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Subject: Re: [PATCH] mm/filemap: do not allocate cache pages beyond end of
 file at read
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Linux-MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "cluster-devel@redhat.com" <cluster-devel@redhat.com>
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From:   Steven Whitehouse <swhiteho@redhat.com>
Message-ID: <f0140b13-cca2-af9e-eb4b-82eda134eb8f@redhat.com>
Date:   Wed, 30 Oct 2019 10:34:22 +0000
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Hi,

On 29/10/2019 16:52, Linus Torvalds wrote:
> On Tue, Oct 29, 2019 at 3:25 PM Konstantin Khlebnikov
> <khlebnikov@yandex-team.ru> wrote:
>> I think all network filesystems which synchronize metadata lazily should=
 be
>> marked. For example as "SB_VOLATILE". And vfs could handle them speciall=
y.
> No need. The VFS layer doesn't call generic_file_buffered_read()
> directly anyway. It's just a helper function for filesystems to use if
> they want to.
>
> They could (and should) make sure the inode size is sufficiently
> up-to-date before calling it. And if they want something more
> synchronous, they can do it themselves.
>
> But NFS, for example, has open/close consistency, so the metadata
> revalidation is at open() time, not at read time.
>
>                 Linus

NFS may be ok here, but it will break GFS2. There may be others too...=20
OCFS2 is likely one. Not sure about CIFS either. Does it really matter=20
that we might occasionally allocate a page and then free it again?

Ramfs is a simple test case, but at the same time it doesn't represent=20
the complexity of a real world filesystem. I'm just back from a few days=20
holiday so apologies if I've missed something earlier on in the discussions=
,

Steve.