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

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Message-Id: <20090508151532.6769e702.akpm@linux-foundation.org>
Date:	Fri, 8 May 2009 15:15:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	fengguang.wu@...el.com, hannes@...xchg.org, peterz@...radead.org,
	riel@...hat.com, linux-kernel@...r.kernel.org, tytso@....edu,
	linux-mm@...ck.org, elladan@...imo.com, npiggin@...e.de,
	cl@...ux-foundation.org, kosaki.motohiro@...fujitsu.com,
	minchan.kim@...il.com
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
 class citizen

On Fri, 8 May 2009 23:00:45 +0100
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > The patch seems reasonable but the changelog and the (non-existent)
> > design documentation could do with a touch-up.
> 
> Is it right that I as a user can do things like mmap my database
> PROT_EXEC to get better database numbers by making other
> stuff swap first ?
>
> You seem to be giving everyone a "nice my process up" hack.

Yep.

But prior to 2.6.27(?) the same effect could be had by mmap()ing the
file with or without PROT_EXEC.  The patch restores a
probably-beneficial heuristic which got lost in the LRU rewrite.

So we're no worse than pre-2.6.27 kernels here.  Plus there are
probably more effective ways of getting that sort of boost, such as
having a process running which simply touches your favoured pages
at a suitable (and fairly low) frequency.
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