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

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Message-ID: <47E8E4F3.6090604@linux.vnet.ibm.com>
Date:	Tue, 25 Mar 2008 17:11:39 +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 Mon, Mar 24, 2008 at 10:33 AM, Balbir Singh
> <balbir@...ux.vnet.ibm.com> wrote:
>>  > OK, so we don't need to handle this for NPTL apps - but for anything
>>  > still using LinuxThreads or manually constructed clone() calls that
>>  > use CLONE_VM without CLONE_PID, this could still be an issue.
>>
>>  CLONE_PID?? Do you mean CLONE_THREAD?
> 
> Yes, sorry - CLONE_THREAD.
> 
>>  For the case you mentioned, mm->owner is a moving target and we don't want to
>>  spend time finding the successor, that can be expensive when threads start
>>  exiting one-by-one quickly and when the number of threads are high. I wonder if
>>  there is an efficient way to find mm->owner in that case.
>>
> 
> But:
> 
> - running a high-threadcount LinuxThreads process is by definition
> inefficient and expensive (hence the move to NPTL)
> 
> - any potential performance hit is only paid at exit time
> 
> - in the normal case, any of your children or one of your siblings
> will be a suitable alternate owner
> 
> - in the worst case, it's not going to be worse than doing a
> for_each_thread() loop
> 
> so I don't think this would be a major problem
> 

I've been looking at zap_threads, I suspect we'll end up implementing a similar
loop, which makes me very uncomfortable. Adding code for the least possible
scenario. It will not get invoked for CLONE_THREAD, but will get invoked for the
case when CLONE_VM is set without CLONE_THREAD.

I'll try and experiment a bit more and see what I come up with


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