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d8d6519c63
formula uses `& nchash'. This is very broken when nchash is a prime number instead of 1 less than a power of 2, but the Lite2 formula was merged in. Merged some cosmetic changes from Lite2, rev.1.21 and Lite1. The merge was difficult because the Lite2 code is essentially ours (phk's) except where Lite2 improved or broke it. Summary of the Lite2 changes: - in the copyright, phk's rights have been transferred to the Regents. This change should be reviewed. - nchENOENT went away; the "no" vnode is now simply 0. - comments were improved. - style was "improved". - goto instead of Fanatism (sic) was considered bad :-). - there are some small changes to support whiteouts. - new cache entries are added in more cases. More work is required near here to change the hash table size if kern.desiredvnodes is changed using sysctl. - rescanning of the hash bucket in cache_purgevfs() was removed. This change should be reviewed.
342 lines
9.7 KiB
C
342 lines
9.7 KiB
C
/*
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* Copyright (c) 1989, 1993, 1995
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Poul-Henning Kamp of the FreeBSD Project.
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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 8.5 (Berkeley) 3/22/95
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* $Id: vfs_cache.c,v 1.23 1997/02/22 09:39:31 peter 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/kernel.h>
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#include <sys/sysctl.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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#define MAXVNODEUSE 32
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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, (i.e. for a name that is known NOT to
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* exist) the vnode pointer will be NULL.
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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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#define NCHHASH(dvp, cnp) \
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(&nchashtbl[((dvp)->v_id + (cnp)->cn_hash) % nchash])
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static LIST_HEAD(nchashhead, namecache) *nchashtbl; /* Hash Table */
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static u_long nchash; /* size of hash table */
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static u_long numcache; /* number of cache entries allocated */
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static TAILQ_HEAD(, namecache) nclruhead; /* LRU chain */
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struct nchstats nchstats; /* cache effectiveness statistics */
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static int doingcache = 1; /* 1 => enable the cache */
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SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, "");
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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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/*
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* Delete an entry from its hash list and move it to the front
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* of the LRU list for immediate reuse.
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*/
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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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}
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/*
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* Move an entry that has been used to the tail of the LRU list
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* so that it will be preserved for future use.
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*/
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#define TOUCH(ncp) { \
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if (ncp->nc_lru.tqe_next != 0) { \
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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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}
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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. If the lookup
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* succeeds, the vnode is returned in *vpp, and a status of -1 is
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* returned. If the lookup determines that the name does not exist
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* (negative cacheing), a status of ENOENT is returned. If the lookup
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* 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 = NCHHASH(dvp, cnp);
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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_vp && ncp->nc_vpid != ncp->nc_vp->v_id)) {
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nchstats.ncs_falsehits++;
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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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break;
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}
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/* We failed to find an entry */
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if (ncp == 0) {
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nchstats.ncs_miss++;
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return (0);
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}
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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) {
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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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if ((*vpp)->v_usage < MAXVNODEUSE)
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(*vpp)->v_usage++;
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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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nchstats.ncs_badhits++;
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PURGE(ncp);
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return (0);
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}
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/*
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* We found a "negative" match, ENOENT notifies client of this match.
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* The nc_vpid field records whether this is a whiteout.
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*/
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nchstats.ncs_neghits++;
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TOUCH(ncp);
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cnp->cn_flags |= ncp->nc_vpid;
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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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/*
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* We allocate a new entry if we are less than the maximum
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* allowed and the one at the front of the LRU list is in use.
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* Otherwise we use the one at the front of the LRU list.
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*/
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if (numcache < desiredvnodes &&
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((ncp = nclruhead.tqh_first) == NULL ||
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ncp->nc_hash.le_prev != 0)) {
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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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/*
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* Fill in cache info, if vp is NULL this is a "negative" cache entry.
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* For negative entries, we have to record whether it is a whiteout.
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* the whiteout flag is stored in the nc_vpid field which is
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* otherwise unused.
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*/
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ncp->nc_vp = vp;
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if (vp) {
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ncp->nc_vpid = vp->v_id;
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if (vp->v_usage < MAXVNODEUSE)
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++vp->v_usage;
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} else
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ncp->nc_vpid = cnp->cn_flags & ISWHITEOUT;
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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 = NCHHASH(dvp, cnp);
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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 = phashinit(desiredvnodes, M_CACHE, &nchash);
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}
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/*
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* Invalidate 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 stale entries
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* will be purged by lookup as they get found. If the v_id wraps around, we
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* need to ditch the entire cache, to avoid confusion. No valid vnode will
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* 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 namecache *ncp;
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struct nchashhead *ncpp;
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static u_long nextvnodeid;
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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 - 1]; ncpp >= nchashtbl; ncpp--) {
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while (ncp = ncpp->lh_first)
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PURGE(ncp);
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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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* entries at the same time.
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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, *nnp;
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/* Scan hash tables for applicable entries */
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for (ncpp = &nchashtbl[nchash - 1]; ncpp >= nchashtbl; ncpp--) {
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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 (ncp->nc_dvpid != ncp->nc_dvp->v_id ||
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(ncp->nc_vp && 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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}
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}
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}
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}
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