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Re: [regression v4.0-rc1] mm: IPIs from TLB flushes causing significant

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [regression v4.0-rc1] mm: IPIs from TLB flushes causing significant performance degradation.
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Mon, 2 Mar 2015 22:56:14 -0800
Cc: Mel Gorman <mgorman@xxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Matt B <jackdachef@xxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, linux-mm <linux-mm@xxxxxxxxx>, xfs@xxxxxxxxxxx
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On Mon, Mar 2, 2015 at 9:20 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>>
>> But are those migrate-page calls really common enough to make these
>> things happen often enough on the same pages for this all to matter?
>
> It's looking like that's a possibility.

Hmm. Looking closer, commit 10c1045f28e8 already should have
re-introduced the "pte was already NUMA" case.

So that's not it either, afaik. Plus your numbers seem to say that
it's really "migrate_pages()" that is done more. So it feels like the
numa balancing isn't working right.

But I'm not seeing what would cause that in that commit. It really all
looks the same to me. The few special-cases it drops get re-introduced
later (although in a different form).

Mel, do you see what I'm missing?

                     Linus

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