Re: [PATCH] mm: Save soft-dirty bits on swapped pages

[Andy Lutomirski]

On Thu, Jul 25, 2013 at 12:29 AM, Pavel Emelyanov <xemul@xxxxxxxxxxxxx> wrote:
> On 07/24/2013 11:40 PM, Andy Lutomirski wrote:
>> On Wed, Jul 24, 2013 at 12:04 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:
>>> On Wed, Jul 24, 2013 at 10:55:41PM +0400, Pavel Emelyanov wrote:
>>>>>
>
>> Perhaps another bit should be allocated to expose to userspace either
>> "soft-dirty", "soft-clean", or "soft-dirty unsupported"?
>>
>> There's another possible issue with private file-backed pages, though:
>> how do you distinguish clean-and-not-cowed from cowed-but-soft-clean?
>> (The former will reflect changes in the underlying file, I think, but
>> the latter won't.)
>
> There's a bit called PAGE_FILE bit in /proc/pagemap file introduced with
> the 052fb0d635df5d49dfc85687d94e1a87bf09378d commit.
>
> Plz, refer to Documentation/vm/pagemap.txt and soft-dirty.txt, all this
> is described there pretty well.
>

Fair enough.  I'm still a little bit concerned that it will be hard
for userspace to distinguish between things for which soft-dirty works
(which will be more things once the patches are in) and things for
which soft-dirty doesn't work, assuming any are left.  But maybe this
is silly.

--Andy
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