Re: [PATCH] mm: swap prefetch improvements

From: Con Kolivas <kernel@xxxxxxxxxxx>
Date: Sat, 12 May 2007 17:28:34 +1000

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.

--
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Follow-Ups:
- Re: [PATCH] mm: swap prefetch improvements
  - From: Paul Jackson

References:
- 2.6.22 -mm merge plans
  - From: Andrew Morton
- Re: [PATCH] mm: swap prefetch improvements
  - From: Con Kolivas
- Re: [PATCH] mm: swap prefetch improvements
  - From: Paul Jackson

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Relevant Pages

[PATCH] mm: Implement Swap Prefetching v22
... Here's a significant rewrite of the swap prefetching code. ... I have tested it on my own hardware and build tested numerous numa ... extern unsigned int nr_swapfiles; ...
(Linux-Kernel)
Re: [PATCH] mm: swap prefetch improvements
... Con wrote: ... 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 ...
(Linux-Kernel)