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From: Stefan Lankes <lankes@lfbs.rwth-aachen.de>
To: "'Brice Goglin'" <Brice.Goglin@inria.fr>
Cc: "'Andi Kleen'" <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       Lee.Schermerhorn@hp.com, linux-numa@vger.kernel.org,
       Boris Bierbaum <boris@lfbs.rwth-aachen.de>
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 <004001c9eb53$71991300$54cb3900$@rwth-aachen.de> <4A324A4E.1060405@inria.fr>
In-reply-to: <4A324A4E.1060405@inria.fr>
Subject: RE: [RFC PATCH 0/4]: affinity-on-next-touch
Date: Fri, 12 Jun 2009 15:21:15 +0200
Organization: Chair for Operating Systems, RWTH Aachen University
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> So mbind(MPOL_MF_LAZY) is taking care of changing page protection so as
> to generate page-faults on next-touch? (instead of your madvise)
> Is it migrating the whole memory area? Or only single pages?

mbind removes the pte references. Page migration will occur, when a task
access to one of these unmapped pages. Therefore, Lee's solution migrate one
single page and not the whole area.

You find further information at slides 19-23 of
http://mirror.linux.org.au/pub/linux.conf.au/2007/video/talks/197.pdf. 

> Then, what's happening with MPOL_MF_LAZY in the kernel? Is it actually
> stored in the mempolicy? If so, couldn't another fault later cause
> another migration?
> Or is MPOL_MF_LAZY filtered out of the policy once the protection of
> all
> PTE has been changed?
>
> I don't see why we need a new mempolicy here. If we are migrating
> single
> pages, migrate-on-next-touch looks like a page-attribute to me. There
> should be nothing to store in a mempolicy/VMA/whatever.
> 

MPOL_MF_LAZY is used as flag and does not specify a new policy. Therefore,
MPOL_MF_LAZY isn't stored in a VMA. The flag is only used to detect that the
system call mbind has to unmap these pages.

Stefan

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