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Date: Tue, 7 Oct 2014 14:10:26 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
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Subject: Re: [Qemu-devel] [PATCH 10/17] mm: rmap preparation for
 remap_anon_pages
Message-ID: <20141007111026.GD30762@node.dhcp.inet.fi>
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On Fri, Oct 03, 2014 at 07:08:00PM +0200, Andrea Arcangeli wrote:
> There's one constraint enforced to allow this simplification: the
> source pages passed to remap_anon_pages must be mapped only in one
> vma, but this is not a limitation when used to handle userland page
> faults with MADV_USERFAULT. The source addresses passed to
> remap_anon_pages should be set as VM_DONTCOPY with MADV_DONTFORK to
> avoid any risk of the mapcount of the pages increasing, if fork runs
> in parallel in another thread, before or while remap_anon_pages runs.

Have you considered triggering COW instead of adding limitation on
pages' mapcount? The limitation looks artificial from interface POV.

-- 
 Kirill A. Shutemov