linux-kernel - Re: [PATCH 1/2] mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps

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Date:   Mon, 13 Feb 2023 17:40:05 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        James Houghton <jthoughton@...gle.com>,
        Peter Xu <peterx@...hat.com>, Yang Shi <shy828301@...il.com>,
        Vishal Moola <vishal.moola@...il.com>,
        Muchun Song <songmuchun@...edance.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: hugetlb: proc: check for hugetlb shared PMD in
 /proc/PID/smaps

On 02/13/23 19:01, Michal Hocko wrote:
> On Fri 03-02-23 12:16:04, Mike Kravetz wrote:
> [...]
> > Unless someone thinks we should move forward, I will not push the code
> > for this approach now.  It will also be interesting to see if this is
> > impacted at all by the outcome of discussions to perhaps redesign
> > mapcount.
> 
> Yes, I do agree. We might want to extend page_mapcount documentation a
> bit though. The comment is explicit about the order-0 pages but a note
> about hugetlb and pmd sharing wouldn't hurt. WDYT?

Looks like that comment about 'Mapcount of 0-order page' has been removed in
the latest version of page_mapcount().  It would not surprise me if the calls
to page_mapcount after which we check for shared PMDs will soon be replaced
with calls to folio_mapcount().

Perhaps Matthew has an opinion as to where map counts for hugetlb shared
PMDs might be mentioned.
-- 
Mike Kravetz