temov.name
Subject: Re: [PATCH v3 2/7] socket: initial cgroup code.

On Wed, Sep 21, 2011 at 11:59 AM, Glauber Costa <glommer@...allels.com> wrote:
> Right now I am working under the assumption that tasks are long lived inside
> the cgroup. Migration potentially introduces some nasty locking problems in
> the mem_schedule path.
>
> Also, unless I am missing something, the memcg already has the policy of
> not carrying charges around, probably because of this very same complexity.
>
> True that at least it won't EBUSY you... But I think this is at least a way
> to guarantee that the cgroup under our nose won't disappear in the middle of
> our allocations.

Here's the memcg user page behavior using the same pattern:

1. user page P is allocate by task T in memcg M1
2. T is moved to memcg M2.  The P charge is left behind still charged
to M1 if memory.move_charge_at_immigrate=0; or the charge is moved to
M2 if memory.move_charge_at_immigrate=1.
3. rmdir M1 will try to reclaim P (if P was left in M1).  If unable to
reclaim, then P is recharged to parent(M1).
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