knfsd: Improve lookup performance in the duplicate reply cache using an rbtree

Use an rbtree to ensure the lookup/insert of an entry in a DRC bucket is
O(log(N)).
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/cache.h

@@ -30,6 +30,7 @@ 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 */

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;