Re: [PATCH v3 0/8] NFSD: CB_RECALL_ANY fixes and a meaningful keep count

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2026-08-13 at 14:40 -0400, Chuck Lever wrote:
> NFSD currently sends every CB_RECALL_ANY with craa_objects_to_keep
> set to zero, as RFC 8881 Section 20.6.3 does not mandate any
> particular way for a client to choose which delegations to return,
> if any.
> 
> NFSD intends CB_RECALL_ANY only as a signal to return currently
> unused delegations. To date, only the Linux NFS client has been
> deeply tested against it. That implementation ignores the
> craa_objects_to_keep value and returns only one unused delegation
> of the named types. Therefore the fixed zero craa_objects_to_keep
> value never produced visible misbehavior during our testing.
> 
> However, a zero value can result in non-Linux clients giving back
> more delegations than is necessary to relieve temporary memory
> pressure on the server, which needlessly punctures the clients'
> delegation working set.
> 
> Change NFSD so that each CB_RECALL_ANY asks a client to give up a
> sensible number of delegations instead of all of them at once. To
> handle the accounting correctly, it is necessary for this series to
> split the current state shrinker mechanism. The patch descriptions
> have those details.
> 
> ---
> Changes in v3:
> - Count delegations per namespace so each shrinker reports its own.
> - Give courtesy clients and delegations separate state shrinkers.
> - Record the shrinker's scan requests and discount the count by them.
> - Scale each client's CB_RECALL_ANY by its share of the scan request.
> - Reword the keep-count rationale in the commit message and comment.
> - Link to v2: https://patch.msgid.link/20260812-recall-any-keep-count-v2-0-a82f4ca23812@kernel.org
> 
> Changes in v2:
> - Drop the gate that skipped clients holding a single delegation.
> - Cover letter rewritten to give performance rationale.
> - Link to v1: https://patch.msgid.link/20260811-recall-any-keep-count-v1-0-de9ca00493b7@kernel.org
> 
> ---
> Chuck Lever (8):
>       NFSD: Do not send CB_RECALL_ANY to NFSv4.0 clients
>       NFSD: Count the delegations held by each client
>       NFSD: Name directory delegations in the CB_RECALL_ANY type mask
>       NFSD: Send a meaningful CB_RECALL_ANY keep count
>       NFSD: Count delegations per network namespace
>       NFSD: Give delegations their own state shrinker
>       NFSD: Pace the state shrinker's scan requests
>       NFSD: Apportion CB_RECALL_ANY recalls among clients
> 
>  fs/nfsd/netns.h     |  17 +++-
>  fs/nfsd/nfs4state.c | 235 +++++++++++++++++++++++++++++++++++++++++++++-------
>  fs/nfsd/state.h     |   2 +
>  3 files changed, 223 insertions(+), 31 deletions(-)
> ---
> base-commit: 1d479c6b53f684b27da84ec352b7efb97f7f115f
> change-id: 20260810-recall-any-keep-count-f50c2ae1b792
> 
> Best regards,
> --  
> Chuck Lever <cel@kernel.org>

You can add this to 5-8:

Reviewed-by: Jeff Layton <jlayton@kernel.org>