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

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Date:	Sun, 10 May 2009 11:07:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>, hannes@...xchg.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, minchan.kim@...il.com
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
 class  citizen

On Sun, 2009-05-10 at 17:59 +0900, KOSAKI Motohiro wrote:
> 2009/5/9 Alan Cox <alan@...rguk.ukuu.org.uk>:
> >> 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.
> 
> How about this?
> if priority < DEF_PRIORITY-2, aggressive lumpy reclaim in
> shrink_inactive_list() already
> reclaim the active page forcely.
> then, this patch don't change kernel reclaim policy.
> 
> anyway, user process non-changable preventing "nice my process up
> hack" seems makes sense to me.
> 
> test result:
> 
> echo 100 > /proc/sys/vm/dirty_ratio
> echo 100 > /proc/sys/vm/dirty_background_ratio
> run modified qsbench (use mmap(PROT_EXEC) instead malloc)
> 
>            active2active vs active2inactive ratio
> before    5:5
> after       1:9
> 
> please don't ask performance number. I haven't reproduce Wu's patch
> improvemnt ;)
> 
> Wu, What do you think?

I don't think this is desirable, like Andrew already said, there's tons
of ways to defeat any of this and we've so far always priorized mappings
over !mappings. Limiting this to only PROT_EXEC mappings is already less
than it used to be.

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