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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 13 Jan 2021 11:54:44 -0800
Message-ID: <CAHk-=wh=-_F1_ozuF6Wzg1-u07iLuUG_77SQeuX7gwgC5DQKzQ@mail.gmail.com>
Subject: Re: [PATCH 0/1] mm: restore full accuracy in COW page reuse
To:     Matthew Wilcox <willy@infradead.org>
Cc:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        John Hubbard <jhubbard@nvidia.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Yu Zhao <yuzhao@google.com>, Andy Lutomirski <luto@kernel.org>,
        Peter Xu <peterx@redhat.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Minchan Kim <minchan@kernel.org>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Hugh Dickins <hughd@google.com>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Leon Romanovsky <leonro@nvidia.com>,
        Jason Gunthorpe <jgg@ziepe.ca>, Jan Kara <jack@suse.cz>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Nadav Amit <nadav.amit@gmail.com>, Jens Axboe <axboe@kernel.dk>
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On Wed, Jan 13, 2021 at 4:56 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> Yes, Linus mis-stated it:

Yeah, I got the order wrong.

> ... but as David pointed out, I fixed this in e320d3012d25

.. and I must have seen it, but not really internalized it.

And now that I look at it more closely, I'm actually surprised that
other than the magic "speculative first page" case we don't seem to
use page reference counting for non-order-0 pages (which would break
that hack horribly).

             Linus