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 14:12:15 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Rene Herman <rene.herman@...il.com>
Cc:	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>,
	Ray Lee <ray-lk@...rabbit.org>,
	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]

> Contrived thing and all, but what it does do is show exactly how bad seeking 
> all over swap-space is. If you push it out before hitting enter, the time it 
> takes easily grows past 10 minutes (with my 768M) versus sub-second (!) when 
> it's all in to start with.

Think in "operations/second" and you get a better view of the disk.

> What are the tradeoffs here? What wants small chunks? Also, as far as I'm 
> aware Linux does not do things like up the granularity when it notices it's 
> swapping in heavily? That sounds sort of promising...

Small chunks means you get better efficiency of memory use - large chunks
mean you may well page in a lot more than you needed to each time (and
cause more paging in turn). Your disk would prefer you fed it big linear
I/O's - 512KB would probably be my first guess at tuning a large box
under load for paging chunk size.

More radically if anyone wants to do real researchy type work - how about
log structured swap with a cleaner  ?

Alan
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