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SubjectRe: [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages mapped only here
On 12.05.2015 13:40, Kirill A. Shutemov wrote:
> On Tue, May 12, 2015 at 12:43:03PM +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)
>
> Probably, worth noting that file-private pages are anon in this context.
>

You mean there's another kind of CoW pages? Yep, but from the kernel
point of view these pages are the same. Anyway Userspace could look
into /proc/*/maps and see is there any file beyond anon vma.

--
Konstantin


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