linux-kernel - Re: [PATCH] mm: swap prefetch improvements

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Date:	Tue, 22 May 2007 20:20:57 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	"Antonino Ingargiola" <tritemio@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Nick Piggin" <nickpiggin@...oo.com.au>,
	"Ray Lee" <ray-lk@...rabbit.org>, "ck list" <ck@....kolivas.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: swap prefetch improvements

On Tuesday 22 May 2007 20:15, Antonino Ingargiola wrote:
> 2007/5/21, Ingo Molnar <mingo@...e.hu>:
> > * Con Kolivas <kernel@...ivas.org> wrote:
> > > > A suggestion for improvement: right now swap-prefetch does a small
> > > > bit of swapin every 5 seconds and stays idle inbetween. Could this
> > > > perhaps be made more agressive (optionally perhaps), if the system
> > > > is not swapping otherwise? If block-IO level instrumentation is
> > > > needed to determine idleness of block IO then that is justified too
> > > > i think.
> > >
> > > Hmm.. The timer waits 5 seconds before trying to prefetch, but then
> > > only stops if it detects any activity elsewhere. It doesn't actually
> > > try to go idle in between but it doesn't take much activity to put it
> > > back to sleep, hence detecting yet another "not quite idle" period and
> > > then it goes to sleep again. I guess the sleep interval can actually
> > > be changed as another tunable from 5 seconds to whatever the user
> > > wanted.
> >
> > there was nothing else running on the system - so i suspect the swapin
> > activity flagged 'itself' as some 'other' activity and stopped? The
> > swapins happened in 4 bursts, separated by 5 seconds total idleness.
>
> I've noted burst swapins separated by some seconds of pause in my
> desktop system too (with sp_tester and an idle gnome).

That really is expected, as just about anything, including journal writeout, 
would be enough to put it back to sleep for 5 more seconds.
-- 
-ck
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