[patch 16/29] knfsd: use client IPv4 address in reply cache hash

[Greg Banks <gnb@sgi.com>]

Use the IPv4 address of the client in the reply cache hash function.
This can help improve the distribution of the hash function when the
workload includes a large number of clients which mounted their NFS
filesystems at nearly the same time and are doing similar sequences
of NFS calls, a pattern seen with large compute clusters.

This code predates the IPv6 support in the current NFS server but
should be harmless with IPv6 clients.

Signed-off-by: Greg Banks <gnb@sgi.com>
---

 fs/nfsd/nfscache.c |   27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

Index: bfields/fs/nfsd/nfscache.c
===================================================================
--- bfields.orig/fs/nfsd/nfscache.c
+++ bfields/fs/nfsd/nfscache.c
@@ -38,12 +38,17 @@ static int			cache_disabled = 1;
  * Calculate the hash index from an XID.  Note, some clients increment
  * their XIDs in host order, which can result in all the variation being
  * in the top bits we see here.  So we fold those bits down.
+ *
+ * Experiment shows that using the Jenkins hash improves the spectral
+ * properties of this hash, but the CPU cost of calculating it outweighs
+ * the advantages.
  */
-static inline u32 request_hash(u32 xid)
+static inline u32 request_hash(u32 xid, const struct sockaddr_in *sin)
 {
 	u32 h = xid;
 	h ^= (xid >> 24);
 	h ^= ((xid & 0xff0000) >> 8);
+	h ^= sin->sin_addr.s_addr;
 	return h & (HASHSIZE-1);
 }
 
@@ -114,16 +119,6 @@ lru_put_end(struct svc_cacherep *rp)
 }
 
 /*
- * Move a cache entry from one hash list to another
- */
-static void
-hash_refile(struct svc_cacherep *rp)
-{
-	hlist_del_init(&rp->c_hash);
-	hlist_add_head(&rp->c_hash, cache_hash + request_hash(rp->c_xid));
-}
-
-/*
  * Try to find an entry matching the current call in the cache. When none
  * is found, we grab the oldest unlocked entry off the LRU list.
  * Note that no operation within the loop may sleep.
@@ -137,7 +132,8 @@ nfsd_cache_lookup(struct svc_rqst *rqstp
 	__be32			xid = rqstp->rq_xid;
 	u32			proto =  rqstp->rq_prot,
 				vers = rqstp->rq_vers,
-				proc = rqstp->rq_proc;
+				proc = rqstp->rq_proc,
+				h;
 	unsigned long		age;
 	int rtn;
 
@@ -146,11 +142,12 @@ nfsd_cache_lookup(struct svc_rqst *rqstp
 		nfsdstats.rcnocache++;
 		return RC_DOIT;
 	}
+	h = request_hash(xid, svc_addr_in(rqstp));
 
 	spin_lock(&cache_lock);
 	rtn = RC_DOIT;
 
-	rh = &cache_hash[request_hash(xid)];
+	rh = &cache_hash[h];
 	hlist_for_each_entry(rp, hn, rh, c_hash) {
 		if (rp->c_state != RC_UNUSED &&
 		    xid == rp->c_xid && proc == rp->c_proc &&
@@ -198,7 +195,9 @@ nfsd_cache_lookup(struct svc_rqst *rqstp
 	rp->c_vers = vers;
 	rp->c_timestamp = jiffies;
 
-	hash_refile(rp);
+	/* Move the cache entry from one hash list to another */
+	hlist_del_init(&rp->c_hash);
+	hlist_add_head(&rp->c_hash, cache_hash + h);
 
 	/* release any buffer */
 	if (rp->c_type == RC_REPLBUFF) {

--
Greg