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Date: Wed, 21 Nov 2012 19:04:32 +0100
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 00/27] Latest numa/core release, v16
Message-ID: <20121121180432.GA29590@gmail.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>, Mel Gorman <mgorman@suse.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Paul Turner <pjt@google.com>, Lee Schermerhorn <Lee.Schermerhorn@hp.com>, Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Johannes Weiner <hannes@cmpxchg.org>, Hugh Dickins <hughd@google.com>


* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> [...] And not look at vsyscalls or anything, but look at what 
> schednuma does wrong!

I have started 4 independent lines of inquiry to figure out 
what's wrong on David's system, and all four are in the category 
of 'what does our tree do to cause a regression':

  - suboptimal (== regressive) 4K fault handling by numa/core

  - suboptimal (== regressive) placement by numa/core on David's 
    assymetric-topology system

  - vsyscalls escallating numa/core page fault overhead
    non-linearly

  - TLB flushes escallating numacore page fault overhead
    non-linearly

I have sent patches for 3 of them, one is still work in 
progress, because it's non-trivial.

I'm absolutely open to every possibility and obviously any 
regression is numa/core's fault, full stop.

What would you have done differently to handle this particular 
regression?

Thanks,

	Ingo

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