Messages in this thread | | | From | Naoya Horiguchi <> | Subject | Re: [PATCH v4 5/5] pagemap: add mmap-exclusive bit for marking pages mapped only here | Date | Tue, 21 Jul 2015 08:17:56 +0000 |
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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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