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@xxxxxxx>
---
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
--
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