linux-kernel - Re: updatedb

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Date:	Fri, 27 Jul 2007 13:48:00 +0200
From:	Mike Galbraith <efault@....de>
To:	Rene Herman <rene.herman@...il.com>
Cc:	Jesper Juhl <jesper.juhl@...il.com>,
	Andika Triwidada <andika@...il.com>,
	Robert Deaton <false.hopes@...il.com>,
	linux-kernel@...r.kernel.org, ck list <ck@....kolivas.org>,
	linux-mm@...ck.org, B.Steinbrink@....de,
	Andrew Morton <akpm@...l.org>
Subject: Re: updatedb

On Fri, 2007-07-27 at 13:09 +0200, Rene Herman wrote:
> On 07/27/2007 11:26 AM, Mike Galbraith wrote:
> 

> > Updatedb finishes, freeing some ram (doesn't matter how much)
> 
> Will be very little and swap-prefetch at least in its current form needs 
> more than very little to start doing anything:
> 
> http://ck.kolivas.org/patches/swap-prefetch/2.6.21-swap_prefetch-38.patch
> 
> | /*
> |  * Set max number of entries to 2/3 the size of physical ram  as we
> |  * only ever prefetch to consume 2/3 of the ram.
> |  */
> 
> However, okay, let's just ignore that and pretend it kicks in even with the 
> little free memory updatedb itself left behind when it finished:

Hm.  I didn't read the patch, so I'm only going on what you quoted.
>>From that, all I see is a limit on how much will be used total, and 2/3
of physical ram is a bunch.  This quote doesn't say free ram, it says
physical ram.  If it really does use only free ram, that indeed sounds
pretty pointless.  I believe the users who say their apps really do get
paged back in though, so suspect that's not the case.

Anyway, I only offered a simple explanation of how swap-prefetching can
indeed help (and possibly hurt) with something like updatedb, not an
analysis of it's current implementation ;-)  I'd have to read it, and
test it myself to do that, but my world doesn't have a need for it,
so...

	-Mike

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