linux-kernel - Re: [patch 5/5] Optimize page_mkclean

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Date:	Mon, 02 Jul 2007 09:07:26 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 5/5] Optimize page_mkclean_one

On Sun, 2007-07-01 at 15:27 +0200, Peter Zijlstra wrote:
> > But I could easily be overlooking something: Peter will recall.
> 
> /me tries to get his brain up to speed after the OLS closing party :-)

Oh-oh, the Black Thorn party :-)

> I did both pte_dirty and pte_write because I was extra careful. One
> _should_ imply the other, but since we'll be clearing both, I thought it
> prudent to also check both.

Just ran a little experiment: I've added a simple WARN_ON(ret == 0) to
page_mkclean after the page_test_dirty() check to see if there are cases
where the page is dirty and all ptes are read-only. A little stress run
including massive swap did not print a single warning.

> I will have to think on this a little more, but I'm currently of the
> opinion that the optimisation is not correct. But I'll have a thorough
> look at s390 again when I get home.

I think the patch is correct, although I beginning to doubt that is has
any effect.

-- 
blue skies,
  Martin.

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


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