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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Jeff Layton <jlayton@kernel.org>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH] nfsd: queue laundrette to filecache_wq instead of
 system_wq
Thread-Topic: [PATCH] nfsd: queue laundrette to filecache_wq instead of
 system_wq
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Date:   Mon, 7 Nov 2022 15:56:58 +0000
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> On Nov 7, 2022, at 10:55 AM, Jeff Layton <jlayton@kernel.org> wrote:
>=20
> 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
>=20
> Good question.
>=20
> At one time, allocating a workqueue gave you a dedicated pool of
> threads, but that's no longer the case.
>=20
> 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."
>=20
> 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.

One less thing to fail on module initialization. Go for it.


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

--
Chuck Lever