Re: [PATCH v4 5/5] pagemap: add mmap-exclusive bit for marking pages mapped only here

[Mark Williamson]

Reviewed-by: Mark Williamson <mwilliamson@xxxxxxxxxxxxxxxxx>

On Tue, Jul 21, 2015 at 9:17 AM, Naoya Horiguchi
<n-horiguchi@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>> Requested-by: Mark Williamson <mwilliamson@xxxxxxxxxxxxxxxxx>
>> Link: http://lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@xxxxxxxxxxxxxx
>
> Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/