Re: [PATCH 15/15] knfsd: Improve lookup performance in the duplicate reply cache using an rbtree

["J . Bruce Fields" <bfields@fieldses.org>]

On Mon, Oct 01, 2018 at 10:41:57AM -0400, Trond Myklebust wrote:
> Use an rbtree to ensure the lookup/insert of an entry in a DRC bucket is
> O(log(N)).

So the naming on those hash chain statistics are off now, but I guess
that's harmless.

All looks good to me, thanks--applying.

--b.

> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  fs/nfsd/cache.h    |  1 +
>  fs/nfsd/nfscache.c | 37 ++++++++++++++++++++++++++-----------
>  2 files changed, 27 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
> index cbcdc15753b7..ef1c8aa89ca4 100644
> --- a/fs/nfsd/cache.h
> +++ b/fs/nfsd/cache.h
> @@ -29,6 +29,7 @@ struct svc_cacherep {
>  		struct sockaddr_in6	k_addr;
>  	} c_key;
>  
> +	struct rb_node		c_node;
>  	struct list_head	c_lru;
>  	unsigned char		c_state,	/* unused, inprog, done */
>  				c_type,		/* status, buffer */
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 230cc83921ad..e2fe0e9ce0df 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -30,6 +30,7 @@
>  #define TARGET_BUCKET_SIZE	64
>  
>  struct nfsd_drc_bucket {
> +	struct rb_root rb_head;
>  	struct list_head lru_head;
>  	spinlock_t cache_lock;
>  };
> @@ -129,6 +130,7 @@ nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum)
>  	if (rp) {
>  		rp->c_state = RC_UNUSED;
>  		rp->c_type = RC_NOCACHE;
> +		RB_CLEAR_NODE(&rp->c_node);
>  		INIT_LIST_HEAD(&rp->c_lru);
>  
>  		memset(&rp->c_key, 0, sizeof(rp->c_key));
> @@ -145,13 +147,14 @@ nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum)
>  }
>  
>  static void
> -nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
> +nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
>  {
>  	if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
>  		drc_mem_usage -= 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(&num_drc_entries);
>  		drc_mem_usage -= sizeof(*rp);
> @@ -163,7 +166,7 @@ static void
>  nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
>  {
>  	spin_lock(&b->cache_lock);
> -	nfsd_reply_cache_free_locked(rp);
> +	nfsd_reply_cache_free_locked(b, rp);
>  	spin_unlock(&b->cache_lock);
>  }
>  
> @@ -219,7 +222,7 @@ void nfsd_reply_cache_shutdown(void)
>  		struct list_head *head = &drc_hashtbl[i].lru_head;
>  		while (!list_empty(head)) {
>  			rp = list_first_entry(head, struct svc_cacherep, c_lru);
> -			nfsd_reply_cache_free_locked(rp);
> +			nfsd_reply_cache_free_locked(&drc_hashtbl[i], rp);
>  		}
>  	}
>  
> @@ -258,7 +261,7 @@ prune_bucket(struct nfsd_drc_bucket *b)
>  		if (atomic_read(&num_drc_entries) <= max_drc_entries &&
>  		    time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
>  			break;
> -		nfsd_reply_cache_free_locked(rp);
> +		nfsd_reply_cache_free_locked(b, rp);
>  		freed++;
>  	}
>  	return freed;
> @@ -349,17 +352,29 @@ static struct svc_cacherep *
>  nfsd_cache_insert(struct nfsd_drc_bucket *b, struct svc_cacherep *key)
>  {
>  	struct svc_cacherep	*rp, *ret = key;
> -	struct list_head 	*rh = &b->lru_head;
> +	struct rb_node		**p = &b->rb_head.rb_node,
> +				*parent = NULL;
>  	unsigned int		entries = 0;
> +	int cmp;
>  
> -	list_for_each_entry(rp, rh, c_lru) {
> +	while (*p != NULL) {
>  		++entries;
> -		if (nfsd_cache_key_cmp(key, rp) == 0) {
> +		parent = *p;
> +		rp = rb_entry(parent, struct svc_cacherep, c_node);
> +
> +		cmp = nfsd_cache_key_cmp(key, rp);
> +		if (cmp < 0)
> +			p = &parent->rb_left;
> +		else if (cmp > 0)
> +			p = &parent->rb_right;
> +		else {
>  			ret = rp;
> -			break;
> +			goto out;
>  		}
>  	}
> -
> +	rb_link_node(&key->c_node, parent, p);
> +	rb_insert_color(&key->c_node, &b->rb_head);
> +out:
>  	/* tally hash chain length stats */
>  	if (entries > longest_chain) {
>  		longest_chain = entries;
> @@ -414,7 +429,7 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
>  	spin_lock(&b->cache_lock);
>  	found = nfsd_cache_insert(b, rp);
>  	if (found != rp) {
> -		nfsd_reply_cache_free_locked(rp);
> +		nfsd_reply_cache_free_locked(NULL, rp);
>  		rp = found;
>  		goto found_entry;
>  	}
> @@ -462,7 +477,7 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
>  		break;
>  	default:
>  		printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
> -		nfsd_reply_cache_free_locked(rp);
> +		nfsd_reply_cache_free_locked(b, rp);
>  	}
>  
>  	goto out;
> -- 
> 2.17.1