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Date: Mon, 7 Apr 2014 20:19:10 +0400 From: Cyrill Gorcunov <gorcunov@...il.com> To: Mel Gorman <mgorman@...e.de> Cc: David Vrabel <david.vrabel@...rix.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Peter Anvin <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>, Steven Noonan <steven@...inklabs.net>, 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 Mon, Apr 07, 2014 at 04:49:35PM +0100, Mel Gorman wrote: > On Mon, Apr 07, 2014 at 04:32:39PM +0100, David Vrabel wrote: > > On 07/04/14 16:10, Mel Gorman wrote: > > > _PAGE_NUMA is currently an alias of _PROT_PROTNONE to trap NUMA hinting > > > faults. As the bit is shared care is taken that _PAGE_NUMA is only used in > > > places where _PAGE_PROTNONE could not reach but this still causes problems > > > on Xen and conceptually difficult. > > > > The problem with Xen guests occurred because mprotect() /was/ confusing > > PROTNONE mappings with _PAGE_NUMA and clearing the non-existant NUMA hints. > > I didn't bother spelling it out in case I gave the impression that I was > blaming Xen for the problem. As the bit is now changes, does it help > the Xen problem or cause another collision of some sort? There is no > guarantee _PAGE_NUMA will remain as bit 62 but at worst it'll use bit 11 > and NUMA_BALANCING will depend in !KMEMCHECK. Fwiw, we're using bit 11 for soft-dirty tracking, so i really hope worst case never happen. (At the moment I'm trying to figure out if with this set it would be possible to clean up ugly macros in pgoff_to_pte for 2 level pages). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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