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Date:   Thu, 10 Aug 2023 04:25:59 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Peter Xu <peterx@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-doc@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Hugh Dickins <hughd@google.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        Yin Fengwei <fengwei.yin@intel.com>,
        Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>
Subject: Re: [PATCH mm-unstable v1] mm: add a total mapcount for large folios
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References: <20230809083256.699513-1-david@redhat.com>
 <ZNQD4pxo8svpGmvX@x1n>
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On Wed, Aug 09, 2023 at 05:23:46PM -0400, Peter Xu wrote:
> Hi, David,
> 
> Some pure questions below..
> 
> On Wed, Aug 09, 2023 at 10:32:56AM +0200, David Hildenbrand wrote:
> > Let's track the total mapcount for all large folios in the first subpage.
> > 
> > The total mapcount is what we actually want to know in folio_mapcount()
> > and it is also sufficient for implementing folio_mapped(). This also
> > gets rid of any "raceiness" concerns as expressed in
> > folio_total_mapcount().
> 
> Any more information for that "raciness" described here?

UTSL.

        /*
         * Add all the PTE mappings of those pages mapped by PTE.
         * Limit the loop to folio_nr_pages_mapped()?
         * Perhaps: given all the raciness, that may be a good or a bad idea.
         */