linux-kernel - Re: [RFC PATCH 00/53] netfs, afs, cifs: Delegate high-level I/O to netfslib

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Date:   Tue, 17 Oct 2023 11:42:52 +0100
From:   Daire Byrne <daire@...g.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Jeff Layton <jlayton@...nel.org>,
        Steve French <smfrench@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Paulo Alcantara <pc@...guebit.com>,
        Ronnie Sahlberg <lsahlber@...hat.com>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Tom Talpey <tom@...pey.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Christian Brauner <christian@...uner.io>,
        linux-afs@...ts.infradead.org, linux-cifs@...r.kernel.org,
        linux-nfs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/53] netfs, afs, cifs: Delegate high-level I/O to netfslib

On Fri, 13 Oct 2023 at 16:58, David Howells <dhowells@...hat.com> wrote:
>
>  (2) Use of fscache is not yet tested.  I'm not sure whether to allow a
>      cache to be used with a write-through write.

Just adding a quick end user "thumbs up" for this potential feature.
We currently use fscache as the backend for "NFS re-export" servers to
extend our onprem storage to remote cloud compute (which works great).

But batch compute hosts (think VFX render farm) often chunk up stages
of work into multiple batch jobs such that they read data, write
results and then read the same data on different clients. Having the
ability to also cache the recent writes closer to the compute clients
(on the re-export server) would open up a lot of new workload
possibilities for us.

>  (5) Write-through caching will generate and dispatch write subrequests as
>      it gathers enough data to hit wsize and has whole pages that at least
>      span that size.  This needs to be a bit more flexible, allowing for a
>      filesystem such as CIFS to have a variable wsize.

If I understand correctly, this is above and beyond the normal write
back cache and is more in tune with the wsize (of NFS, CIFS etc) for
each file? Again, our workloads are over longer latencies than are
normal (NFS over 200ms!) so this sounds like a nice optimisation when
dealing with slow stuttering file writes over high latency.

I can definitely volunteer for some of the fscache + NFS testing.

Cheers,

Daire