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

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Date:	Sun, 10 May 2009 22:56:27 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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

Hi


>> 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.

hmm
I don't think this patch change JIT behavior.
JIT makes large executable _anon_  pages. but page_mapping(anon-page)
return NULL.

Thus, the logic do nothing.


> 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.

true.
My SSD have high speed random reading charactastics.

> 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. My disks each do 50MBytes/second and even with the
> Gnome developers finest creations that ought to be enough if the rest of
> the system was working properly.

Yes, mesurement is essential.
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