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

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Date:	Tue, 22 May 2007 22:31:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Michael Chang <thenewme91@...il.com>
Cc:	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ray Lee <ray-lk@...rabbit.org>, linux-kernel@...r.kernel.org,
	ck list <ck@....kolivas.org>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [ck] Re: [PATCH] mm: swap prefetch improvements


* Michael Chang <thenewme91@...il.com> wrote:

> > It clearly should not consider 'itself' as IO activity. This 
> > suggests some bug in the 'detect activity' mechanism, agreed? I'm 
> > wondering whether you are seeing the same problem, or is all 
> > swap-prefetch IO on your system continuous until it's done [or some 
> > other IO comes inbetween]?
> 
> The only "problem" I can see with this idea is in the potential case 
> that it takes up all the IO activity, and so there is never enough IO 
> activity from other progams to trigger the wait mechanism because they 
> don't get a chance to run.

i dont understand what you mean. Any 'use only idle IO capacity' 
mechanism should immediately cease to be active the moment any other app 
tries to do IO - whether the IO subsystem is saturated or not.

> That said, I don't think there are any issues with the code 
> compensating for its own activity in the "detect activity" mechanism 
> -- assuming there wasn't a major impact in e.g. maintainability or 
> something.
> 
> As for the burstyness... considering the "no negative impact" stance, 
> I can understand that. But it seems inefficient, at best...

well, it's a plain old bug (a not too serious one) in my book, i'm 
surprised that we are now at mail #7 about it :-) I reported it, and i 
guess Con will fix it eventually. There's really no need to deny that it 
exists or to try to talk it out of existence. Sheesh! :-)

	Ingo
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