linux-kernel - Re: [RFC PATCH 0/4]: affinity-on-next-touch

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Date:	Mon, 22 Jun 2009 19:06:25 +0200
From:	Brice Goglin <Brice.Goglin@...ia.fr>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
CC:	Stefan Lankes <lankes@...s.rwth-aachen.de>,
	'Andi Kleen' <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, linux-numa@...r.kernel.org,
	Boris Bierbaum <boris@...s.rwth-aachen.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [RFC PATCH 0/4]: affinity-on-next-touch

Lee Schermerhorn wrote:
> The primary difference should be at unmap time, right?  In the fault
> path, I only update the pte of the faulting task.  That's why I require
> the [anon] pages to be in the swap cache [or something similar].  I
> don't want to be fixing up other tasks' page tables in the context of
> the faulting task's fault handler.  If, later, another task touches the
> page, it will take a minor fault and find the [possibly migrated] page
> in the cache.  Hmmm, I guess all tasks WILL incur the minor fault if
> they touch the page after the unmap.  That could be part of the
> difference if you compare on the same kernel version.
>   

Agreed.

> Try booting with cgroup_disable=memory on the command line, if you have
> the memory resource controller configured in.  See what that does to
> your measurements.
>   

It doesn't seem to help. I'll try to bisect and find where the
performance dropped.

> ??? I would expect low level page copying to be highly optimized per
> arch, and also fairly stable.

I just did a quick copy_page benchmark and didn't see any performance
difference between 2.6.27 and mmotm.

thanks,
Brice

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