linux-kernel - Re: [PATCH 2/3] x86: Define _PAGE_NUMA with unused physical address bits PMD and PTE levels

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Message-ID: <20140409150935.GC10526@twins.programming.kicks-ass.net>
Date:	Wed, 9 Apr 2014 17:09:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Steven Noonan <steven@...inklabs.net>,
	Mel Gorman <mgorman@...e.de>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux-MM <linux-mm@...ck.org>, Linux-X86 <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH 2/3] x86: Define _PAGE_NUMA with unused physical address
 bits PMD and PTE levels

On Wed, Apr 09, 2014 at 11:04:48AM -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Apr 08, 2014 at 01:59:09PM -0700, H. Peter Anvin wrote:
> > On 04/08/2014 01:51 PM, Steven Noonan wrote:
> > > On Tue, Apr 8, 2014 at 8:16 AM, H. Peter Anvin <hpa@...or.com> wrote:
> > >> <snark>
> > >>
> > >> Of course, it would also be preferable if Amazon (or anything else) didn't need Xen PV :(
> > > 
> > > Well Amazon doesn't expose NUMA on PV, only on HVM guests.
> > > 
> > 
> > Yes, but Amazon is one of the main things keeping Xen PV alive as far as
> > I can tell, which means the support gets built in, and so on.
> 
> Taking the snarkiness aside, the issue here is that even on guests
> without NUMA exposed the problem shows up. That is the 'mknuma' are
> still being called even if the guest topology is not NUMA!
> 
> Which brings a question - why isn't the mknuma and its friends gatted by
> an jump_label machinery or such?
> 
> Mel, any particular reasons why it couldn't be done this way?

Hmm,. I thought we disabled all that when there was only the 1 node. All
this should be driven from task_tick_numa() which only gets called when
numabalancing_enabled, and that _should_ be false when nr_nodes == 1.
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