linux-kernel - Re: [RFC][-mm] Memory controller add mm->owner

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Message-ID: <47EA3684.60107@linux.vnet.ibm.com>
Date:	Wed, 26 Mar 2008 17:11:56 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
CC:	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][-mm] Memory controller add mm->owner

Paul Menage wrote:
> On Wed, Mar 26, 2008 at 3:29 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>>  >>
>>  >> - in the worst case, it's not going to be worse than doing a
>>  >> for_each_thread() loop
>>  >>
>>
>>  This will have to be the common case, since you never know what combination of
>>  clone calls did CLONE_VM and what did CLONE_THREAD. At exit time, we need to pay
>>  a for_each_process() overhead.
> 
> I'm not convinced of this. All we have to do is find some other
> process p where p->mm == current->mm and make it the new owner.
> Exactly what sequence of clone() calls was used to cause the sharing
> isn't really relevant. I really think that a suitable candidate will
> be found amongst your children or your first sibling in 99.9% of those
> cases where more than one process is using an mm.
> 

Hmmm.. the 99.9% of the time is just guess work (not measured, could be possibly
true). I see and understand your code below. But before I try and implement
something like that, I was wondering why zap_threads() does not have that
heuristic. That should explain my inhibition.

Can anyone elaborate on zap_threads further?

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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