Re: [Qemu-devel] [PATCH 10/17] mm: rmap preparation for remap_anon_pages

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

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