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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 12 Jan 2021 18:43:17 -0800
Message-ID: <CAHk-=whxDS7DHHN=ZHCUskXu3A2h3Z5F427kTJqvc5P_8x8ecw@mail.gmail.com>
Subject: Re: [PATCH 0/1] mm: restore full accuracy in COW page reuse
To:     Matthew Wilcox <willy@infradead.org>
Cc:     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>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        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 Tue, Jan 12, 2021 at 6:16 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> The thing about the speculative page cache references is that they can
> temporarily bump a refcount on a page which _used_ to be in the page
> cache and has now been reallocated as some other kind of page.

Right you are. Yeah, scratch the "we could make it absolute on 1", and
we do need the PIN count elevation.

           Linus