linux-kernel - Re: [PATCH 05/40] autonuma: define _PAGE_NUMA_PTE and _PAGE_NUMA

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Date:	Thu, 28 Jun 2012 17:00:46 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Don Morris <don.morris@...com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 05/40] autonuma: define _PAGE_NUMA_PTE and _PAGE_NUMA_PMD

Hi Don,

On Thu, Jun 28, 2012 at 08:13:11AM -0700, Don Morris wrote:
> On 06/28/2012 05:55 AM, Andrea Arcangeli wrote:
> > We will set these bitflags only when the pmd and pte is non present.
> > 
> 
> Just a couple grammar nitpicks.
> 
> > They work like PROT_NONE but they identify a request for the numa
> > hinting page fault to trigger.
> > 
> > Because we want to be able to set these bitflag in any established pte
> 
> these bitflags
> 
> > or pmd (while clearing the present bit at the same time) without
> > losing information, these bitflags must never be set when the pte and
> > pmd are present.
> > 
> > For _PAGE_NUMA_PTE the pte bitflag used is _PAGE_PSE, which cannot be
> > set on ptes and it also fits in between _PAGE_FILE and _PAGE_PROTNONE
> > which avoids having to alter the swp entries format.
> > 
> > For _PAGE_NUMA_PMD, we use a reserved bitflag. pmds never contain
> > swap_entries but if in the future we'll swap transparent hugepages, we
> > must keep in mind not to use the _PAGE_UNUSED2 bitflag in the swap
> > entry format and to start the swap entry offset above it.
> > 
> > PAGE_UNUSED2 is used by Xen but only on ptes established by ioremap,
> > but it's never used on pmds so there's no risk of collision with Xen.
> 
> Maybe "but only on ptes established by ioremap, never on pmds so
> there's no risk of collision with Xen." ? The extra "but" just
> doesn't flow in the original.

Agreed and applied, thanks!
Andrea
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