Re: [PATCH v2 35/47] nfsd: dynamically allocate the nfsd-reply shrinker

[Jeff Layton <jlayton@xxxxxxxxxx>]

On Mon, 2023-07-24 at 17:43 +0800, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the nfsd-reply shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct nfsd_net.
> 
> Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> ---
>  fs/nfsd/netns.h    |  2 +-
>  fs/nfsd/nfscache.c | 31 ++++++++++++++++---------------
>  2 files changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index f669444d5336..ab303a8b77d5 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -177,7 +177,7 @@ struct nfsd_net {
>       /* size of cache when we saw the longest hash chain */
>       unsigned int             longest_chain_cachesize;
>  
> -     struct shrinker         nfsd_reply_cache_shrinker;
> +     struct shrinker         *nfsd_reply_cache_shrinker;
>  
>       /* tracking server-to-server copy mounts */
>       spinlock_t              nfsd_ssc_lock;
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 6eb3d7bdfaf3..9f0ab65e4125 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -200,26 +200,29 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
>  {
>       unsigned int hashsize;
>       unsigned int i;
> -     int status = 0;
>  
>       nn->max_drc_entries = nfsd_cache_size_limit();
>       atomic_set(&nn->num_drc_entries, 0);
>       hashsize = nfsd_hashsize(nn->max_drc_entries);
>       nn->maskbits = ilog2(hashsize);
>  
> -     nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
> -     nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
> -     nn->nfsd_reply_cache_shrinker.seeks = 1;
> -     status = register_shrinker(&nn->nfsd_reply_cache_shrinker,
> -                                "nfsd-reply:%s", nn->nfsd_name);
> -     if (status)
> -             return status;
> -
>       nn->drc_hashtbl = kvzalloc(array_size(hashsize,
>                               sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
>       if (!nn->drc_hashtbl)
> +             return -ENOMEM;
> +
> +     nn->nfsd_reply_cache_shrinker = shrinker_alloc(0, "nfsd-reply:%s",
> +                                                    nn->nfsd_name);
> +     if (!nn->nfsd_reply_cache_shrinker)
>               goto out_shrinker;
>  
> +     nn->nfsd_reply_cache_shrinker->scan_objects = nfsd_reply_cache_scan;
> +     nn->nfsd_reply_cache_shrinker->count_objects = nfsd_reply_cache_count;
> +     nn->nfsd_reply_cache_shrinker->seeks = 1;
> +     nn->nfsd_reply_cache_shrinker->private_data = nn;
> +
> +     shrinker_register(nn->nfsd_reply_cache_shrinker);
> +
>       for (i = 0; i < hashsize; i++) {
>               INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
>               spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
> @@ -228,7 +231,7 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
>  
>       return 0;
>  out_shrinker:
> -     unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
> +     kvfree(nn->drc_hashtbl);
>       printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
>       return -ENOMEM;
>  }
> @@ -238,7 +241,7 @@ void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
>       struct nfsd_cacherep *rp;
>       unsigned int i;
>  
> -     unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
> +     shrinker_unregister(nn->nfsd_reply_cache_shrinker);
>  
>       for (i = 0; i < nn->drc_hashsize; i++) {
>               struct list_head *head = &nn->drc_hashtbl[i].lru_head;
> @@ -322,8 +325,7 @@ nfsd_prune_bucket_locked(struct nfsd_net *nn, struct 
> nfsd_drc_bucket *b,
>  static unsigned long
>  nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
>  {
> -     struct nfsd_net *nn = container_of(shrink,
> -                             struct nfsd_net, nfsd_reply_cache_shrinker);
> +     struct nfsd_net *nn = shrink->private_data;
>  
>       return atomic_read(&nn->num_drc_entries);
>  }
> @@ -342,8 +344,7 @@ nfsd_reply_cache_count(struct shrinker *shrink, struct 
> shrink_control *sc)
>  static unsigned long
>  nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
>  {
> -     struct nfsd_net *nn = container_of(shrink,
> -                             struct nfsd_net, nfsd_reply_cache_shrinker);
> +     struct nfsd_net *nn = shrink->private_data;
>       unsigned long freed = 0;
>       LIST_HEAD(dispose);
>       unsigned int i;

Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>