linux-kernel - Re: RFT: updatedb "morning after" problem [was: Re: -mm merge plans for 2.6.23]

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Date:	Sun, 29 Jul 2007 18:53:17 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Rene Herman <rene.herman@...il.com>
Cc:	Ray Lee <ray-lk@...rabbit.org>, david@...g.hm,
	Daniel Hazelton <dhazelton@...er.net>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frank Kingswood <frank@...gswood-consulting.co.uk>,
	Andi Kleen <andi@...stfloor.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Jesper Juhl <jesper.juhl@...il.com>,
	ck list <ck@....kolivas.org>, Paul Jackson <pj@....com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: RFT: updatedb "morning after" problem [was: Re: -mm merge plans
 for 2.6.23]

> > Is that generally the case on your systems? Every linux system I've
> > run, regardless of RAM, has always pushed things out to swap.
> 
> For me, it is generally the case yes. We are still discussing this in the 
> context of desktop machines and their problems with being slow as things 
> have been swapped out and generally I expect a desktop to have plenty of 
> swap which it's not regularly going to fillup significantly since then the 
> machine's unworkably slow as a desktop anyway.

A simple log optimises writeout (which is latency critical) and can
otherwise stall an enitre system. In a log you can also have multiple
copies of the same page on disk easily, some stale - so you can write out
chunks of data that are not all them removed from memory, just so you get
them back more easily if you then do (and I guess you'd mark them
accordingly)

The second element is a cleaner - something to go around removing stuff
from the log that is needed when the disks are idle - and also to repack
data in nice linear chunks. So instead of using the empty disk time for
page-in you use it for packing data and optimising future paging.

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