linux-kernel - Re: [-mm] Add an owner to the mm

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Date:	Sat, 5 Apr 2008 10:23:33 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"Pavel Emelianov" <xemul@...nvz.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,
	linux-mm@...ck.org, "David Rientjes" <rientjes@...gle.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [-mm] Add an owner to the mm_struct (v8)

On Sat, Apr 5, 2008 at 7:47 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>
>  Repeating my question earlier
>
>  Can we delay setting task->cgroups = &init_css_set for the group_leader, until
>  all threads have exited?

Potentially, yes. It also might make more sense to move the
exit_cgroup() for all threads to a later point rather than special
case delayed group leaders.

> If the user is unable to remove a cgroup node, it will
>  be due a valid reason, the group_leader is still around, since the threads are
>  still around. The user in that case should wait for notify_on_release.
>
>  >
>  > To me, it seems that setting up a *virtual address space* cgroup
>  > hierarchy and then putting half your threads in one group and half in
>  > the another is asking for trouble. We need to not break in that
>  > situation, but I'm not sure it's a case to optimize for.
>
>  That could potentially happen, if the virtual address space cgroup and cpu
>  control cgroup were bound together in the same hierarchy by the sysadmin.

Yes, I agree it could potentially happen. But it seems like a strange
thing to do if you're planning to be not have the same groupings for
cpu and va.

>
>  I measured the overhead of removing the delay_group_leader optimization and
>  found a 4% impact on throughput (with volanomark, that is one of the
>  multi-threaded benchmarks I know of).

Interesting, I thought (although I've never actually looked at the
code) that volanomark was more of a scheduling benchmark than a
process start/exit benchmark. How frequently does it have processes
(not threads) exiting?

How many runs was that over? Ingo's recently posted volanomark tests
against -rc7 showed ~3% random variation between runs.

Paul
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