Make the VFS cache use zones instead of malloc(9). This results in a

small but noticeable increase in performance for name lookup operations.

The code uses two zones, one for short names (less than 32 characters)
and one for long names (up to NAME_MAX).  Since most file names are
fairly short, this saves a considerable amount of space that would
otherwise be wasted if we always allocated NAME_MAX bytes.  The cutoff
value of 32 characters was picked arbitrarily and may benefit from some
tweaking; it could also be made into a tunable.

Submitted by:	hmp

1 files changed, 33 insertions, 4 deletions

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 0c66a1c..fff5024 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -55,6 +55,8 @@ __FBSDID("$FreeBSD$");
 #include <sys/filedesc.h>
 #include <sys/fnv_hash.h>
 
+#include <vm/uma.h>
+
 /*
  * This structure describes the elements in the cache of recent
  * names looked up by namei.
@@ -111,6 +113,28 @@ SYSCTL_ULONG(_debug, OID_AUTO, numcachepl, CTLFLAG_RD, &numcachepl, 0, "");
 #endif
 struct	nchstats nchstats;		/* cache effectiveness statistics */
 
+/*
+ * UMA zones for the VFS cache.
+ *
+ * The small cache is used for entries with short names, which are the
+ * most common.  The large cache is used for entries which are too big to
+ * fit in the small cache.
+ */
+static uma_zone_t cache_zone_small;
+static uma_zone_t cache_zone_large;
+
+#define	CACHE_PATH_CUTOFF	32
+#define	CACHE_ZONE_SMALL	(sizeof(struct namecache) + CACHE_PATH_CUTOFF)
+#define	CACHE_ZONE_LARGE	(sizeof(struct namecache) + NAME_MAX)
+
+#define cache_alloc(len)	uma_zalloc(((len) <= CACHE_PATH_CUTOFF) ? \
+	cache_zone_small : cache_zone_large, M_WAITOK)
+#define cache_free(ncp)		do { \
+	if (ncp != NULL) \
+		uma_zfree(((ncp)->nc_nlen <= CACHE_PATH_CUTOFF) ? \
+		    cache_zone_small : cache_zone_large, (ncp)); \
+} while (0)
+
 static int	doingcache = 1;		/* 1 => enable the cache */
 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, "");
 
@@ -253,7 +277,7 @@ cache_zap(ncp)
 		numneg--;
 	}
 	numcache--;
-	free(ncp, M_VFSCACHE);
+	cache_free(ncp);
 }
 
 /*
@@ -418,9 +442,8 @@ cache_enter(dvp, vp, cnp)
 		}
 	}
 
-	ncp = (struct namecache *)
-		malloc(sizeof *ncp + cnp->cn_namelen, M_VFSCACHE, M_WAITOK);
-	bzero((char *)ncp, sizeof *ncp);
+	ncp = cache_alloc(cnp->cn_namelen);
+	/* XXX can uma_zalloc(..., M_WAITOK) fail? */
 	numcache++;
 	if (!vp) {
 		numneg++;
@@ -472,6 +495,12 @@ nchinit(void *dummy __unused)
 {
 
 	TAILQ_INIT(&ncneg);
+
+	cache_zone_small = uma_zcreate("S VFS Cache", CACHE_ZONE_SMALL, NULL,
+	    NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
+	cache_zone_large = uma_zcreate("L VFS Cache", CACHE_ZONE_LARGE, NULL,
+	    NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
+
 	nchashtbl = hashinit(desiredvnodes * 2, M_VFSCACHE, &nchash);
 }
 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL)