linux-kernel - Re: [patch 1/9] Guest page hinting: unused / free pages.

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Date:	Wed, 13 Sep 2006 16:59:03 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Hubertus Franke <frankeh@...son.ibm.com>,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	akpm@...l.org, nickpiggin@...oo.com.au, rhim@...gatech.edu
Subject: Re: [patch 1/9] Guest page hinting: unused / free pages.

On Wed, 2006-09-13 at 10:45 -0400, Rik van Riel wrote:
> > But another trouble you have not mentioned is what happens to pages
> > with pending make-volatile that need to and/or have been made stable
> > in the meantime. They too need to be removed from this pending list.
> 
> At the time where you walk the set of pages (pagevec?) to make
> volatile, you can check whether the page flags are still right.

A make volatile can be done anytime as long as the page is in page
cache. Before a page can be made stable the caller needs to make sure
that one of the conditions that prevent a make volatile becomes true.
So a page in the pending make-volatile array does not have to be removed
because a make stable has been done. It only has to be removed if it
gets freed.

> A page that was set to be marked volatile with the hypervisor,
> but later turned stable again would have that indicated in its
> page flags, right?

Several page flag bits and some other conditions like "has a mapping"
and "reference count is map count + 1". Most of the checks that need to
be done for make volatile are on page flags.

-- 
blue skies,
  Martin.

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.

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