linux-kernel - Re: mm: used-once mapped file page detection

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Date:	Sun, 28 Feb 2010 21:36:27 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: mm: used-once mapped file page detection

On Sun, Feb 28, 2010 at 12:49:14PM -0500, Rik van Riel wrote:
> On 02/26/2010 09:32 AM, Johannes Weiner wrote:
> >On Wed, Feb 24, 2010 at 01:39:46PM -0800, Andrew Morton wrote:
> >>On Mon, 22 Feb 2010 20:49:07 +0100 Johannes Weiner<hannes@...xchg.org>  
> >>wrote:
> >>
> >>>This patch makes the VM be more careful about activating mapped file
> >>>pages in the first place.  The minimum granted lifetime without
> >>>another memory access becomes an inactive list cycle instead of the
> >>>full memory cycle, which is more natural given the mentioned loads.
> >>
> >>iirc from a long time ago, the insta-activation of mapped pages was
> >>done because people were getting peeved about having their interactive
> >>applications (X, browser, etc) getting paged out, and bumping the pages
> >>immediately was found to help with this subjective problem.
> >>
> >>So it was a latency issue more than a throughput issue.  I wouldn't be
> >>surprised if we get some complaints from people for the same reasons as
> >>a result of this patch.
> >
> >Agreed.  Although we now have other things in place to protect them once
> >they are active (VM_EXEC protection, lazy active list scanning).
> 
> You think we'll need VM_EXEC protection on the inactive list
> after your changes?

So far I personally did not experience anything that would indicate the
need for it.  But I would consider it an option if Andrew's worries turned
out to be true.
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