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Date: Mon, 24 Mar 2008 10:46:43 -0700
From: "Paul Menage" <menage@google.com>
To: balbir@linux.vnet.ibm.com
Subject: Re: [RFC][-mm] Memory controller add mm->owner
Cc: linux-mm@kvack.org, "Hugh Dickins" <hugh@veritas.com>,
       "Sudhir Kumar" <skumar@linux.vnet.ibm.com>,
       "YAMAMOTO Takashi" <yamamoto@valinux.co.jp>, lizf@cn.fujitsu.com,
       linux-kernel@vger.kernel.org, taka@valinux.co.jp,
       "David Rientjes" <rientjes@google.com>,
       "Pavel Emelianov" <xemul@openvz.org>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>
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On Mon, Mar 24, 2008 at 10:33 AM, Balbir Singh
<balbir@linux.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