On Sun, 2023-07-09 at 11:45 -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> To reduce contention on the bucket locks, we must avoid calling
> kfree() while each bucket lock is held.
>
> Start by refactoring nfsd_reply_cache_free_locked() into a helper
> that removes an entry from the bucket (and must therefore run under
> the lock) and a second helper that frees the entry (which does not
> need to hold the lock).
>
> For readability, rename the helpers nfsd_cacherep_<verb>.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/nfscache.c | 26 +++++++++++++++++++-------
> 1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index a8eda1c85829..601298b7f75f 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -110,21 +110,32 @@ nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum,
> return rp;
> }
>
> +static void nfsd_cacherep_free(struct svc_cacherep *rp)
> +{
> + kfree(rp->c_replvec.iov_base);
> + kmem_cache_free(drc_slab, rp);
> +}
> +
> static void
> -nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
> - struct nfsd_net *nn)
> +nfsd_cacherep_unlink_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
> + struct svc_cacherep *rp)
> {
> - if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
> + if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base)
> nfsd_stats_drc_mem_usage_sub(nn, rp->c_replvec.iov_len);
> - kfree(rp->c_replvec.iov_base);
> - }
> if (rp->c_state != RC_UNUSED) {
> rb_erase(&rp->c_node, &b->rb_head);
> list_del(&rp->c_lru);
> atomic_dec(&nn->num_drc_entries);
> nfsd_stats_drc_mem_usage_sub(nn, sizeof(*rp));
> }
> - kmem_cache_free(drc_slab, rp);
> +}
> +
> +static void
> +nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
> + struct nfsd_net *nn)
> +{
> + nfsd_cacherep_unlink_locked(nn, b, rp);
> + nfsd_cacherep_free(rp);
> }
>
> static void
> @@ -132,8 +143,9 @@ nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
> struct nfsd_net *nn)
> {
> spin_lock(&b->cache_lock);
> - nfsd_reply_cache_free_locked(b, rp, nn);
> + nfsd_cacherep_unlink_locked(nn, b, rp);
> spin_unlock(&b->cache_lock);
> + nfsd_cacherep_free(rp);
> }
>
> int nfsd_drc_slab_create(void)
>
>
Seems straightforward. I do question whether this will make any
different for performance, but it's unlikely to hurt anything, and it's
nice to separate the "unlink" and "free" functions.
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
