linux-kernel - Re: [PATCH] mm/filemap: do not allocate cache pages beyond end of file at read

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Message-ID: <CAHk-=who0HS=NT8U7vFDT7er_CD7+ZreRJMxjYrRXs5G6dbpyw@mail.gmail.com>
Date:   Tue, 29 Oct 2019 17:52:05 +0100
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Johannes Weiner <hannes@...xchg.org>,
        Steven Whitehouse <swhiteho@...hat.com>
Subject: Re: [PATCH] mm/filemap: do not allocate cache pages beyond end of
 file at read

On Tue, Oct 29, 2019 at 3:25 PM Konstantin Khlebnikov
<khlebnikov@...dex-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 specially.

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