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Subject: Re: [PATCH] nfsd: queue laundrette to filecache_wq instead of
 system_wq
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Date:   Mon, 07 Nov 2022 10:55:04 -0500
In-Reply-To: <2FC9BEB2-189B-4EF6-AC61-40263BC47737@oracle.com>
References: <20221107150128.46951-1-jlayton@kernel.org>
         <2FC9BEB2-189B-4EF6-AC61-40263BC47737@oracle.com>
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On Mon, 2022-11-07 at 15:11 +0000, Chuck Lever III wrote:
> Hi Jeff -
>=20
> > On Nov 7, 2022, at 10:01 AM, Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > nfsd has grown a dedicated workqueue for the filecache, but this job is
> > still queued to the system_wq. Change it to use the filecache_wq.
>=20
> Actually... there doesn't seem to be anything special about
> nfsd_filecache_wq. 9542e6a643fc ("nfsd: Containerise filecache
> laundrette") does not make clear why it was added.
>=20
> Playing devil's advocate: why not make the converse change and
> replace it with system_wq?
>=20

Good question.

At one time, allocating a workqueue gave you a dedicated pool of
threads, but that's no longer the case.

Documentation/core-api/workqueue.rst says: "A wq no longer manages
execution resources but serves as a domain for forward progress
guarantee, flush and work item attributes."

Given that we're allocating this workqueue exactly the same way we
allocate the system_wq, I don't think we need our own workqueue at all.
I'd be fine with changing this to be the reverse if you prefer.

>=20
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/nfsd/filecache.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >=20
> > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> > index 1e76b0d3b83a..018fd1565193 100644
> > --- a/fs/nfsd/filecache.c
> > +++ b/fs/nfsd/filecache.c
> > @@ -212,7 +212,7 @@ static void
> > nfsd_file_schedule_laundrette(void)
> > {
> > 	if (test_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags))
> > -		queue_delayed_work(system_wq, &nfsd_filecache_laundrette,
> > +		queue_delayed_work(nfsd_filecache_wq, &nfsd_filecache_laundrette,
> > 				   NFSD_LAUNDRETTE_DELAY);
> > }
> >=20
> > --=20
> > 2.38.1
> >=20
>=20
> --
> Chuck Lever
>=20
>=20
>=20

--=20
Jeff Layton <jlayton@kernel.org>