linux-kernel - Re: Populating multiple ptes at fault time

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Message-ID: <48D2EBBB.205@goop.org>
Date:	Thu, 18 Sep 2008 17:00:59 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Avi Kivity <avi@...hat.com>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickens <hugh@...itas.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...ranet.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: Populating multiple ptes at fault time

Avi Kivity wrote:
>> Yes.  At worst Linux would underestimate the process RSS a bit
>> (depending on how many unsynchronized ptes you leave lying around).  I
>>   
>
> Not the RSS (that's pte.present pages) but the working set (aka active
> list).

Yep.

>> bet there's an appropriate pvop hook you could use to force
>> synchronization just before the kernel actually inspects the bits
>> (leaving lazy mode sounds good).
>>   
>
> It would have to be a new lazy mode, not the existing one, I think.

The only direct use of pte_young() is in zap_pte_range, within a
mmu_lazy region.  So syncing the A bit state on entering lazy mmu mode
would work fine there.

The call via page_referenced_one() doesn't seem to have a very
convenient hook though.  Perhaps putting something in
page_check_address() would do the job.

    J
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