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Date: Sun, 3 Aug 2003 17:20:03 -0700
From: David Schultz <das@FreeBSD.ORG>
To: "Dag-Erling =?us-ascii:iso-8859-1?Q?Sm=F8rgrav?=" <des@des.no>
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	<des@des.no>,	Poul-Henning Kamp <phk@phk.freebsd.dk>,
	Peter Jeremy <PeterJeremy@optushome.com.au>, arch@freebsd.org
References: <6955.1059728599@critter.freebsd.dk> <xzpel0568cn.fsf@dwp.des.no>
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cc: Peter Jeremy <PeterJeremy@optushome.com.au>
cc: Poul-Henning Kamp <phk@phk.freebsd.dk>
cc: arch@FreeBSD.ORG
Subject: Re: headsup: swap_pager.c
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On Fri, Aug 01, 2003, Dag-Erling Smrgrav wrote:
> "Poul-Henning Kamp" <phk@phk.freebsd.dk> writes:
> > The thing you overlook is that often when things gets paged out, the
> > system is short on memory and therefore more likely to not do anything
> > productive, whereas when things gets paged in, there are a better chance
> > of some other process being able to use the CPU time productively.
> > If we did predictive pageouts like some of the "serious" mainfram OS's
> > this would be less true.
> 
> How hard would it be to get the kernel to write the pages "most likely
> to be swapped out" to swap in the idle loop, to save time if / when
> they actually need to be swapped out later?
> 
> I thought we already did this to some extent (ref. FAQ 16.1), but
> apparently I was wrong?

FreeBSD already does that.  ;-)  You can control the number of
clean pages that it keeps around with the sysctls
vm.v_cache_{min,max}, but you shouldn't need to tune anything to
get good performance.  FWIW, the stuff phk is working on is
in a different area; it has to do with what swap device your
pages wind up on after the VM system has already decided to
write them out.