Re: [PATCH v3 2/2] NFSD: add counter for write delegation recall due to conflict with GETATTR

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2023-05-30 at 19:35 -0700, Dai Ngo wrote:
> Add counter to keep track of how many times write delegations are
> recalled due to conflict with GETATTR.
> 
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 1 +
>  fs/nfsd/stats.c     | 2 ++
>  fs/nfsd/stats.h     | 7 +++++++
>  3 files changed, 10 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 29ed2e72b665..cba27dfa39e8 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -8402,6 +8402,7 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct inode *inode)
>  			}
>  break_lease:
>  			spin_unlock(&ctx->flc_lock);
> +			nfsd_stats_wdeleg_getattr_inc();
>  			status = nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));
>  			if (status != nfserr_jukebox ||
>  					!nfsd_wait_for_delegreturn(rqstp, inode))
> diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
> index 777e24e5da33..63797635e1c3 100644
> --- a/fs/nfsd/stats.c
> +++ b/fs/nfsd/stats.c
> @@ -65,6 +65,8 @@ static int nfsd_show(struct seq_file *seq, void *v)
>  		seq_printf(seq, " %lld",
>  			   percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_NFS4_OP(i)]));
>  	}
> +	seq_printf(seq, "\nwdeleg_getattr %lld",
> +		percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_WDELEG_GETATTR]));
>  
>  	seq_putc(seq, '\n');
>  #endif
> diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
> index 9b43dc3d9991..cf5524e7ca06 100644
> --- a/fs/nfsd/stats.h
> +++ b/fs/nfsd/stats.h
> @@ -22,6 +22,7 @@ enum {
>  	NFSD_STATS_FIRST_NFS4_OP,	/* count of individual nfsv4 operations */
>  	NFSD_STATS_LAST_NFS4_OP = NFSD_STATS_FIRST_NFS4_OP + LAST_NFS4_OP,
>  #define NFSD_STATS_NFS4_OP(op)	(NFSD_STATS_FIRST_NFS4_OP + (op))
> +	NFSD_STATS_WDELEG_GETATTR,	/* count of getattr conflict with wdeleg */
>  #endif
>  	NFSD_STATS_COUNTERS_NUM
>  };
> @@ -93,4 +94,10 @@ static inline void nfsd_stats_drc_mem_usage_sub(struct nfsd_net *nn, s64 amount)
>  	percpu_counter_sub(&nn->counter[NFSD_NET_DRC_MEM_USAGE], amount);
>  }
>  
> +#ifdef CONFIG_NFSD_V4
> +static inline void nfsd_stats_wdeleg_getattr_inc(void)
> +{
> +	percpu_counter_inc(&nfsdstats.counter[NFSD_STATS_WDELEG_GETATTR]);
> +}
> +#endif
>  #endif /* _NFSD_STATS_H */

Personally, I think it would still be simpler to just do a CB_GETATTR.
We are issuing a callback in either case, but recalling the delegation
seems like a less optimal outcome.

Still for an interim step, this is fine...

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