linux-kernel - Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for _PAGE

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Date:	Wed, 09 Apr 2014 16:34:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Mel Gorman <mgorman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux-X86 <x86@...nel.org>, Cyrill Gorcunov <gorcunov@...il.com>,
	Steven Noonan <steven@...inklabs.net>,
	Rik van Riel <riel@...hat.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for _PAGE_NUMA
 v2

On 04/08/2014 11:21 PM, Ingo Molnar wrote:
> 
> I think the real underlying objection was that PTE_NUMA was the last 
> leftover from AutoNUMA, and removing it would have made it not a 
> 'compromise' patch set between 'AutoNUMA' and 'sched/numa', but would 
> have made the sched/numa approach 'win' by and large.
> 
> The whole 'losing face' annoyance that plagues all of us (me 
> included).
> 
> I didn't feel it was important to the general logic of adding access 
> pattern aware NUMA placement logic to the scheduler, and I obviously 
> could not ignore the NAKs from various mm folks insisting on PTE_NUMA, 
> so I conceded that point and Mel built on that approach as well.
> 
> Nice it's being cleaned up, and I'm pretty happy about how NUMA 
> balancing ended up looking like.
> 

How painful would it be to get rid of _PAGE_NUMA entirely?  Page bits
are a highly precious commodity and saving one would be valuable.

	-hpa


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