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

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Date:	Wed, 9 Apr 2014 16:39:17 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Steven Noonan <steven@...inklabs.net>,
	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>,
	Peter Zijlstra <peterz@...radead.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 11:18:27AM -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Apr 08, 2014 at 05:51:23PM +0100, Mel Gorman wrote:
> > On Tue, Apr 08, 2014 at 12:02:50PM -0400, Konrad Rzeszutek Wilk wrote:
> > > .snip..
> > > > >>> David Vrabel has a patchset which I presumed would be pulled through
> > > > >the
> > > > >>> Xen tree this merge window:
> > > > >>>
> > > > >>> [PATCHv5 0/8] x86/xen: fixes for mapping high MMIO regions (and
> > > > >remove
> > > > >>> _PAGE_IOMAP)
> > > > >>>
> > > > >>> That frees up this bit.
> > > > >>>
> > > > >>
> > > > >> Thanks, I was not aware of that patch.  Based on it, I intend to
> > > > >force
> > > > >> automatic NUMA balancing to depend on !XEN and see what the reaction
> > > > >is. If
> > > > >> support for Xen is really required then it potentially be re-enabled
> > > > >if/when
> > > > >> that series is merged assuming they do not need the bit for something
> > > > >else.
> > > > >>
> > > > >
> > > > >Amazon EC2 does have large memory instance types with NUMA exposed to
> > > > >the guest (e.g. c3.8xlarge, i2.8xlarge, etc), so it'd be preferable
> > > > >(to me anyway) if we didn't require !XEN.
> > > 
> > > What about the patch that David Vrabel posted:
> > > 
> > > http://osdir.com/ml/general/2014-03/msg41979.html
> > > 
> > > Has anybody taken it for a spin?
> > 
> > Alternatively "[PATCH 4/5] mm: use paravirt friendly ops for NUMA
> > hinting ptes" which modifies the NUMA pte helpers instead of the main
> > set/clear ones.
> 
> Ah nice! Looking forward to it being posted as non-RFC and could you also
> please CC 'xen-devel@...ts.xenproject.org' on it?
> 

Yes I will. Unless the x86 maintainers push for it on the grounds that
it is a functional fix for xen, I'm going to wait until after the merge
window to resend it. That'd give it some chance of being tested in -next
before hitting mainline.

-- 
Mel Gorman
SUSE Labs
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