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SubjectRe: [PATCH v4 5/5] pagemap: add mmap-exclusive bit for marking pages mapped only here
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Reviewed-by: Mark Williamson <mwilliamson@undo-software.com>

On Tue, Jul 21, 2015 at 9:17 AM, Naoya Horiguchi
<n-horiguchi@ah.jp.nec.com> wrote:
> On Tue, Jul 14, 2015 at 06:37:49PM +0300, Konstantin Khlebnikov wrote:
>> This patch sets bit 56 in pagemap if this page is mapped only once.
>> It allows to detect exclusively used pages without exposing PFN:
>>
>> present file exclusive state
>> 0 0 0 non-present
>> 1 1 0 file page mapped somewhere else
>> 1 1 1 file page mapped only here
>> 1 0 0 anon non-CoWed page (shared with parent/child)
>> 1 0 1 anon CoWed page (or never forked)
>>
>> CoWed pages in (MAP_FILE | MAP_PRIVATE) areas are anon in this context.
>>
>> MMap-exclusive bit doesn't reflect potential page-sharing via swapcache:
>> page could be mapped once but has several swap-ptes which point to it.
>> Application could detect that by swap bit in pagemap entry and touch
>> that pte via /proc/pid/mem to get real information.
>>
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>> Requested-by: Mark Williamson <mwilliamson@undo-software.com>
>> Link: http://lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@mail.gmail.com
>
> Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>


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