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From:   David Howells <dhowells@redhat.com>
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To:     Steve French <smfrench@gmail.com>
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Subject: Re: [PATCH 00/67] fscache: Rewrite index API and management system
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Date:   Fri, 22 Oct 2021 19:52:18 +0100
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Steve French <smfrench@gmail.com> wrote:

> On Thu, Oct 21, 2021 at 5:21 PM Omar Sandoval <osandov@osandov.com> wrot=
e:
> >
> > On Mon, Oct 18, 2021 at 03:50:15PM +0100, David Howells wrote:
> > However, with the advent of the tmpfile capacity in the VFS, an opport=
unity
> > arises to do invalidation much more easily, without having to wait for=
 I/O
> > that's actually in progress: Cachefiles can simply cut over its file
> > pointer for the backing object attached to a cookie and abandon the
> > in-progress I/O, dismissing it upon completion.
> =

> Have changes been made to O_TMPFILE?  It is problematic for network
> filesystems because it is not an atomic operation, and would be great if=
 it
> were possible to create a tmpfile and open it atomically (at the file sy=
stem
> level).

In this case, it's nothing to do with the network filesystem that's using =
the
cache per se.  Cachefiles is using tmpfiles on the backing filesystem, so =
as
long as that's, say, ext4, xfs or btrfs, it should work fine.  The backing
filesystem also needs to support SEEK_HOLE and SEEK_DATA.

I'm not sure I'd recommend putting your cache on a network filesystem.

David