Re: [RFC] Optional FUSE flush-on-close

[Miklos Szeredi <miklos@szeredi.hu>]

On Tue, 19 Oct 2021 at 18:12, Amir Goldstein <amir73il@gmail.com> wrote:
>
> Miklos,
>
> We have a use case where fuse_sync_writes() is disruptive
> to the workload.
>
> Some applications, which are not under our control do
> open(O_RDONLY);fstat();close() and are made to block waiting on writes
> that they are not responsible for.
>
> Looking at other network filesystems, cifs and nfs only flush on close
> for FMODE_WRITE files.
> Some older SMB flavors (smb1, smb2) do also flush on RDONLY files.
>
> In particular, our FUSE filesystem does not even implement FLUSH
> and it has writeback caching disabled, so the value of flush on close
> is even more questionable.
>
> Would you be willing to consider a patch that makes flush-on-close
> behavior optional for RDONLY files?
> If so, should I make this option available only when filesystem
> does not implement FLUSH or independent?
> Should I make an option to completely disable flush-on-close
> (i.e. like most disk filesystems)?

Flushing dirty pages for writable files  is mandatory for the
writeback cache case.  Otherwise you are correct, this could be
disabled.

How about FOPEN_NOFLUSH?

Thanks,
Miklos

>
> Thanks,
> Amir.