linux-kernel - Re: swap-prefetch: A smart way to make good use of idle resources (was: updatedb)

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Date:	Fri, 27 Jul 2007 13:34:58 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Al Boldi <a1426z@...ab.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: swap-prefetch:  A smart way to make good use of idle resources
	(was: updatedb)

> IMHO, what everybody agrees on, is that swap-prefetch has a positive effect 
> in some cases, and nobody can prove an adverse effect (excluding power 
> consumption).  The reason for this positive effect is also crystal clear:  
> It prefetches from swap on idle into free memory, ie: it doesn't force 

the fact that there is free memory is ... strange. IN principle, Linux
keeps almost no memory free (except some emergency buffers) so that
things you swap in prematurely will BY DEFINITION go at the expense of
other things that could be there.... 

also, they take up seek time (5 to 10 msec), so if you were to read
something else at the time you get additional latency.

so the conclusion that it only can be better (if you don't care about
power) is imo premature.

Sure it still can be worth it, but it for sure is NOT an automatic
thing.

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