linux-kernel - Re: [PATCH][mmotm]memcg: handle null dereference of mm->owner

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Date:	Fri, 5 Sep 2008 09:03:49 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
Cc:	"Daisuke Nishimura" <nishimura@....nes.nec.co.jp>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Balbir Singh" <balbir@...ux.vnet.ibm.com>,
	"Hugh Dickins" <hugh@...itas.com>,
	"Li Zefan" <lizf@...fujitsu.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][mmotm]memcg: handle null dereference of mm->owner

On Fri, Sep 5, 2008 at 1:40 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
>
> BTW, I have a question to Balbir and Paul. (I'm sorry I missed the discussion.)
> Recently I wonder why we need MM_OWNER.
>
> - What's bad with thread's cgroup ?

Because lots of mm operations take place in a context where we don't
have a thread pointer, and hence no cgroup.

> - Why we can't disallow per-thread cgroup under memcg ?)

We can, but that's orthogonal - we still need to be able to get to
some thread (or a pointer directly in the mm to the cgroup, but with
multiple cgroup subsystems popping up that needed such a pointer, it
seems cleaner to have the owner pointer rather than adding multiple
separate cgroup subsystem pointers to mm.

Paul
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