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Message-ID: <6599ad830809050903s7e1a1004i6b31660502c0dcf2@mail.gmail.com>
Date: Fri, 5 Sep 2008 09:03:49 -0700
From: "Paul Menage" <menage@google.com>
To: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH][mmotm]memcg: handle null dereference of mm->owner
Cc: "Daisuke Nishimura" <nishimura@mxp.nes.nec.co.jp>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Balbir Singh" <balbir@linux.vnet.ibm.com>,
       "Hugh Dickins" <hugh@veritas.com>, "Li Zefan" <lizf@cn.fujitsu.com>,
       linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Fri, Sep 5, 2008 at 1:40 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.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