Re: [PATCH 4/5] NFSD: Document and rename the NFSv4.1 session slot shrinker callbacks

On Thu, 11 Jun 2026, Chuck Lever wrote:
> Clean up: To prevent their reuse by generic code, rename the NFSv4.1
> session slot shrinker's callback functions to make it clear they are
> for use only by the shrinker.
> 
> Though they are static, callbacks are invoked from outside nfsd.ko,
> so they need appropriate kdoc comments that document their API
> contracts.
> 
> Signed-off-by: Chuck Lever <[email protected]>
> ---
>  fs/nfsd/nfs4state.c | 36 ++++++++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 9735e9a59f0e..7ce8462e3697 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -2196,22 +2196,50 @@ static void free_session(struct nfsd4_session *ses)
>  	__free_session(ses);
>  }
>  
> +/**
> + * nfsd_slot_shrinker_count - report reclaimable DRC slots
> + * @s: shrinker descriptor (unused)
> + * @sc: shrink control (unused)
> + *
> + * Return: a positive count of reclaimable slots, or SHRINK_EMPTY when
> + * there is nothing to reclaim.

I would add to this comment and note that slot zero is not reclaimable,
so that the subtraction of nfsd_total_sessions is explained.

But either way:

Reviewed-by: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>

and you can add that to all patches in series.  A definite improvement!

Thanks,
NeilBrown


> + */
>  static unsigned long
> -nfsd_slot_count(struct shrinker *s, struct shrink_control *sc)
> +nfsd_slot_shrinker_count(struct shrinker *s, struct shrink_control *sc)
>  {
>  	int cnt = atomic_read(&nfsd_total_target_slots) -
>  		  atomic_read(&nfsd_total_sessions);
>  
> +	/*
> +	 * To prevent deadlock, one slot of each session (slot 0) is
> +	 * not reclaimable while the session is active. Thus the
> +	 * number of sessions is subtracted from the total number of
> +	 * target slots.
> +	 */
>  	return cnt > 0 ? cnt : SHRINK_EMPTY;
>  }
>  
> +/**
> + * nfsd_slot_shrinker_scan - reclaim DRC slots under memory pressure
> + * @s: shrinker descriptor (unused)
> + * @sc: shrink control; @sc->nr_to_scan bounds the sessions visited,
> + *      @sc->nr_scanned reports how many were visited
> + *
> + * Return: the number of session slots NFSD will release.
> + */
>  static unsigned long
> -nfsd_slot_scan(struct shrinker *s, struct shrink_control *sc)
> +nfsd_slot_shrinker_scan(struct shrinker *s, struct shrink_control *sc)
>  {
>  	struct nfsd4_session *ses;
>  	unsigned long scanned = 0;
>  	unsigned long freed = 0;
>  
> +	/*
> +	 * Each visited session releases at most one slot. After
> +	 * nr_to_scan sessions have been visited, the list head is
> +	 * rotated past the last visited session so the next scan
> +	 * resumes from there.
> +	 */
>  	spin_lock(&nfsd_session_list_lock);
>  	list_for_each_entry(ses, &nfsd_session_list, se_all_sessions) {
>  		freed += reduce_session_slots(ses, 1);
> @@ -9120,8 +9148,8 @@ nfs4_state_start(void)
>  		rhltable_destroy(&nfs4_file_rhltable);
>  		return -ENOMEM;
>  	}
> -	nfsd_slot_shrinker->count_objects = nfsd_slot_count;
> -	nfsd_slot_shrinker->scan_objects = nfsd_slot_scan;
> +	nfsd_slot_shrinker->count_objects = nfsd_slot_shrinker_count;
> +	nfsd_slot_shrinker->scan_objects = nfsd_slot_shrinker_scan;
>  	shrinker_register(nfsd_slot_shrinker);
>  
>  	set_max_delegations();
> 
> -- 
> 2.54.0
> 
> 
>