linux-kernel - Re: [PATCH] emulate accessed bit for EPT

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Date:	Fri, 5 Feb 2010 15:34:23 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Rik van Riel <riel@...hat.com>, balbir@...ux.vnet.ibm.com,
	jdike@...toit.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [PATCH] emulate accessed bit for EPT

On Thu, Feb 04, 2010 at 06:47:15PM +0100, Andrea Arcangeli wrote:
> On Thu, Feb 04, 2010 at 08:40:43AM -0500, Rik van Riel wrote:
> > I suspect it won't be very many. I have been monitoring
> > /proc/meminfo on my system while testing this patch, and
> > it is quite typical that the size of the inactive anon
> > list does not change for minutes at a time.
> > 
> > In other words, no pages are moved onto or off of the
> > inactive anon list for several minutes. That corresponds
> > to a very small number of minor faults introduced by my
> > patch.
> 
> When there's light VM pressure, ideally there should be zero overhead
> caused by the patch. When there is VM pressure this will avoid some
> unnecessary I/O which should outweight the minor faults. It should be
> a good default behavior.

Agree.

But perhaps a module parameter to turn accessed bit emulation off might
be handy in the future?

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