linux-kernel - Re: [PATCH v3 63/68] nfs: Convert to new fscache volume/cookie API

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Date:   Fri, 17 Dec 2021 08:35:14 -0500
From:   David Wysochanski <dwysocha@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs <linux-cachefs@...hat.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        linux-nfs <linux-nfs@...r.kernel.org>,
        Trond Myklebust <trondmy@...merspace.com>,
        Jeff Layton <jlayton@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 63/68] nfs: Convert to new fscache volume/cookie API

On Fri, Dec 17, 2021 at 8:21 AM David Howells <dhowells@...hat.com> wrote:
>
> David Wysochanski <dwysocha@...hat.com> wrote:
>
> > >
> > >  (4) fscache_enable/disable_cookie() have been removed.
> > >
> > >      Call fscache_use_cookie() and fscache_unuse_cookie() when a file is
> > >      opened or closed to prevent a cache file from being culled and to keep
> > >      resources to hand that are needed to do I/O.
> > >
> > >      Unuse the cookie when a file is opened for writing.  This is gated by
> > >      the NFS_INO_FSCACHE flag on the nfs_inode.
> > >
> > >      A better way might be to invalidate it with FSCACHE_INVAL_DIO_WRITE
> > >      which will keep it unused until all open files are closed.
> > >
> >
> > Comment still out of date here, reference
> > https://marc.info/?l=linux-nfs&m=163922984027745&w=4
>
> Okay, how about:
>
>  (4) fscache_enable/disable_cookie() have been removed.
>
>      Call fscache_use_cookie() and fscache_unuse_cookie() when a file is
>      opened or closed to prevent a cache file from being culled and to keep
>      resources to hand that are needed to do I/O.
>
>      If a file is opened for writing, we invalidate it with
>      FSCACHE_INVAL_DIO_WRITE in lieu of doing writeback to the cache,
>      thereby making it cease caching until all currently open files are
>      closed.  This should give the same behaviour as the uptream code.
>      Making the cache store local modifications isn't straightforward for
>      NFS, so that's left for future patches.
>

Yes, that is more accurate.