linux-kernel - Re: [PATCH 00/35] AutoNUMA alpha14

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Message-ID: <20120529160855.GD21339@redhat.com>
Date:	Tue, 29 May 2012 18:08:55 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Hillf Danton <dhillf@...il.com>,
	Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH 00/35] AutoNUMA alpha14

Hi,

On Tue, May 29, 2012 at 10:53:32AM -0500, Christoph Lameter wrote:
> then does the distribution of the load on its own. NUMA aware applications
> like that do not benefit and do not need either of the mechanisms proposed
> here.

Agreed. Who changes the apps to optimize things to that lowlevel, I
doubt wants to risk to hit on on a migrate on fault (or AutoNUMA async
migration for that matter).

> I think the proof that we need is that a general mix of applications
> actually benefits from an auto migration scheme. I would also like to see

Agreed.

> that it does no harm to existing NUMA aware applications.

As far as AutoNUMA is concerned, it will be a total bypass whenever
the mpol isn't MPOL_DEFAULT. So it shouldn't harm. Shared memory is
also bypassed.

It only alters the beahvior of MPOL_DEFAULT, any other kind of
mempolicy is unaffected, and all CPU bindings are also unaffected.

If an app has only a few vmas that are MPOL_DEFAULT those few will be
handled by AutoNUMA.

If people thinks AutoMigration is a better name I should rename
it. It's up to you. I thought using a "NUMA" suffix  would make it
more intuitive that if your hardware isn't NUMA, this won't do
anything at all. Migration as a feature isn't limited to NUMA (see
compaction etc..). Comments welcome.
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