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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 18 Nov 2022 12:18:42 -0800
Message-ID: <CAHk-=whmq5gHrKmD3j=7nB=n9OmmLb5j1qmoQPHw1=VSQ-V=hg@mail.gmail.com>
Subject: Re: [PATCH 0/3] mm,thp,rmap: rework the use of subpages_mapcount
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>, Peter Xu <peterx@redhat.com>,
        Yang Shi <shy828301@gmail.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Sidhartha Kumar <sidhartha.kumar@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Mina Almasry <almasrymina@google.com>,
        James Houghton <jthoughton@google.com>,
        "Zach O'Keefe" <zokeefe@google.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
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On Fri, Nov 18, 2022 at 1:08 AM Hugh Dickins <hughd@google.com> wrote:
>
> Linus was underwhelmed by the earlier compound mapcounts series:
> this series builds on top of it (as in next-20221117) to follow
> up on his suggestions - except rmap.c still using lock_page_memcg(),
> since I hesitate to steal the pleasure of deletion from Johannes.

This looks good to me. Particularly 2/3 made me go "Aww, yes" but the
overall line removal stats look good too.

That said, I only looked at the patches, and not the end result
itself. But not having the bit spin lock is, I think, a huge
improvement.

I do wonder if this should be now just merged with your previous
series - it looks a bit odd how your previous series adds that
bitlock, only for it to be immediately removed.

But if you think the logic ends up being easier to follow this way as
two separate patch series, I guess I don't care.

And the memcg locking is entirely a separate issue, and I hope
Johannes will deal with that.

Thanks,
              Linus