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

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Date:	Sat, 12 May 2007 18:21:47 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	Paul Jackson <pj@....com>
Cc:	nickpiggin@...oo.com.au, ray-lk@...rabbit.org, mingo@...e.hu,
	ck@....kolivas.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: swap prefetch improvements

On Saturday 12 May 2007 18:14, Paul Jackson wrote:
> > Ummm this is what I've been saying for over a year now but noone has been
> > listening.
>
> Well ... if there is a problem using prefetch and cpusets together,
> it doesn't look like the two of us are going to find it.
>
> I should probably look at your patch to answer this next question,
> but being a lazy retard, I'll just ask.  Is there a way, on a running
> system that has your prefetch patch configured in, to disable prefetch
> -- perhaps writing to some magic /proc file or something?

Indeed:

/proc/sys/vm/swap_prefetch

> If so, then how about you just remove the lines in the patch that
> disable prefetch on kernels configured with CPUSETS, and we charge
> ahead allowing both at the same time?

Ok so change the default value for swap_prefetch to 0 when CPUSETS is enabled? 
Sure, I can do that.

> If some day in the future I find something about prefetch that harms
> the HPC NUMA loads I care about, then I can just dynamically disable
> prefetch.
>
> If someone ever uncovers a real problem with prefetch and cpusets,
> then we will deal with it then.
>
> As to whether your patch is otherwise (other than cpusets) worthy
> of further acceptance, that I will have to leave up to those who are
> competent to make such judgements.

Thank you very much for your comments!

-- 
-ck
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