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

From: Brice Goglin <Brice.Goglin@inria.fr>
To: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Stefan Lankes <lankes@lfbs.rwth-aachen.de>,
	"'Andi Kleen'" <andi@firstfloor.org>,
	linux-kernel@vger.kernel.org, linux-numa@vger.kernel.org,
	Boris Bierbaum <boris@lfbs.rwth-aachen.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Balbir Singh <balbir@linux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [RFC PATCH 0/4]: affinity-on-next-touch
Date: Mon, 22 Jun 2009 19:06:25 +0200	[thread overview]
Message-ID: <4A3FBA11.8030304@inria.fr> (raw)
In-Reply-To: <1245689724.7799.124.camel@lts-notebook>

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