Use the same API as the example code.

Allow the initial hash value to be passed in, as the examples do.
Incrementally hash in the dvp->v_id (using the official api) rather than
add it.  This seems to help power-of-two predictable filename trees
where the filenames repeat on a power-of-two cycle and the directory trees
have power-of-two components in it.  The simple add then mask was causing
things like 12000+ entry collision chains while most other entries have
between 0 and 3 entries each.  This way seems to improve things.

1 files changed, 8 insertions, 6 deletions

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 3f92c8f..3459917 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -86,8 +86,8 @@ struct	namecache {
 /*
  * Structures associated with name cacheing.
  */
-#define NCHHASH(dvp, hash) \
-	(&nchashtbl[((dvp)->v_id + (hash)) & nchash])
+#define NCHHASH(hash) \
+	(&nchashtbl[(hash) & nchash])
 static LIST_HEAD(nchashhead, namecache) *nchashtbl;	/* Hash Table */
 static TAILQ_HEAD(, namecache) ncneg;	/* Hash Table */
 static u_long	nchash;			/* size of hash table */
@@ -208,8 +208,9 @@ cache_lookup(dvp, vpp, cnp)
 		}
 	}
 
-	hash = fnv32_hashbuf(cnp->cn_nameptr, cnp->cn_namelen);
-	LIST_FOREACH(ncp, (NCHHASH(dvp, hash)), nc_hash) {
+	hash = fnv_32_buf(cnp->cn_nameptr, cnp->cn_namelen, FNV1_32_INIT);
+	hash = fnv_32_buf(&dvp->v_id, sizeof(dvp->v_id), hash);
+	LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
 		numchecks++;
 		if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
 		    !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen))
@@ -318,9 +319,10 @@ cache_enter(dvp, vp, cnp)
 	ncp->nc_vp = vp;
 	ncp->nc_dvp = dvp;
 	len = ncp->nc_nlen = cnp->cn_namelen;
-	hash = fnv32_hashbuf(cnp->cn_nameptr, len);
+	hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT);
 	bcopy(cnp->cn_nameptr, ncp->nc_name, len);
-	ncpp = NCHHASH(dvp, hash);
+	hash = fnv_32_buf(&dvp->v_id, sizeof(dvp->v_id), hash);
+	ncpp = NCHHASH(hash);
 	LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
 	if (LIST_EMPTY(&dvp->v_cache_src))
 		vhold(dvp);