svn commit: r187839 - head/sys/kern
John Baldwin
jhb at FreeBSD.org
Wed Jan 28 11:05:19 PST 2009
Author: jhb
Date: Wed Jan 28 19:05:18 2009
New Revision: 187839
URL: http://svn.freebsd.org/changeset/base/187839
Log:
Convert the global mutex protecting the directory lookup name cache from a
mutex to a reader/writer lock. Lookup operations first grab a read lock and
perform the lookup. If the operation results in a need to modify the cache,
then it tries to do an upgrade. If that fails, it drops the read lock,
obtains a write lock, and redoes the lookup.
Modified:
head/sys/kern/vfs_cache.c
Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c Wed Jan 28 18:54:56 2009 (r187838)
+++ head/sys/kern/vfs_cache.c Wed Jan 28 19:05:18 2009 (r187839)
@@ -42,9 +42,9 @@ __FBSDID("$FreeBSD$");
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mount.h>
-#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/proc.h>
+#include <sys/rwlock.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
@@ -109,11 +109,14 @@ SYSCTL_ULONG(_debug, OID_AUTO, numcachep
#endif
struct nchstats nchstats; /* cache effectiveness statistics */
-static struct mtx cache_lock;
-MTX_SYSINIT(vfscache, &cache_lock, "Name Cache", MTX_DEF);
+static struct rwlock cache_lock;
+RW_SYSINIT(vfscache, &cache_lock, "Name Cache");
-#define CACHE_LOCK() mtx_lock(&cache_lock)
-#define CACHE_UNLOCK() mtx_unlock(&cache_lock)
+#define CACHE_UPGRADE_LOCK() rw_try_upgrade(&cache_lock)
+#define CACHE_RLOCK() rw_rlock(&cache_lock)
+#define CACHE_RUNLOCK() rw_runlock(&cache_lock)
+#define CACHE_WLOCK() rw_wlock(&cache_lock)
+#define CACHE_WUNLOCK() rw_wunlock(&cache_lock)
/*
* UMA zones for the VFS cache.
@@ -162,6 +165,7 @@ static u_long numposzaps; STATNODE(CTLFL
static u_long numposhits; STATNODE(CTLFLAG_RD, numposhits, &numposhits);
static u_long numnegzaps; STATNODE(CTLFLAG_RD, numnegzaps, &numnegzaps);
static u_long numneghits; STATNODE(CTLFLAG_RD, numneghits, &numneghits);
+static u_long numupgrades; STATNODE(CTLFLAG_RD, numupgrades, &numupgrades);
SYSCTL_OPAQUE(_vfs_cache, OID_AUTO, nchstats, CTLFLAG_RD | CTLFLAG_MPSAFE,
&nchstats, sizeof(nchstats), "LU", "VFS cache effectiveness statistics");
@@ -200,12 +204,12 @@ sysctl_debug_hashstat_rawnchash(SYSCTL_H
/* Scan hash tables for applicable entries */
for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
- CACHE_LOCK();
+ CACHE_RLOCK();
count = 0;
LIST_FOREACH(ncp, ncpp, nc_hash) {
count++;
}
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
error = SYSCTL_OUT(req, &count, sizeof(count));
if (error)
return (error);
@@ -235,11 +239,11 @@ sysctl_debug_hashstat_nchash(SYSCTL_HAND
/* Scan hash tables for applicable entries */
for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
count = 0;
- CACHE_LOCK();
+ CACHE_RLOCK();
LIST_FOREACH(ncp, ncpp, nc_hash) {
count++;
}
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
if (count)
used++;
if (maxlength < count)
@@ -277,7 +281,7 @@ cache_zap(ncp)
{
struct vnode *vp;
- mtx_assert(&cache_lock, MA_OWNED);
+ rw_assert(&cache_lock, RA_WLOCKED);
CTR2(KTR_VFS, "cache_zap(%p) vp %p", ncp, ncp->nc_vp);
vp = NULL;
LIST_REMOVE(ncp, nc_hash);
@@ -324,16 +328,19 @@ cache_lookup(dvp, vpp, cnp)
{
struct namecache *ncp;
u_int32_t hash;
- int error, ltype;
+ int error, ltype, wlocked;
if (!doingcache) {
cnp->cn_flags &= ~MAKEENTRY;
return (0);
}
retry:
- CACHE_LOCK();
+ CACHE_RLOCK();
+ wlocked = 0;
numcalls++;
+ error = 0;
+retry_wlocked:
if (cnp->cn_nameptr[0] == '.') {
if (cnp->cn_namelen == 1) {
*vpp = dvp;
@@ -346,8 +353,7 @@ retry:
dotdothits++;
if (dvp->v_dd == NULL ||
(cnp->cn_flags & MAKEENTRY) == 0) {
- CACHE_UNLOCK();
- return (0);
+ goto unlock;
}
*vpp = dvp->v_dd;
CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..",
@@ -366,23 +372,24 @@ retry:
}
/* We failed to find an entry */
- if (ncp == 0) {
+ if (ncp == NULL) {
if ((cnp->cn_flags & MAKEENTRY) == 0) {
nummisszap++;
} else {
nummiss++;
}
nchstats.ncs_miss++;
- CACHE_UNLOCK();
- return (0);
+ goto unlock;
}
/* We don't want to have an entry, so dump it */
if ((cnp->cn_flags & MAKEENTRY) == 0) {
numposzaps++;
nchstats.ncs_badhits++;
+ if (!wlocked && !CACHE_UPGRADE_LOCK())
+ goto wlock;
cache_zap(ncp);
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
return (0);
}
@@ -400,11 +407,15 @@ retry:
if (cnp->cn_nameiop == CREATE) {
numnegzaps++;
nchstats.ncs_badhits++;
+ if (!wlocked && !CACHE_UPGRADE_LOCK())
+ goto wlock;
cache_zap(ncp);
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
return (0);
}
+ if (!wlocked && !CACHE_UPGRADE_LOCK())
+ goto wlock;
numneghits++;
/*
* We found a "negative" match, so we shift it to the end of
@@ -417,9 +428,20 @@ retry:
nchstats.ncs_neghits++;
if (ncp->nc_flag & NCF_WHITE)
cnp->cn_flags |= ISWHITEOUT;
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
return (ENOENT);
+wlock:
+ /*
+ * We need to update the cache after our lookup, so upgrade to
+ * a write lock and retry the operation.
+ */
+ CACHE_RUNLOCK();
+ CACHE_WLOCK();
+ numupgrades++;
+ wlocked = 1;
+ goto retry_wlocked;
+
success:
/*
* On success we return a locked and ref'd vnode as per the lookup
@@ -427,7 +449,10 @@ success:
*/
if (dvp == *vpp) { /* lookup on "." */
VREF(*vpp);
- CACHE_UNLOCK();
+ if (wlocked)
+ CACHE_WUNLOCK();
+ else
+ CACHE_RUNLOCK();
/*
* When we lookup "." we still can be asked to lock it
* differently...
@@ -453,7 +478,10 @@ success:
VOP_UNLOCK(dvp, 0);
}
VI_LOCK(*vpp);
- CACHE_UNLOCK();
+ if (wlocked)
+ CACHE_WUNLOCK();
+ else
+ CACHE_RUNLOCK();
error = vget(*vpp, cnp->cn_lkflags | LK_INTERLOCK, cnp->cn_thread);
if (cnp->cn_flags & ISDOTDOT)
vn_lock(dvp, ltype | LK_RETRY);
@@ -466,6 +494,13 @@ success:
ASSERT_VOP_ELOCKED(*vpp, "cache_lookup");
}
return (-1);
+
+unlock:
+ if (wlocked)
+ CACHE_WUNLOCK();
+ else
+ CACHE_RUNLOCK();
+ return (0);
}
/*
@@ -509,10 +544,10 @@ cache_enter(dvp, vp, cnp)
* cache_purge() time.
*/
if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
- CACHE_LOCK();
+ CACHE_WLOCK();
if (!TAILQ_EMPTY(&dvp->v_cache_dst))
dvp->v_dd = vp;
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
return;
}
}
@@ -531,7 +566,7 @@ cache_enter(dvp, vp, cnp)
hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT);
bcopy(cnp->cn_nameptr, ncp->nc_name, len);
hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
- CACHE_LOCK();
+ CACHE_WLOCK();
/*
* See if this vnode or negative entry is already in the cache
@@ -543,7 +578,7 @@ cache_enter(dvp, vp, cnp)
if (n2->nc_dvp == dvp &&
n2->nc_nlen == cnp->cn_namelen &&
!bcmp(n2->nc_name, cnp->cn_nameptr, n2->nc_nlen)) {
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
cache_free(ncp);
return;
}
@@ -587,7 +622,7 @@ cache_enter(dvp, vp, cnp)
vhold(dvp);
if (zap)
cache_zap(ncp);
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
}
/*
@@ -618,13 +653,13 @@ cache_purge(vp)
{
CTR1(KTR_VFS, "cache_purge(%p)", vp);
- CACHE_LOCK();
+ CACHE_WLOCK();
while (!LIST_EMPTY(&vp->v_cache_src))
cache_zap(LIST_FIRST(&vp->v_cache_src));
while (!TAILQ_EMPTY(&vp->v_cache_dst))
cache_zap(TAILQ_FIRST(&vp->v_cache_dst));
vp->v_dd = NULL;
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
}
/*
@@ -638,14 +673,14 @@ cache_purgevfs(mp)
struct namecache *ncp, *nnp;
/* Scan hash tables for applicable entries */
- CACHE_LOCK();
+ CACHE_WLOCK();
for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
LIST_FOREACH_SAFE(ncp, ncpp, nc_hash, nnp) {
if (ncp->nc_dvp->v_mount == mp)
cache_zap(ncp);
}
}
- CACHE_UNLOCK();
+ CACHE_WUNLOCK();
}
/*
@@ -845,7 +880,7 @@ vn_vptocnp(struct vnode **vp, char **bp,
int error, vfslocked;
vhold(*vp);
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
vfslocked = VFS_LOCK_GIANT((*vp)->v_mount);
vn_lock(*vp, LK_SHARED | LK_RETRY);
error = VOP_VPTOCNP(*vp, &dvp, buf, buflen);
@@ -858,10 +893,10 @@ vn_vptocnp(struct vnode **vp, char **bp,
}
*bp = buf + *buflen;
*vp = dvp;
- CACHE_LOCK();
+ CACHE_RLOCK();
if ((*vp)->v_iflag & VI_DOOMED) {
/* forced unmount */
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
vdrop(*vp);
return (ENOENT);
}
@@ -887,7 +922,7 @@ vn_fullpath1(struct thread *td, struct v
error = 0;
slash_prefixed = 0;
- CACHE_LOCK();
+ CACHE_RLOCK();
numfullpathcalls++;
if (vp->v_type != VDIR) {
ncp = TAILQ_FIRST(&vp->v_cache_dst);
@@ -896,7 +931,7 @@ vn_fullpath1(struct thread *td, struct v
*--bp = ncp->nc_name[i];
if (bp == buf) {
numfullpathfail4++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
return (ENOMEM);
}
vp = ncp->nc_dvp;
@@ -910,7 +945,7 @@ vn_fullpath1(struct thread *td, struct v
buflen--;
if (buflen < 0) {
numfullpathfail4++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
return (ENOMEM);
}
slash_prefixed = 1;
@@ -918,7 +953,7 @@ vn_fullpath1(struct thread *td, struct v
while (vp != rdir && vp != rootvnode) {
if (vp->v_vflag & VV_ROOT) {
if (vp->v_iflag & VI_DOOMED) { /* forced unmount */
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
error = EBADF;
break;
}
@@ -927,7 +962,7 @@ vn_fullpath1(struct thread *td, struct v
}
if (vp->v_type != VDIR) {
numfullpathfail1++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
error = ENOTDIR;
break;
}
@@ -939,7 +974,7 @@ vn_fullpath1(struct thread *td, struct v
*--bp = ncp->nc_name[i];
if (bp == buf) {
numfullpathfail4++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
error = ENOMEM;
break;
}
@@ -954,7 +989,7 @@ vn_fullpath1(struct thread *td, struct v
buflen--;
if (buflen < 0) {
numfullpathfail4++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
error = ENOMEM;
break;
}
@@ -965,14 +1000,14 @@ vn_fullpath1(struct thread *td, struct v
if (!slash_prefixed) {
if (bp == buf) {
numfullpathfail4++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
return (ENOMEM);
} else {
*--bp = '/';
}
}
numfullpathfound++;
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
*retbuf = bp;
return (0);
@@ -984,15 +1019,15 @@ vn_commname(struct vnode *vp, char *buf,
struct namecache *ncp;
int l;
- CACHE_LOCK();
+ CACHE_RLOCK();
ncp = TAILQ_FIRST(&vp->v_cache_dst);
if (!ncp) {
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
return (ENOENT);
}
l = min(ncp->nc_nlen, buflen - 1);
memcpy(buf, ncp->nc_name, l);
- CACHE_UNLOCK();
+ CACHE_RUNLOCK();
buf[l] = '\0';
return (0);
}
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