linux-kernel - Re: [RFC PATCH 00/19] Foundation for automatic NUMA balancing

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Date:	Fri, 9 Nov 2012 15:42:57 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/19] Foundation for automatic NUMA balancing

Hi Mel,

On Tue, Nov 06, 2012 at 09:14:36AM +0000, Mel Gorman wrote:
> This series addresses part of the integration and sharing problem by
> implementing a foundation that either the policy for schednuma or autonuma
> can be rebased on. The actual policy it implements is a very stupid
> greedy policy called "Migrate On Reference Of pte_numa Node (MORON)".
> While stupid, it can be faster than the vanilla kernel and the expectation
> is that any clever policy should be able to beat MORON. The advantage is
> that it still defines how the policy needs to hook into the core code --
> scheduler and mempolicy mostly so many optimisations (s uch as native THP
> migration) can be shared between different policy implementations.

I haven't had much time to look into it yet, because I've been
attending KVM Forum the last few days, but this foundation looks ok
with me as a starting base and I ack it for merging it upstream. I'll
try to rebase on top of this and send you some patches.

> Patch 14 adds a MPOL_MF_LAZY mempolicy that an interested application can use.
> 	On the next reference the memory should be migrated to the node that
> 	references the memory.

This approach of starting with a stripped down foundation won't allow
for easy backportability anyway, so merging the userland API at the
first step shouldn't provide any benefit for the work that is ahead of
us. I would leave this for later and not part of the foundation.

All we need is a failsafe runtime and boot time turn off knob, just in
case.

Thanks,
Andrea
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