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

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Date:	Sun, 10 May 2009 10:51:52 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>, hannes@...xchg.org,
	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

Alan Cox wrote:
> On Sun, 10 May 2009 18:36:19 +0900
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
>> I don't oppose this policy. PROT_EXEC seems good viewpoint.
> 
> I don't think it is that simple
> 
> Not only can it be abused but some systems such as java have large
> PROT_EXEC mapped environments, as do many other JIT based languages.

On the file LRU side, or on the anon LRU side?

> Secondly it moves the pressure from the storage volume holding the system
> binaries and libraries to the swap device which already has to deal with
> a lot of random (and thus expensive) I/O, as well as the users filestore
> for mapped objects there - which may even be on a USB thumbdrive.

Preserving the PROT_EXEC pages over streaming IO should not
move much (if any) pressure from the file LRUs onto the
swap-backed (anon) LRUs.

> I still think the focus is on the wrong thing. We shouldn't be trying to
> micro-optimise page replacement guesswork - we should be macro-optimising
> the resulting I/O performance.

Any ideas on how to achieve that? :)

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