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Date: Wed, 01 Oct 2014 13:29:04 -0400
From: Rik van Riel <riel@redhat.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>
CC: Dave Jones <davej@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Michel Lespinasse <walken@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, Sasha Levin <sasha.levin@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: pipe/page fault oddness.
References: <20140930033327.GA14558@redhat.com>	<CA+55aFwmo7ot=h7tpUYhSC49CHKBK2KfGaDJ_fwB0=VNqvTPBQ@mail.gmail.com>	<20140930043309.GA16196@redhat.com>	<CA+55aFwxdOBKHwwp7Zq1k19mHCyHYmYqigCVt59AtB-P7Zva1w@mail.gmail.com>	<CA+55aFynr-Abo_JY1=GGOf9e2tjJvexbX2kVTgD0bkq7BXacJw@mail.gmail.com>	<20140930160510.GA15903@redhat.com>	<CA+55aFzTEXxxh_4_BwVydw1UgCu-NRF95OrzVhj=cievXFTJTg@mail.gmail.com>	<20140930162201.GC15903@redhat.com>	<20140930164047.GA18354@redhat.com>	<CA+55aFzKgJ41Mp=Ub8Kq_uFDHYzkHo3zhO3MHOJo_O2iExdYmQ@mail.gmail.com>	<20140930182059.GA24431@redhat.com>	<CA+55aFzfvXHd2LUhQ5OiV1H1Oq2y3PL8hX_Hrv-C907PyDNugA@mail.gmail.com>	<alpine.LSU.2.11.1410010031070.1902@eggly.anvils>	<CA+55aFyJ09+iv2HX1nfAaDi0-7=L3KxKi11CACbM8K_Coo6kzg@mail.gmail.com> <CA+55aFzHgemAV7igyG=0pmctTaV7cZfO4fdqukhrCc8VXTrZuw@mail.gmail.com>
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On 10/01/2014 12:18 PM, Linus Torvalds wrote:

> Seriously, why can't we just do this, and throw away all the crap that
> is "numa special case". This would make all the random games in
> change_pte_range() just go away entirely, because the whole NUMA thing
> really wouldn't be a special case for the pte AT ALL any more. All it
> would be is that a pte could be marked PROT_NONE even if the
> vma->vm_flags aren't.

That's what I suggested quite a while back, but IIRC either
Peter or Mel brought up a reason why this was not possible.

Unfortunately I do not remember what it was, just that I
was convinced by it at the time...