On Tue, Jun 09, 2015 at 11:00:17PM +0300, Konstantin Khlebnikov wrote:
> From: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
>
> 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 <khlebni...@yandex-team.ru>
> Link:
> http://lkml.kernel.org/r/caevpba+_ryackhodzrrvqls80iy0sqpdrd0aap_-tgnx3y9...@mail.gmail.com
>
> ---
>
> v2:
> * handle transparent huge pages
> * invert bit and rename shared -> exclusive (less confusing name)
> ---
...
> @@ -1119,6 +1122,13 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long
> addr, unsigned long end,
> else
> pmd_flags2 = 0;
>
> + if (pmd_present(*pmd)) {
> + struct page *page = pmd_page(*pmd);
> +
> + if (page_mapcount(page) == 1)
> + pmd_flags2 |= __PM_MMAP_EXCLUSIVE;
> + }
> +
Could you do the same thing for huge_pte_to_pagemap_entry(), too?
Thanks,
Naoya Horiguchi --
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