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

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Message-id: <004501c9eb60$a9abb4c0$fd031e40$@rwth-aachen.de>
Date:	Fri, 12 Jun 2009 15:21:15 +0200
From:	Stefan Lankes <lankes@...s.rwth-aachen.de>
To:	'Brice Goglin' <Brice.Goglin@...ia.fr>
Cc:	'Andi Kleen' <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Lee.Schermerhorn@...com, linux-numa@...r.kernel.org,
	Boris Bierbaum <boris@...s.rwth-aachen.de>
Subject: RE: [RFC PATCH 0/4]: affinity-on-next-touch

> 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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