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

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Date:	Sat, 12 May 2007 17:28:34 +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 15:51, Paul Jackson wrote:
> Con wrote:
> > Hmm I'm not really sure what it takes to make it cpuset aware;
> > ...
> > It is numa aware to some degree. It stores the node id and when it starts
> > prefetching it only prefetches to nodes that are suitable for prefetching
> > to ...
> > It would be absolutely trivial to add a check for 'number_of_cpusets' <=
> > 1 in  the prefetch_enabled() function. Would you like that?
>
> Hmmm ... it seems that we shadow boxing here ... trying to pick a solution
> to solve a problem when we aren't even sure we have a problem, much less
> what the problem is.
>
> That does not usually lead to the right path.
>
> Could you put some more effort into characterizing what problems
> can arise if one has prefetch and cpusets active at the same time?
>
> My first wild guess is that the only incompatibility would have been that
> prefetch might mess up NUMA placement (get pages on wrong nodes), which
> it seems you have tried to address in your current patches.  So it would
> not surprise me if there was no problem here.

Ummm this is what I've been saying for over a year now but noone has been 
listening.

> We may just have to lean on Nick some more, if he is the only one who
> understands what the problem is, to try again to explain it to us.

-- 
-ck
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