b2e10d6d6f
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
311 lines
8.6 KiB
C
311 lines
8.6 KiB
C
/*
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* Copyright (c) 1989, 1993
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* The Regents of the University of California. All rights reserved.
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* Copyright (c) 1995
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* Poul-Henning Kamp. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)vfs_cache.c 8.3 (Berkeley) 8/22/94
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* $Id: vfs_cache.c,v 1.7 1995/03/08 01:40:44 phk Exp $
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/time.h>
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#include <sys/mount.h>
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#include <sys/vnode.h>
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#include <sys/namei.h>
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#include <sys/errno.h>
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#include <sys/malloc.h>
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/*
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* Name caching works as follows:
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*
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* Names found by directory scans are retained in a cache
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* for future reference. It is managed LRU, so frequently
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* used names will hang around. Cache is indexed by hash value
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* obtained from (vp, name) where vp refers to the directory
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* containing name.
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*
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* If it is a "negative" entry, (that we know a name to >not< exist)
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* we point out entry at our own "nchENOENT", to avoid too much special
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* casing in the inner loops of lookup.
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*
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* For simplicity (and economy of storage), names longer than
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* a maximum length of NCHNAMLEN are not cached; they occur
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* infrequently in any case, and are almost never of interest.
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*
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* Upon reaching the last segment of a path, if the reference
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* is for DELETE, or NOCACHE is set (rewrite), and the
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* name is located in the cache, it will be dropped.
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*/
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/*
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* Structures associated with name cacheing.
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*/
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LIST_HEAD(nchashhead, namecache) *nchashtbl; /* Hash Table */
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TAILQ_HEAD(, namecache) nclruhead; /* LRU chain */
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u_long nchash; /* size of hash table - 1 */
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struct nchstats nchstats; /* cache effectiveness statistics */
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struct vnode nchENOENT; /* our own "novnode" */
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int doingcache = 1; /* 1 => enable the cache */
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#ifdef NCH_STATISTICS
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u_long nchnbr;
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#define NCHNBR(ncp) (ncp)->nc_nbr = ++nchnbr;
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#define NCHHIT(ncp) (ncp)->nc_hits++
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#else
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#define NCHNBR(ncp)
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#define NCHHIT(ncp)
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#endif
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#define PURGE(ncp) { \
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LIST_REMOVE(ncp, nc_hash); \
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ncp->nc_hash.le_prev = 0; \
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TAILQ_REMOVE(&nclruhead, ncp, nc_lru); \
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TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru); }
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#define TOUCH(ncp) { \
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if (ncp->nc_lru.tqe_next == 0) { } else { \
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TAILQ_REMOVE(&nclruhead, ncp, nc_lru); \
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TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru); \
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NCHNBR(ncp); } }
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/*
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* Lookup an entry in the cache
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*
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* We don't do this if the segment name is long, simply so the cache
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* can avoid holding long names (which would either waste space, or
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* add greatly to the complexity).
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*
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* Lookup is called with dvp pointing to the directory to search,
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* cnp pointing to the name of the entry being sought.
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* If the lookup succeeds, the vnode is returned in *vpp, and a status
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* of -1 is returned.
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* If the lookup determines that the name does not exist (negative cacheing),
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* a status of ENOENT is returned.
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* If the lookup fails, a status of zero is returned.
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*/
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int
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cache_lookup(dvp, vpp, cnp)
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struct vnode *dvp;
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struct vnode **vpp;
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struct componentname *cnp;
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{
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register struct namecache *ncp,*nnp;
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register struct nchashhead *ncpp;
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if (!doingcache) {
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cnp->cn_flags &= ~MAKEENTRY;
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return (0);
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}
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if (cnp->cn_namelen > NCHNAMLEN) {
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nchstats.ncs_long++;
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cnp->cn_flags &= ~MAKEENTRY;
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return (0);
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}
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ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) & nchash];
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for (ncp = ncpp->lh_first; ncp != 0; ncp = nnp) {
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nnp = ncp->nc_hash.le_next;
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/* If one of the vp's went stale, don't bother anymore. */
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if ((ncp->nc_dvpid != ncp->nc_dvp->v_id) ||
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(ncp->nc_vpid != ncp->nc_vp->v_id)) {
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PURGE(ncp);
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continue;
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}
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/* Now that we know the vp's to be valid, is it ours ? */
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if (ncp->nc_dvp == dvp &&
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ncp->nc_nlen == cnp->cn_namelen &&
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!bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
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goto found; /* Fanatism considered bad. */
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}
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nchstats.ncs_miss++;
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return (0);
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found:
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NCHHIT(ncp);
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/* We don't want to have an entry, so dump it */
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if ((cnp->cn_flags & MAKEENTRY) == 0) {
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nchstats.ncs_badhits++;
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PURGE(ncp);
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return (0);
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}
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/* We found a "positive" match, return the vnode */
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if (ncp->nc_vp != &nchENOENT) {
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nchstats.ncs_goodhits++;
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TOUCH(ncp);
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*vpp = ncp->nc_vp;
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return (-1);
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}
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/* We found a negative match, and want to create it, so purge */
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if (cnp->cn_nameiop == CREATE) {
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PURGE(ncp);
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return (0);
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}
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/* The name does not exists */
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nchstats.ncs_neghits++;
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TOUCH(ncp);
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return (ENOENT);
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}
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/*
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* Add an entry to the cache.
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*/
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void
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cache_enter(dvp, vp, cnp)
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struct vnode *dvp;
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struct vnode *vp;
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struct componentname *cnp;
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{
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register struct namecache *ncp;
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register struct nchashhead *ncpp;
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if (!doingcache)
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return;
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if (cnp->cn_namelen > NCHNAMLEN) {
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printf("cache_enter: name too long");
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return;
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}
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if (numcache < numvnodes) {
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/* Add one more entry */
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ncp = (struct namecache *)
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malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
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bzero((char *)ncp, sizeof *ncp);
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numcache++;
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} else if (ncp = nclruhead.tqh_first) {
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/* reuse an old entry */
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TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
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if (ncp->nc_hash.le_prev != 0) {
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LIST_REMOVE(ncp, nc_hash);
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ncp->nc_hash.le_prev = 0;
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}
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} else {
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/* give up */
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return;
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}
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/* If vp is NULL this is a "negative" cache entry */
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if (!vp)
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vp = &nchENOENT;
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/* fill in cache info */
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ncp->nc_vp = vp;
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ncp->nc_vpid = vp->v_id;
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ncp->nc_dvp = dvp;
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ncp->nc_dvpid = dvp->v_id;
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ncp->nc_nlen = cnp->cn_namelen;
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bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen);
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TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
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ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) & nchash];
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LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
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}
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/*
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* Name cache initialization, from vfs_init() when we are booting
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*/
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void
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nchinit()
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{
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TAILQ_INIT(&nclruhead);
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nchashtbl = hashinit(desiredvnodes, M_CACHE, &nchash);
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nchENOENT.v_id = 1;
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}
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/*
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* Invalidate a all entries to particular vnode.
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*
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* We actually just increment the v_id, that will do it. The entries will
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* be purged by lookup as they get found.
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* If the v_id wraps around, we need to ditch the entire cache, to avoid
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* confusion.
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* No valid vnode will ever have (v_id == 0).
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*/
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void
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cache_purge(vp)
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struct vnode *vp;
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{
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struct nchashhead *ncpp;
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vp->v_id = ++nextvnodeid;
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if (nextvnodeid != 0)
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return;
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for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
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while(ncpp->lh_first)
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PURGE(ncpp->lh_first);
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}
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vp->v_id = ++nextvnodeid;
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}
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/*
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* Flush all entries referencing a particular filesystem.
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*
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* Since we need to check it anyway, we will flush all the invalid
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* entriess at the same time.
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*
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* If we purge anything, we scan the hash-bucket again. There is only
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* a handful of entries, so it cheap and simple.
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*/
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void
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cache_purgevfs(mp)
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struct mount *mp;
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{
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struct nchashhead *ncpp;
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struct namecache *ncp, *nxtcp;
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/* Scan hash tables for applicable entries */
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for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
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ncp = ncpp->lh_first;
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while(ncp) {
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if (ncp->nc_dvpid != ncp->nc_dvp->v_id ||
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ncp->nc_vpid != ncp->nc_vp->v_id ||
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ncp->nc_dvp->v_mount == mp) {
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PURGE(ncp);
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ncp = ncpp->lh_first;
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} else {
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ncp = ncp->nc_lru.tqe_next;
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}
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}
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}
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}
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