xref: /src/sys/kern/vfs_cache.c

/*	$NetBSD: vfs_cache.c,v 1.76 2008/05/05 17:11:17 ad Exp $	*/

/*-
 * Copyright (c) 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)vfs_cache.c	8.3 (Berkeley) 8/22/94
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.76 2008/05/05 17:11:17 ad Exp $");

#include "opt_ddb.h"
#include "opt_revcache.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/mount.h>
#include <sys/vnode.h>
#include <sys/namei.h>
#include <sys/errno.h>
#include <sys/pool.h>
#include <sys/mutex.h>
#include <sys/atomic.h>
#include <sys/kthread.h>
#include <sys/kernel.h>
#include <sys/cpu.h>
#include <sys/evcnt.h>

#define NAMECACHE_ENTER_REVERSE
/*
 * Name caching works as follows:
 *
 * Names found by directory scans are retained in a cache
 * for future reference.  It is managed LRU, so frequently
 * used names will hang around.  Cache is indexed by hash value
 * obtained from (dvp, name) where dvp refers to the directory
 * containing name.
 *
 * 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.
 *
 * Upon reaching the last segment of a path, if the reference
 * is for DELETE, or NOCACHE is set (rewrite), and the
 * name is located in the cache, it will be dropped.
 * The entry is dropped also when it was not possible to lock
 * the cached vnode, either because vget() failed or the generation
 * number has changed while waiting for the lock.
 */

/*
 * Structures associated with name cacheing.
 */
LIST_HEAD(nchashhead, namecache) *nchashtbl;
u_long	nchash;				/* size of hash table - 1 */
#define	NCHASH(cnp, dvp)	\
	(((cnp)->cn_hash ^ ((uintptr_t)(dvp) >> 3)) & nchash)

LIST_HEAD(ncvhashhead, namecache) *ncvhashtbl;
u_long	ncvhash;			/* size of hash table - 1 */
#define	NCVHASH(vp)		(((uintptr_t)(vp) >> 3) & ncvhash)

long	numcache;			/* number of cache entries allocated */
static u_int	cache_gcpend;		/* number of entries pending GC */
static void	*cache_gcqueue;		/* garbage collection queue */

TAILQ_HEAD(, namecache) nclruhead =		/* LRU chain */
	TAILQ_HEAD_INITIALIZER(nclruhead);
#define	COUNT(x)	nchstats.x++
struct	nchstats nchstats;		/* cache effectiveness statistics */

static pool_cache_t namecache_cache;

MALLOC_DEFINE(M_CACHE, "namecache", "Dynamically allocated cache entries");

int cache_lowat = 95;
int cache_hiwat = 98;
int cache_hottime = 5;			/* number of seconds */
int doingcache = 1;			/* 1 => enable the cache */

static struct evcnt cache_ev_scan;
static struct evcnt cache_ev_gc;
static struct evcnt cache_ev_over;
static struct evcnt cache_ev_under;
static struct evcnt cache_ev_forced;

/* A single lock to serialize modifications. */
static kmutex_t *namecache_lock;

static void cache_invalidate(struct namecache *);
static inline struct namecache *cache_lookup_entry(
    const struct vnode *, const struct componentname *);
static void cache_thread(void *);
static void cache_invalidate(struct namecache *);
static void cache_disassociate(struct namecache *);
static void cache_reclaim(void);
static int cache_ctor(void *, void *, int);
static void cache_dtor(void *, void *);

/*
 * Invalidate a cache entry and enqueue it for garbage collection.
 */
static void
cache_invalidate(struct namecache *ncp)
{
	void *head;

	KASSERT(mutex_owned(&ncp->nc_lock));

	if (ncp->nc_dvp != NULL) {
		ncp->nc_vp = NULL;
		ncp->nc_dvp = NULL;
		do {
			head = cache_gcqueue;
			ncp->nc_gcqueue = head;
		} while (atomic_cas_ptr(&cache_gcqueue, head, ncp) != head);
		atomic_inc_uint(&cache_gcpend);
	}
}

/*
 * Disassociate a namecache entry from any vnodes it is attached to,
 * and remove from the global LRU list.
 */
static void
cache_disassociate(struct namecache *ncp)
{

	KASSERT(mutex_owned(namecache_lock));
	KASSERT(ncp->nc_dvp == NULL);

	if (ncp->nc_lru.tqe_prev != NULL) {
		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
		ncp->nc_lru.tqe_prev = NULL;
	}
	if (ncp->nc_vhash.le_prev != NULL) {
		LIST_REMOVE(ncp, nc_vhash);
		ncp->nc_vhash.le_prev = NULL;
	}
	if (ncp->nc_vlist.le_prev != NULL) {
		LIST_REMOVE(ncp, nc_vlist);
		ncp->nc_vlist.le_prev = NULL;
	}
	if (ncp->nc_dvlist.le_prev != NULL) {
		LIST_REMOVE(ncp, nc_dvlist);
		ncp->nc_dvlist.le_prev = NULL;
	}
}

/*
 * Lock all CPUs to prevent any cache lookup activity.  Conceptually,
 * this locks out all "readers".
 */
static void
cache_lock_cpus(void)
{
	CPU_INFO_ITERATOR cii;
	struct cpu_info *ci;

	for (CPU_INFO_FOREACH(cii, ci)) {
		mutex_enter(ci->ci_data.cpu_cachelock);
	}
}

/*
 * Release all CPU locks.
 */
static void
cache_unlock_cpus(void)
{
	CPU_INFO_ITERATOR cii;
	struct cpu_info *ci;

	for (CPU_INFO_FOREACH(cii, ci)) {
		mutex_exit(ci->ci_data.cpu_cachelock);
	}
}

/*
 * Find a single cache entry and return it locked.  'namecache_lock' or
 * at least one of the per-CPU locks must be held.
 */
static struct namecache *
cache_lookup_entry(const struct vnode *dvp, const struct componentname *cnp)
{
	struct nchashhead *ncpp;
	struct namecache *ncp;

	ncpp = &nchashtbl[NCHASH(cnp, dvp)];

	LIST_FOREACH(ncp, ncpp, nc_hash) {
		if (ncp->nc_dvp != dvp ||
		    ncp->nc_nlen != cnp->cn_namelen ||
		    memcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
		    	continue;
	    	mutex_enter(&ncp->nc_lock);
		if (ncp->nc_dvp == dvp) {
			ncp->nc_hittime = hardclock_ticks;
			return ncp;
		}
		/* Raced: entry has been nullified. */
		mutex_exit(&ncp->nc_lock);
	}

	return NULL;
}

/*
 * 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
 * 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 locked, stored in ni_vp
 * and a status of zero is returned. If the locking fails for whatever
 * reason, the vnode is unlocked and the error is returned to caller.
 * 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 -1
 * is returned.
 */
int
cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
{
	struct namecache *ncp;
	struct vnode *vp;
	kmutex_t *cpulock;
	int error;

	if (!doingcache) {
		cnp->cn_flags &= ~MAKEENTRY;
		*vpp = NULL;
		return (-1);
	}

	if (cnp->cn_namelen > NCHNAMLEN) {
		/* Unlocked, but only for stats. */
		COUNT(ncs_long);
		cnp->cn_flags &= ~MAKEENTRY;
		goto fail;
	}
	cpulock = curcpu()->ci_data.cpu_cachelock;
	mutex_enter(cpulock);
	ncp = cache_lookup_entry(dvp, cnp);
	if (ncp == NULL) {
		COUNT(ncs_miss);
		goto fail_wlock;
	}
	if ((cnp->cn_flags & MAKEENTRY) == 0) {
		COUNT(ncs_badhits);
		goto remove;
	} else if (ncp->nc_vp == NULL) {
		/*
		 * Restore the ISWHITEOUT flag saved earlier.
		 */
		cnp->cn_flags |= ncp->nc_flags;
		if (cnp->cn_nameiop != CREATE ||
		    (cnp->cn_flags & ISLASTCN) == 0) {
			COUNT(ncs_neghits);
			mutex_exit(&ncp->nc_lock);
			mutex_exit(cpulock);
			return (ENOENT);
		} else {
			COUNT(ncs_badhits);
			goto remove;
		}
	}

	vp = ncp->nc_vp;
	mutex_enter(&vp->v_interlock);
	mutex_exit(&ncp->nc_lock);
	mutex_exit(cpulock);
	error = vget(vp, LK_NOWAIT | LK_INTERLOCK);

#ifdef DEBUG
	/*
	 * since we released nb->nb_lock,
	 * we can't use this pointer any more.
	 */
	ncp = NULL;
#endif /* DEBUG */

	if (error) {
		KASSERT(error == EBUSY);
		/*
		 * this vnode is being cleaned out.
		 */
		COUNT(ncs_falsehits); /* XXX badhits? */
		goto fail;
	}

	if (vp == dvp) {	/* lookup on "." */
		error = 0;
	} else if (cnp->cn_flags & ISDOTDOT) {
		VOP_UNLOCK(dvp, 0);
		error = vn_lock(vp, LK_EXCLUSIVE);
		vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
	} else {
		error = vn_lock(vp, LK_EXCLUSIVE);
	}

	/*
	 * Check that the lock succeeded.
	 */
	if (error) {
		/* Unlocked, but only for stats. */
		COUNT(ncs_badhits);
		*vpp = NULL;
		return (-1);
	}

	/* Unlocked, but only for stats. */
	COUNT(ncs_goodhits);
	*vpp = vp;
	return (0);

remove:
	/*
	 * Last component and we are renaming or deleting,
	 * the cache entry is invalid, or otherwise don't
	 * want cache entry to exist.
	 */
	cache_invalidate(ncp);
	mutex_exit(&ncp->nc_lock);
fail_wlock:
	mutex_exit(cpulock);
fail:
	*vpp = NULL;
	return (-1);
}

int
cache_lookup_raw(struct vnode *dvp, struct vnode **vpp,
    struct componentname *cnp)
{
	struct namecache *ncp;
	struct vnode *vp;
	kmutex_t *cpulock;
	int error;

	if (!doingcache) {
		cnp->cn_flags &= ~MAKEENTRY;
		*vpp = NULL;
		return (-1);
	}

	if (cnp->cn_namelen > NCHNAMLEN) {
		/* Unlocked, but only for stats. */
		COUNT(ncs_long);
		cnp->cn_flags &= ~MAKEENTRY;
		goto fail;
	}
	cpulock = curcpu()->ci_data.cpu_cachelock;
	mutex_enter(cpulock);
	ncp = cache_lookup_entry(dvp, cnp);
	if (ncp == NULL) {
		COUNT(ncs_miss);
		goto fail_wlock;
	}
	vp = ncp->nc_vp;
	if (vp == NULL) {
		/*
		 * Restore the ISWHITEOUT flag saved earlier.
		 */
		cnp->cn_flags |= ncp->nc_flags;
		COUNT(ncs_neghits);
		mutex_exit(&ncp->nc_lock);
		mutex_exit(cpulock);
		return (ENOENT);
	}
	mutex_enter(&vp->v_interlock);
	mutex_exit(&ncp->nc_lock);
	mutex_exit(cpulock);
	error = vget(vp, LK_NOWAIT | LK_INTERLOCK);

	if (error) {
		KASSERT(error == EBUSY);
		/*
		 * this vnode is being cleaned out.
		 */
		COUNT(ncs_falsehits); /* XXX badhits? */
		goto fail;
	}

	*vpp = vp;

	return 0;

fail_wlock:
	mutex_exit(cpulock);
fail:
	*vpp = NULL;
	return -1;
}

/*
 * Scan cache looking for name of directory entry pointing at vp.
 *
 * Fill in dvpp.
 *
 * If bufp is non-NULL, also place the name in the buffer which starts
 * at bufp, immediately before *bpp, and move bpp backwards to point
 * at the start of it.  (Yes, this is a little baroque, but it's done
 * this way to cater to the whims of getcwd).
 *
 * Returns 0 on success, -1 on cache miss, positive errno on failure.
 */
int
cache_revlookup(struct vnode *vp, struct vnode **dvpp, char **bpp, char *bufp)
{
	struct namecache *ncp;
	struct vnode *dvp;
	struct ncvhashhead *nvcpp;
	char *bp;

	if (!doingcache)
		goto out;

	nvcpp = &ncvhashtbl[NCVHASH(vp)];

	mutex_enter(namecache_lock);
	LIST_FOREACH(ncp, nvcpp, nc_vhash) {
		mutex_enter(&ncp->nc_lock);
		if (ncp->nc_vp == vp &&
		    (dvp = ncp->nc_dvp) != NULL &&
		    dvp != vp) { 		/* avoid pesky . entries.. */

#ifdef DIAGNOSTIC
			if (ncp->nc_nlen == 1 &&
			    ncp->nc_name[0] == '.')
				panic("cache_revlookup: found entry for .");

			if (ncp->nc_nlen == 2 &&
			    ncp->nc_name[0] == '.' &&
			    ncp->nc_name[1] == '.')
				panic("cache_revlookup: found entry for ..");
#endif
			COUNT(ncs_revhits);

			if (bufp) {
				bp = *bpp;
				bp -= ncp->nc_nlen;
				if (bp <= bufp) {
					*dvpp = NULL;
					mutex_exit(&ncp->nc_lock);
					mutex_exit(namecache_lock);
					return (ERANGE);
				}
				memcpy(bp, ncp->nc_name, ncp->nc_nlen);
				*bpp = bp;
			}

			/* XXX MP: how do we know dvp won't evaporate? */
			*dvpp = dvp;
			mutex_exit(&ncp->nc_lock);
			mutex_exit(namecache_lock);
			return (0);
		}
		mutex_exit(&ncp->nc_lock);
	}
	COUNT(ncs_revmiss);
	mutex_exit(namecache_lock);
 out:
	*dvpp = NULL;
	return (-1);
}

/*
 * Add an entry to the cache
 */
void
cache_enter(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
{
	struct namecache *ncp;
	struct namecache *oncp;
	struct nchashhead *ncpp;
	struct ncvhashhead *nvcpp;

#ifdef DIAGNOSTIC
	if (cnp->cn_namelen > NCHNAMLEN)
		panic("cache_enter: name too long");
#endif
	if (!doingcache)
		return;

	if (numcache > desiredvnodes) {
		mutex_enter(namecache_lock);
		cache_ev_forced.ev_count++;
		cache_reclaim();
		mutex_exit(namecache_lock);
	}

	ncp = pool_cache_get(namecache_cache, PR_WAITOK);
	mutex_enter(namecache_lock);
	numcache++;

	/*
	 * Concurrent lookups in the same directory may race for a
	 * cache entry.  if there's a duplicated entry, free it.
	 */
	oncp = cache_lookup_entry(dvp, cnp);
	if (oncp) {
		cache_invalidate(oncp);
		mutex_exit(&oncp->nc_lock);
	}

	/* Grab the vnode we just found. */
	mutex_enter(&ncp->nc_lock);
	ncp->nc_vp = vp;
	ncp->nc_flags = 0;
	ncp->nc_hittime = 0;
	ncp->nc_gcqueue = NULL;
	if (vp == NULL) {
		/*
		 * For negative hits, save the ISWHITEOUT flag so we can
		 * restore it later when the cache entry is used again.
		 */
		ncp->nc_flags = cnp->cn_flags & ISWHITEOUT;
	}
	/* Fill in cache info. */
	ncp->nc_dvp = dvp;
	LIST_INSERT_HEAD(&dvp->v_dnclist, ncp, nc_dvlist);
	if (vp)
		LIST_INSERT_HEAD(&vp->v_nclist, ncp, nc_vlist);
	else {
		ncp->nc_vlist.le_prev = NULL;
		ncp->nc_vlist.le_next = NULL;
	}
	ncp->nc_nlen = cnp->cn_namelen;
	TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
	memcpy(ncp->nc_name, cnp->cn_nameptr, (unsigned)ncp->nc_nlen);
	ncpp = &nchashtbl[NCHASH(cnp, dvp)];

	/*
	 * Flush updates before making visible in table.  No need for a
	 * memory barrier on the other side: to see modifications the
	 * list must be followed, meaning a dependent pointer load.
	 * The below is LIST_INSERT_HEAD() inlined, with the memory
	 * barrier included in the correct place.
	 */
	if ((ncp->nc_hash.le_next = ncpp->lh_first) != NULL)
		ncpp->lh_first->nc_hash.le_prev = &ncp->nc_hash.le_next;
	ncp->nc_hash.le_prev = &ncpp->lh_first;
	membar_producer();
	ncpp->lh_first = ncp;

	ncp->nc_vhash.le_prev = NULL;
	ncp->nc_vhash.le_next = NULL;

	/*
	 * Create reverse-cache entries (used in getcwd) for directories.
	 * (and in linux procfs exe node)
	 */
	if (vp != NULL &&
	    vp != dvp &&
#ifndef NAMECACHE_ENTER_REVERSE
	    vp->v_type == VDIR &&
#endif
	    (ncp->nc_nlen > 2 ||
	    (ncp->nc_nlen > 1 && ncp->nc_name[1] != '.') ||
	    (/* ncp->nc_nlen > 0 && */ ncp->nc_name[0] != '.'))) {
		nvcpp = &ncvhashtbl[NCVHASH(vp)];
		LIST_INSERT_HEAD(nvcpp, ncp, nc_vhash);
	}
	mutex_exit(&ncp->nc_lock);
	mutex_exit(namecache_lock);
}

/*
 * Name cache initialization, from vfs_init() when we are booting
 */
void
nchinit(void)
{
	int error;

	namecache_cache = pool_cache_init(sizeof(struct namecache),
	    coherency_unit, 0, 0, "ncache", NULL, IPL_NONE, cache_ctor,
	    cache_dtor, NULL);
	KASSERT(namecache_cache != NULL);

	namecache_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);

	nchashtbl = hashinit(desiredvnodes, HASH_LIST, true, &nchash);
	ncvhashtbl =
#ifdef NAMECACHE_ENTER_REVERSE
	    hashinit(desiredvnodes, HASH_LIST, true, &ncvhash);
#else
	    hashinit(desiredvnodes/8, HASH_LIST, true, &ncvhash);
#endif

	error = kthread_create(PRI_VM, KTHREAD_MPSAFE, NULL, cache_thread,
	    NULL, NULL, "cachegc");
	if (error != 0)
		panic("nchinit %d", error);

	evcnt_attach_dynamic(&cache_ev_scan, EVCNT_TYPE_MISC, NULL,
	   "namecache", "entries scanned");
	evcnt_attach_dynamic(&cache_ev_gc, EVCNT_TYPE_MISC, NULL,
	   "namecache", "entries collected");
	evcnt_attach_dynamic(&cache_ev_over, EVCNT_TYPE_MISC, NULL,
	   "namecache", "over scan target");
	evcnt_attach_dynamic(&cache_ev_under, EVCNT_TYPE_MISC, NULL,
	   "namecache", "under scan target");
	evcnt_attach_dynamic(&cache_ev_forced, EVCNT_TYPE_MISC, NULL,
	   "namecache", "forced reclaims");
}

static int
cache_ctor(void *arg, void *obj, int flag)
{
	struct namecache *ncp;

	ncp = obj;
	mutex_init(&ncp->nc_lock, MUTEX_DEFAULT, IPL_NONE);

	return 0;
}

static void
cache_dtor(void *arg, void *obj)
{
	struct namecache *ncp;

	ncp = obj;
	mutex_destroy(&ncp->nc_lock);
}

/*
 * Called once for each CPU in the system as attached.
 */
void
cache_cpu_init(struct cpu_info *ci)
{

	ci->ci_data.cpu_cachelock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);
}

/*
 * Name cache reinitialization, for when the maximum number of vnodes increases.
 */
void
nchreinit(void)
{
	struct namecache *ncp;
	struct nchashhead *oldhash1, *hash1;
	struct ncvhashhead *oldhash2, *hash2;
	u_long i, oldmask1, oldmask2, mask1, mask2;

	hash1 = hashinit(desiredvnodes, HASH_LIST, true, &mask1);
	hash2 =
#ifdef NAMECACHE_ENTER_REVERSE
	    hashinit(desiredvnodes, HASH_LIST, true, &mask2);
#else
	    hashinit(desiredvnodes/8, HASH_LIST, true, &mask2);
#endif
	mutex_enter(namecache_lock);
	cache_lock_cpus();
	oldhash1 = nchashtbl;
	oldmask1 = nchash;
	nchashtbl = hash1;
	nchash = mask1;
	oldhash2 = ncvhashtbl;
	oldmask2 = ncvhash;
	ncvhashtbl = hash2;
	ncvhash = mask2;
	for (i = 0; i <= oldmask1; i++) {
		while ((ncp = LIST_FIRST(&oldhash1[i])) != NULL) {
			LIST_REMOVE(ncp, nc_hash);
			ncp->nc_hash.le_prev = NULL;
		}
	}
	for (i = 0; i <= oldmask2; i++) {
		while ((ncp = LIST_FIRST(&oldhash2[i])) != NULL) {
			LIST_REMOVE(ncp, nc_vhash);
			ncp->nc_vhash.le_prev = NULL;
		}
	}
	cache_unlock_cpus();
	mutex_exit(namecache_lock);
	hashdone(oldhash1, HASH_LIST, oldmask1);
	hashdone(oldhash2, HASH_LIST, oldmask2);
}

/*
 * Cache flush, a particular vnode; called when a vnode is renamed to
 * hide entries that would now be invalid
 */
void
cache_purge1(struct vnode *vp, const struct componentname *cnp, int flags)
{
	struct namecache *ncp, *ncnext;

	mutex_enter(namecache_lock);
	if (flags & PURGE_PARENTS) {
		for (ncp = LIST_FIRST(&vp->v_nclist); ncp != NULL;
		    ncp = ncnext) {
			ncnext = LIST_NEXT(ncp, nc_vlist);
			mutex_enter(&ncp->nc_lock);
			cache_invalidate(ncp);
			mutex_exit(&ncp->nc_lock);
			cache_disassociate(ncp);
		}
	}
	if (flags & PURGE_CHILDREN) {
		for (ncp = LIST_FIRST(&vp->v_dnclist); ncp != NULL;
		    ncp = ncnext) {
			ncnext = LIST_NEXT(ncp, nc_dvlist);
			mutex_enter(&ncp->nc_lock);
			cache_invalidate(ncp);
			mutex_exit(&ncp->nc_lock);
			cache_disassociate(ncp);
		}
	}
	if (cnp != NULL) {
		ncp = cache_lookup_entry(vp, cnp);
		if (ncp) {
			cache_invalidate(ncp);
			cache_disassociate(ncp);
			mutex_exit(&ncp->nc_lock);
		}
	}
	mutex_exit(namecache_lock);
}

/*
 * Cache flush, a whole filesystem; called when filesys is umounted to
 * remove entries that would now be invalid.
 */
void
cache_purgevfs(struct mount *mp)
{
	struct namecache *ncp, *nxtcp;

	mutex_enter(namecache_lock);
	for (ncp = TAILQ_FIRST(&nclruhead); ncp != NULL; ncp = nxtcp) {
		nxtcp = TAILQ_NEXT(ncp, nc_lru);
		mutex_enter(&ncp->nc_lock);
		if (ncp->nc_dvp != NULL && ncp->nc_dvp->v_mount == mp) {
			/* Free the resources we had. */
			cache_invalidate(ncp);
			cache_disassociate(ncp);
		}
		mutex_exit(&ncp->nc_lock);
	}
	cache_reclaim();
	mutex_exit(namecache_lock);
}

/*
 * Scan global list invalidating entries until we meet a preset target.
 * Prefer to invalidate entries that have not scored a hit within
 * cache_hottime seconds.  We sort the LRU list only for this routine's
 * benefit.
 */
static void
cache_prune(int incache, int target)
{
	struct namecache *ncp, *nxtcp, *sentinel;
	int items, recent, tryharder;

	KASSERT(mutex_owned(namecache_lock));

	items = 0;
	tryharder = 0;
	recent = hardclock_ticks - hz * cache_hottime;
	sentinel = NULL;
	for (ncp = TAILQ_FIRST(&nclruhead); ncp != NULL; ncp = nxtcp) {
		if (incache <= target)
			break;
		items++;
		nxtcp = TAILQ_NEXT(ncp, nc_lru);
		if (ncp->nc_dvp == NULL)
			continue;
		if (ncp == sentinel) {
			/*
			 * If we looped back on ourself, then ignore
			 * recent entries and purge whatever we find.
			 */
			tryharder = 1;
		}
		if (!tryharder && ncp->nc_hittime > recent) {
			if (sentinel == NULL)
				sentinel = ncp;
			TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
			TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
			continue;
		}
		mutex_enter(&ncp->nc_lock);
		if (ncp->nc_dvp != NULL) {
			cache_invalidate(ncp);
			cache_disassociate(ncp);
			incache--;
		}
		mutex_exit(&ncp->nc_lock);
	}
	cache_ev_scan.ev_count += items;
}

/*
 * Collect dead cache entries from all CPUs and garbage collect.
 */
static void
cache_reclaim(void)
{
	struct namecache *ncp, *next;
	int items;

	KASSERT(mutex_owned(namecache_lock));

	/*
	 * If the number of extant entries not awaiting garbage collection
	 * exceeds the high water mark, then reclaim stale entries until we
	 * reach our low water mark.
	 */
	items = numcache - cache_gcpend;
	if (items > (uint64_t)desiredvnodes * cache_hiwat / 100) {
		cache_prune(items, (int)((uint64_t)desiredvnodes *
		    cache_lowat / 100));
		cache_ev_over.ev_count++;
	} else
		cache_ev_under.ev_count++;

	/*
	 * Stop forward lookup activity on all CPUs and garbage collect dead
	 * entries.
	 */
	cache_lock_cpus();
	ncp = cache_gcqueue;
	cache_gcqueue = NULL;
	items = cache_gcpend;
	cache_gcpend = 0;
	while (ncp != NULL) {
		next = ncp->nc_gcqueue;
		cache_disassociate(ncp);
		KASSERT(ncp->nc_dvp == NULL);
		if (ncp->nc_hash.le_prev != NULL) {
			LIST_REMOVE(ncp, nc_hash);
			ncp->nc_hash.le_prev = NULL;
		}
		pool_cache_put(namecache_cache, ncp);
		ncp = next;
	}
	cache_unlock_cpus();
	numcache -= items;
	cache_ev_gc.ev_count += items;
}

/*
 * Cache maintainence thread, awakening once per second to:
 *
 * => keep number of entries below the high water mark
 * => sort pseudo-LRU list
 * => garbage collect dead entries
 */
static void
cache_thread(void *arg)
{

	mutex_enter(namecache_lock);
	for (;;) {
		cache_reclaim();
		kpause("cachegc", false, hz, namecache_lock);
	}
}

#ifdef DDB
void
namecache_print(struct vnode *vp, void (*pr)(const char *, ...))
{
	struct vnode *dvp = NULL;
	struct namecache *ncp;

	TAILQ_FOREACH(ncp, &nclruhead, nc_lru) {
		if (ncp->nc_vp == vp && ncp->nc_dvp != NULL) {
			(*pr)("name %.*s\n", ncp->nc_nlen, ncp->nc_name);
			dvp = ncp->nc_dvp;
		}
	}
	if (dvp == NULL) {
		(*pr)("name not found\n");
		return;
	}
	vp = dvp;
	TAILQ_FOREACH(ncp, &nclruhead, nc_lru) {
		if (ncp->nc_vp == vp) {
			(*pr)("parent %.*s\n", ncp->nc_nlen, ncp->nc_name);
		}
	}
}
#endif