Re: Mapcount of subpages

From: Kirill A. Shutemov
Date: Fri Sep 24 2021 - 19:05:12 EST

On Thu, Sep 23, 2021 at 02:10:13PM -0700, Hugh Dickins wrote:
> But you have a different point in mind when you refer to superfluous
> CoW and GUP: I don't know the score there (and I think we are still in
> that halfway zone, since pte CoW was changed to depend on page_count,
> but THP CoW still depending on mapcount).

I didn't pay enough attention to the topic when the change to depend on
page_count was made. I need to catch up.

I look at what direction Andrea went in his patchset and so far I *feel*
he has a point[1]. I have not read the whole thing yet and I don't have a
firm position here, but maybe we need to get to the bottom of the topic
before considering ditching per-subpage mapcount.


Kirill A. Shutemov