linux-kernel - Re: [patch 4/6] Guest page hinting: writable page table entries.

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Message-ID: <49D37E21.2000609@redhat.com>
Date:	Wed, 01 Apr 2009 10:45:53 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, frankeh@...son.ibm.com,
	akpm@...l.org, nickpiggin@...oo.com.au, hugh@...itas.com
Subject: Re: [patch 4/6] Guest page hinting: writable page table entries.

Martin Schwidefsky wrote:
> On Wed, 01 Apr 2009 09:25:34 -0400
> Rik van Riel <riel@...hat.com> wrote:
> 
>> Martin Schwidefsky wrote:
>>
>> This code has me stumped.  Does it mean that if a page already
>> has the PageWritable bit set (and count_ok stays 0), we will
>> always mark the page as volatile?
>>
>> How does that work out on !s390?
> 
> No, we will not always mark the page as volatile. If PG_writable is
> already set count_ok will stay 0 and a call to page_make_volatile is
> done. This differs from page_set_volatile as it repeats all the
> required checks, then calls page_set_volatile with a PageWritable(page)
> as second argument. What state the page will get depends on the
> architecture definition of page_set_volatile. For s390 this will do a
> state transition to potentially volatile as the PG_writable bit is set.
> On architecture that cannot check the dirty bit on a physical page basis
> you need to make the page stable.

Good point. I guess that means patch 4/6 checks out right, then :)

Acked-by: Rik van Riel <riel@...hat.com>

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