Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 22 Apr 2021 17:18:47 -0400
From:   Peter Xu <peterx@redhat.com>
To:     Axel Rasmussen <axelrasmussen@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Joe Perches <joe@perches.com>,
        Lokesh Gidra <lokeshgidra@google.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Shaohua Li <shli@fb.com>, Shuah Khan <shuah@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Wang Qing <wangqing@vivo.com>, linux-api@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        linux-kselftest@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
        Brian Geffon <bgeffon@google.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Mina Almasry <almasrymina@google.com>,
        Oliver Upton <oupton@google.com>
Subject: Re: [PATCH v4 03/10] userfaultfd/shmem: support UFFDIO_CONTINUE for
 shmem
Message-ID: <20210422211847.GF6404@xz-x1>
References: <20210420220804.486803-1-axelrasmussen@google.com>
 <20210420220804.486803-4-axelrasmussen@google.com>
 <CAJHvVchQk1zrgah08n_P3sHUVzQLZUXHSMbkpd9rG-w5jUGNdw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAJHvVchQk1zrgah08n_P3sHUVzQLZUXHSMbkpd9rG-w5jUGNdw@mail.gmail.com>
Precedence: bulk

Axel,

On Thu, Apr 22, 2021 at 01:22:02PM -0700, Axel Rasmussen wrote:
> > +       if (page_in_cache)
> > +               page_add_file_rmap(page, false);
> > +       else
> > +               page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
> > +
> > +       /*
> > +        * Must happen after rmap, as mm_counter() checks mapping (via
> > +        * PageAnon()), which is set by __page_set_anon_rmap().
> > +        */
> > +       inc_mm_counter(dst_mm, mm_counter(page));
> 
> Actually, I've noticed that this is still slightly incorrect.
> 
> As Hugh pointed out, this works for the anon case, because
> page_add_new_anon_rmap() sets page->mapping.
> 
> But for the page_in_cache case, it doesn't work: unlike its anon
> counterpart, page_add_file_rmap() *does not* set page->mapping.

If it's already in the page cache, shouldn't it be set already in e.g. one
previous call to shmem_add_to_page_cache()?  Thanks,

-- 
Peter Xu