Clean up and improve the namecache.

1. We always keep one 16th of the vnodes on the freelist, so that the
namecache doesn't get trashed.  It used to be that it wasn't a problem, but
the only vnodes getting released these days are directories and things which
gets forced out of the VM/cache.  The latter is not numerous enough to keep
the pool of vnodes needed for the namecache sufficiently big.

2. Purge invalid entries in the namecache as soon as we notice them.  This
avoids a stale entry pushing out a valid entry on the LRU list.

3. Speed up the lookup in the namecache by avoid a special case branch.

4. Make the cache purge routines do the thing they're supposed to, and in
a decently efficient manner.

5. Make the size of the namecache follow the number of vnodes, so that we
can always point to all the vnodes we have in core.

6. Readability has gone way up.

7. Added a "options NCH_STATISTICS" feature that will gather more
detailed statistics on the performance of the namecache.

Reviewed by:	davidg

1 files changed, 130 insertions, 105 deletions

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 2faf829..e8ebe87 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -1,6 +1,8 @@
 /*
  * Copyright (c) 1989, 1993
  *	The Regents of the University of California.  All rights reserved.
+ * Copyright (c) 1995
+ *	Poul-Henning Kamp.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -31,7 +33,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)vfs_cache.c	8.3 (Berkeley) 8/22/94
- * $Id: vfs_cache.c,v 1.6 1995/03/08 01:08:03 phk Exp $
+ * $Id: vfs_cache.c,v 1.7 1995/03/08 01:40:44 phk Exp $
  */
 
 #include <sys/param.h>
@@ -52,6 +54,10 @@
  * obtained from (vp, name) where vp refers to the directory
  * containing name.
  *
+ * If it is a "negative" entry, (that we know a name to >not< exist)
+ * we point out entry at our own "nchENOENT", to avoid too much special
+ * casing in the inner loops of lookup.
+ *
  * For simplicity (and economy of storage), names longer than
  * a maximum length of NCHNAMLEN are not cached; they occur
  * infrequently in any case, and are almost never of interest.
@@ -65,27 +71,49 @@
  * Structures associated with name cacheing.
  */
 LIST_HEAD(nchashhead, namecache) *nchashtbl;	/* Hash Table */
+TAILQ_HEAD(, namecache) nclruhead;	/* LRU chain */
 u_long	nchash;				/* size of hash table - 1 */
-long	numcache;			/* number of cache entries allocated */
-TAILQ_HEAD(, namecache) nclruhead;		/* LRU chain */
 struct	nchstats nchstats;		/* cache effectiveness statistics */
-
+struct vnode nchENOENT;		/* our own "novnode" */
 int doingcache = 1;			/* 1 => enable the cache */
 
+#ifdef NCH_STATISTICS
+u_long	nchnbr;
+#define NCHNBR(ncp) (ncp)->nc_nbr = ++nchnbr;
+#define NCHHIT(ncp) (ncp)->nc_hits++
+#else
+#define NCHNBR(ncp)
+#define NCHHIT(ncp)
+#endif
+
+#define PURGE(ncp)  {						\
+	LIST_REMOVE(ncp, nc_hash);				\
+	ncp->nc_hash.le_prev = 0;				\
+	TAILQ_REMOVE(&nclruhead, ncp, nc_lru);			\
+	TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru); }
+
+#define TOUCH(ncp)  {						\
+	if (ncp->nc_lru.tqe_next == 0) { } else {		\
+		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);		\
+		TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);	\
+		NCHNBR(ncp); } }
+
 /*
- * Look for a the name in the cache. We don't do this
- * if the segment name is long, simply so the cache can avoid
- * holding long names (which would either waste space, or
+ * Lookup an entry in the cache 
+ *
+ * We don't do this if the segment name is long, simply so the cache 
+ * can avoid holding long names (which would either waste space, or
  * add greatly to the complexity).
  *
- * Lookup is called with ni_dvp pointing to the directory to search,
- * ni_ptr pointing to the name of the entry being sought, ni_namelen
- * tells the length of the name, and ni_hash contains a hash of
- * the name. If the lookup succeeds, the vnode is returned in ni_vp
- * and a status of -1 is returned. If the lookup determines that
- * the name does not exist (negative cacheing), a status of ENOENT
- * is returned. If the lookup fails, a status of zero is returned.
+ * Lookup is called with dvp pointing to the directory to search,
+ * cnp pointing to the name of the entry being sought.
+ * If the lookup succeeds, the vnode is returned in *vpp, and a status 
+ * of -1 is returned.
+ * If the lookup determines that the name does not exist (negative cacheing),
+ * a status of ENOENT is returned.
+ * If the lookup fails, a status of zero is returned.
  */
+
 int
 cache_lookup(dvp, vpp, cnp)
 	struct vnode *dvp;
@@ -99,77 +127,65 @@ cache_lookup(dvp, vpp, cnp)
 		cnp->cn_flags &= ~MAKEENTRY;
 		return (0);
 	}
+
 	if (cnp->cn_namelen > NCHNAMLEN) {
 		nchstats.ncs_long++;
 		cnp->cn_flags &= ~MAKEENTRY;
 		return (0);
 	}
+
 	ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) & nchash];
 	for (ncp = ncpp->lh_first; ncp != 0; ncp = nnp) {
-		if (ncp->nc_dvp == dvp &&
-		    ncp->nc_dvpid == dvp->v_id &&
-		    ncp->nc_nlen == cnp->cn_namelen &&
-		    !bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
-			break;
 		nnp = ncp->nc_hash.le_next;
 		/* If one of the vp's went stale, don't bother anymore. */
 		if ((ncp->nc_dvpid != ncp->nc_dvp->v_id) ||
-			(ncp->nc_vp && (ncp->nc_vpid != ncp->nc_vp->v_id))) {
-			LIST_REMOVE(ncp, nc_hash);
-			ncp->nc_hash.le_prev = 0;
-			TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
-			TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru);
+		    (ncp->nc_vpid  != ncp->nc_vp->v_id)) {
+			PURGE(ncp);
+			continue;
 		}
+		/* Now that we know the vp's to be valid, is it ours ? */
+		if (ncp->nc_dvp == dvp &&
+		    ncp->nc_nlen == cnp->cn_namelen &&
+		    !bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
+			goto found;	/* Fanatism considered bad. */
 	}
-	if (ncp == 0) {
-		nchstats.ncs_miss++;
-		return (0);
-	}
+	nchstats.ncs_miss++;
+	return (0);
+
+    found:
+	NCHHIT(ncp);
+
+	/* We don't want to have an entry, so dump it */
 	if ((cnp->cn_flags & MAKEENTRY) == 0) {
 		nchstats.ncs_badhits++;
-	} else if (ncp->nc_vp == NULL) {
-		if (cnp->cn_nameiop != CREATE) {
-			nchstats.ncs_neghits++;
-			/*
-			 * Move this slot to end of LRU chain,
-			 * if not already there.
-			 */
-			if (ncp->nc_lru.tqe_next != 0) {
-				TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
-				TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
-			}
-			return (ENOENT);
-		}
-	} else if (ncp->nc_vpid != ncp->nc_vp->v_id) {
-		nchstats.ncs_falsehits++;
-	} else {
+		PURGE(ncp);
+		return (0);
+	} 
+
+	/* We found a "positive" match, return the vnode */
+        if (ncp->nc_vp != &nchENOENT) {
 		nchstats.ncs_goodhits++;
-		/*
-		 * move this slot to end of LRU chain, if not already there
-		 */
-		if (ncp->nc_lru.tqe_next != 0) {
-			TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
-			TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
-		}
+		TOUCH(ncp);
 		*vpp = ncp->nc_vp;
 		return (-1);
 	}
 
-	/*
-	 * Last component and we are renaming or deleting,
-	 * the cache entry is invalid, or otherwise don't
-	 * want cache entry to exist.
-	 */
-	TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
-	LIST_REMOVE(ncp, nc_hash);
-	ncp->nc_hash.le_prev = 0;
-	TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru);
-	return (0);
+	/* We found a negative match, and want to create it, so purge */
+	if (cnp->cn_nameiop == CREATE) {
+		PURGE(ncp);
+		return (0);
+	}
+
+	/* The name does not exists */
+	nchstats.ncs_neghits++;
+	TOUCH(ncp);
+	return (ENOENT);
 }
 
 /*
- * Add an entry to the cache
+ * Add an entry to the cache.
  */
+
 void
 cache_enter(dvp, vp, cnp)
 	struct vnode *dvp;
@@ -179,35 +195,39 @@ cache_enter(dvp, vp, cnp)
 	register struct namecache *ncp;
 	register struct nchashhead *ncpp;
 
-#ifdef DIAGNOSTIC
-	if (cnp->cn_namelen > NCHNAMLEN)
-		panic("cache_enter: name too long");
-#endif
 	if (!doingcache)
 		return;
-	/*
-	 * Free the cache slot at head of lru chain.
-	 */
-	if (numcache < desiredvnodes) {
+
+	if (cnp->cn_namelen > NCHNAMLEN) {
+		printf("cache_enter: name too long");
+		return;
+	}
+
+	if (numcache < numvnodes) {
+		/* Add one more entry */
 		ncp = (struct namecache *)
 			malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
 		bzero((char *)ncp, sizeof *ncp);
 		numcache++;
 	} else if (ncp = nclruhead.tqh_first) {
+		/* reuse an old entry */
 		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
 		if (ncp->nc_hash.le_prev != 0) {
 			LIST_REMOVE(ncp, nc_hash);
 			ncp->nc_hash.le_prev = 0;
 		}
-	} else
+	} else {
+		/* give up */
 		return;
-	/* grab the vnode we just found */
-	ncp->nc_vp = vp;
-	if (vp)
-		ncp->nc_vpid = vp->v_id;
-	else
-		ncp->nc_vpid = 0;
+	}
+
+	/* If vp is NULL this is a "negative" cache entry */
+	if (!vp)
+		vp = &nchENOENT;
+
 	/* fill in cache info */
+	ncp->nc_vp = vp;
+	ncp->nc_vpid = vp->v_id;
 	ncp->nc_dvp = dvp;
 	ncp->nc_dvpid = dvp->v_id;
 	ncp->nc_nlen = cnp->cn_namelen;
@@ -220,66 +240,71 @@ cache_enter(dvp, vp, cnp)
 /*
  * Name cache initialization, from vfs_init() when we are booting
  */
+
 void
 nchinit()
 {
 
 	TAILQ_INIT(&nclruhead);
 	nchashtbl = hashinit(desiredvnodes, M_CACHE, &nchash);
+	nchENOENT.v_id = 1;
 }
 
 /*
- * Cache flush, a particular vnode; called when a vnode is renamed to
- * hide entries that would now be invalid
+ * Invalidate a all entries to particular vnode.
+ * 
+ * We actually just increment the v_id, that will do it.  The entries will
+ * be purged by lookup as they get found.
+ * If the v_id wraps around, we need to ditch the entire cache, to avoid
+ * confusion.
+ * No valid vnode will ever have (v_id == 0).
  */
+
 void
 cache_purge(vp)
 	struct vnode *vp;
 {
-	struct namecache *ncp;
 	struct nchashhead *ncpp;
 
 	vp->v_id = ++nextvnodeid;
 	if (nextvnodeid != 0)
 		return;
 	for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
-		for (ncp = ncpp->lh_first; ncp != 0; ncp = ncp->nc_hash.le_next) {
-			ncp->nc_vpid = 0;
-			ncp->nc_dvpid = 0;
-		}
+		while(ncpp->lh_first)
+			PURGE(ncpp->lh_first);
 	}
 	vp->v_id = ++nextvnodeid;
 }
 
 /*
- * Cache flush, a whole filesystem; called when filesys is umounted to
- * remove entries that would now be invalid
+ * Flush all entries referencing a particular filesystem.
  *
- * The line "nxtcp = nchhead" near the end is to avoid potential problems
- * if the cache lru chain is modified while we are dumping the
- * inode.  This makes the algorithm O(n^2), but do you think I care?
+ * Since we need to check it anyway, we will flush all the invalid
+ * entriess at the same time.
+ *
+ * If we purge anything, we scan the hash-bucket again.  There is only
+ * a handful of entries, so it cheap and simple.
  */
+
 void
 cache_purgevfs(mp)
 	struct mount *mp;
 {
-	register struct namecache *ncp, *nxtcp;
+	struct nchashhead *ncpp;
+	struct namecache *ncp, *nxtcp;
 
-	for (ncp = nclruhead.tqh_first; ncp != 0; ncp = nxtcp) {
-		if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp) {
-			nxtcp = ncp->nc_lru.tqe_next;
-			continue;
-		}
-		/* free the resources we had */
-		ncp->nc_vp = NULL;
-		ncp->nc_dvp = NULL;
-		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
-		if (ncp->nc_hash.le_prev != 0) {
-			LIST_REMOVE(ncp, nc_hash);
-			ncp->nc_hash.le_prev = 0;
+	/* Scan hash tables for applicable entries */
+	for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
+		ncp = ncpp->lh_first;
+		while(ncp) {
+			if (ncp->nc_dvpid != ncp->nc_dvp->v_id ||
+			    ncp->nc_vpid != ncp->nc_vp->v_id ||
+			    ncp->nc_dvp->v_mount == mp) {
+				PURGE(ncp);
+				ncp = ncpp->lh_first;
+			} else {
+				ncp = ncp->nc_lru.tqe_next;
+			}
 		}
-		/* cause rescan of list, it may have altered */
-		nxtcp = nclruhead.tqh_first;
-		TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru);
 	}
 }