linux-kernel - Re: [PATCH 3/3][RFC] swsusp: shrink file cache first

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Message-ID: <20090206080354.GA6516@barrios-desktop>
Date:	Fri, 6 Feb 2009 17:03:54 +0900
From:	MinChan Kim <minchan.kim@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/3][RFC] swsusp: shrink file cache first

Hi, Johannes.
I have some questions.
Just out of curiosity. :)

On Fri, Feb 06, 2009 at 04:11:28AM +0100, Johannes Weiner wrote:
> File cache pages are saved to disk either through normal writeback by
> reclaim or by including them in the suspend image written to a
> swapfile.
> 
> Writing them either way should take the same amount of time but doing
> normal writeback and unmap changes the fault behaviour on resume from
> prefault to on-demand paging, smoothening out resume and giving

What do you mean "unmap"? 
Why normal writeback and unmap chnages the fault behavior on resume ?

> previously cached pages the chance to stay out of memory completely if
> they are not used anymore.
> 
> Another reason for preferring file page eviction is that the locality
> principle is visible in fault patterns and swap might perform really
> bad with subsequent faulting of contiguously mapped pages.

Why do you think that swap might perform bad with subsequent faulting 
of contiguusly mapped page ?
You mean normal file system is faster than swap due to readahead and 
smart block of allocation ?


-- 
Kinds Regards
MinChan Kim

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