---

yaml
---
r: 372163
b: refs/heads/master
c: 0733c7b
h: refs/heads/master
i:
  372161: 5cf953a
  372159: e2c2b44
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 98d821bda189ba2bfcb3877ea3064da3403698ae
+refs/heads/master: 0733c7ba1ef0d7e29a11c52f4d1356fc394de334

trunk/fs/nfsd/nfscache.c

@@ -11,14 +11,21 @@
 #include <linux/slab.h>
 #include <linux/sunrpc/addr.h>
 #include <linux/highmem.h>
+#include <linux/log2.h>
+#include <linux/hash.h>
 #include <net/checksum.h>
 
 #include "nfsd.h"
 #include "cache.h"
 
 #define NFSDDBG_FACILITY	NFSDDBG_REPCACHE
 
-#define HASHSIZE		64
+/*
+ * We use this value to determine the number of hash buckets from the max
+ * cache size, the idea being that when the cache is at its maximum number
+ * of entries, then this should be the average number of entries per bucket.
+ */
+#define TARGET_BUCKET_SIZE	64
 
 static struct hlist_head *	cache_hash;
 static struct list_head 	lru_head;
@@ -27,6 +34,9 @@ static struct kmem_cache	*drc_slab;
 /* max number of entries allowed in the cache */
 static unsigned int		max_drc_entries;
 
+/* number of significant bits in the hash value */
+static unsigned int		maskbits;
+
 /*
  * Stats and other tracking of on the duplicate reply cache. All of these and
  * the "rc" fields in nfsdstats are protected by the cache_lock
@@ -47,16 +57,6 @@ static unsigned int		longest_chain;
 /* size of cache when we saw the longest hash chain */
 static unsigned int		longest_chain_cachesize;
 
-/*
- * Calculate the hash index from an XID.
- */
-static inline u32 request_hash(u32 xid)
-{
-	u32 h = xid;
-	h ^= (xid >> 24);
-	return h & (HASHSIZE-1);
-}
-
 static int	nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
 static void	cache_cleaner_func(struct work_struct *unused);
 static int 	nfsd_reply_cache_shrink(struct shrinker *shrink,
@@ -103,6 +103,16 @@ nfsd_cache_size_limit(void)
 	return min_t(unsigned int, limit, 256*1024);
 }
 
+/*
+ * Compute the number of hash buckets we need. Divide the max cachesize by
+ * the "target" max bucket size, and round up to next power of two.
+ */
+static unsigned int
+nfsd_hashsize(unsigned int limit)
+{
+	return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE);
+}
+
 static struct svc_cacherep *
 nfsd_reply_cache_alloc(void)
 {
@@ -143,17 +153,21 @@ nfsd_reply_cache_free(struct svc_cacherep *rp)
 
 int nfsd_reply_cache_init(void)
 {
+	unsigned int hashsize;
+
 	INIT_LIST_HEAD(&lru_head);
 	max_drc_entries = nfsd_cache_size_limit();
 	num_drc_entries = 0;
+	hashsize = nfsd_hashsize(max_drc_entries);
+	maskbits = ilog2(hashsize);
 
 	register_shrinker(&nfsd_reply_cache_shrinker);
 	drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
 					0, 0, NULL);
 	if (!drc_slab)
 		goto out_nomem;
 
-	cache_hash = kcalloc(HASHSIZE, sizeof(struct hlist_head), GFP_KERNEL);
+	cache_hash = kcalloc(hashsize, sizeof(struct hlist_head), GFP_KERNEL);
 	if (!cache_hash)
 		goto out_nomem;
 
@@ -204,7 +218,7 @@ 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));
+	hlist_add_head(&rp->c_hash, cache_hash + hash_32(rp->c_xid, maskbits));
 }
 
 static inline bool
@@ -329,7 +343,7 @@ nfsd_cache_search(struct svc_rqst *rqstp, __wsum csum)
 	struct hlist_head 	*rh;
 	unsigned int		entries = 0;
 
-	rh = &cache_hash[request_hash(rqstp->rq_xid)];
+	rh = &cache_hash[hash_32(rqstp->rq_xid, maskbits)];
 	hlist_for_each_entry(rp, rh, c_hash) {
 		++entries;
 		if (nfsd_cache_match(rqstp, csum, rp)) {
@@ -588,7 +602,7 @@ static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
 	spin_lock(&cache_lock);
 	seq_printf(m, "max entries:           %u\n", max_drc_entries);
 	seq_printf(m, "num entries:           %u\n", num_drc_entries);
-	seq_printf(m, "hash buckets:          %u\n", HASHSIZE);
+	seq_printf(m, "hash buckets:          %u\n", 1 << maskbits);
 	seq_printf(m, "mem usage:             %u\n", drc_mem_usage);
 	seq_printf(m, "cache hits:            %u\n", nfsdstats.rchits);
 	seq_printf(m, "cache misses:          %u\n", nfsdstats.rcmisses);