linux-kernel - Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

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Date:	Thu, 07 May 2009 16:15:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Elladan <elladan@...imo.com>, Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
 class citizen

On Thu, 2009-05-07 at 09:39 -0400, Christoph Lameter wrote:
> On Thu, 7 May 2009, Wu Fengguang wrote:
> 
> > Introduce AS_EXEC to mark executables and their linked libraries, and to
> > protect their referenced active pages from being deactivated.
> 
> 
> We already have support for mlock(). How is this an improvement? This is
> worse since the AS_EXEC pages stay on the active list and are continually
> rescanned.

It re-instates the young bit for PROT_EXEC pages, so that they will only
be paged when they are really cold, or there is severe pressure.

This simply gives them an edge over regular data. I don't think the
extra scanning is a problem, since you rarely have huge amounts of
executable pages around.

mlock()'ing all code just doesn't sound like a good alternative.
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