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

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Message-ID: <6599ad830803241046l61e2965t52fd28e165d5df7a@mail.gmail.com>
Date:	Mon, 24 Mar 2008 10:46:43 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	balbir@...ux.vnet.ibm.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

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

Paul
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