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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Tom Talpey <tom@talpey.com>, Dai Ngo <dai.ngo@oracle.com>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 1/2] NFSD: add support for sending CB_RECALL_ANY
Thread-Topic: [PATCH 1/2] NFSD: add support for sending CB_RECALL_ANY
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Date:   Tue, 18 Oct 2022 14:03:51 +0000
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> On Oct 18, 2022, at 9:25 AM, Tom Talpey <tom@talpey.com> wrote:
>=20
> On 10/18/2022 1:15 AM, Dai Ngo wrote:
>> There is only one nfsd4_callback, cl_recall_any, added for each
>> nfs4_client. Access to it must be serialized. For now it's done
>> by the cl_recall_any_busy flag since it's used only by the
>> delegation shrinker. If there is another consumer of CB_RECALL_ANY
>> then a spinlock must be used.
>=20
> I'm curious if clients have shown any quirks with the operation in
> your testing. If the (Linux) server hasn't ever been sending it,
> then I'd expect some possible issues/quirks in the client.

Is Linux NFSD the first implementation of CB_RECALL_ANY? If other
servers already have this capability, I would expect clients to
work adequately.

Of course, if the community doesn't have any unit tests for
CB_RECALL_ANY... "what's not tested is broken" -- Brian Wong.


> For example, do they really start handing back a significant number
> of useful delegations? Enough to satisfy the server's need without
> going to specific resource-based recalls?

I don't think of CB_RECALL_ANY as heroic, it's more of a hint. So
if a client doesn't return anything, that's not really a problem --
NFSD is not relying on it, and it certainly does take some time
before server-side state resources are eventually released.

Another possible use case is for the server to start sending
CB_RECALL_ANY when a client hits the max per-client delegation
limit.


--
Chuck Lever