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[src/ad-namecache]: src/sys Make the per-directory lock a rwlock.
details: https://anonhg.NetBSD.org/src/rev/30e99cb5d2d0
branches: ad-namecache
changeset: 467092:30e99cb5d2d0
user: ad <ad%NetBSD.org@localhost>
date: Mon Jan 13 08:51:06 2020 +0000
description:
Make the per-directory lock a rwlock.
diffstat:
sys/kern/vfs_cache.c | 98 +++++++++++++++++++++++++++++----------------------
sys/sys/namei.src | 5 +-
sys/sys/vnode_impl.h | 4 +-
3 files changed, 61 insertions(+), 46 deletions(-)
diffs (truncated from 375 to 300 lines):
diff -r a7a1ba567d25 -r 30e99cb5d2d0 sys/kern/vfs_cache.c
--- a/sys/kern/vfs_cache.c Wed Jan 08 21:55:10 2020 +0000
+++ b/sys/kern/vfs_cache.c Mon Jan 13 08:51:06 2020 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: vfs_cache.c,v 1.126.2.3 2020/01/08 21:55:10 ad Exp $ */
+/* $NetBSD: vfs_cache.c,v 1.126.2.4 2020/01/13 08:51:07 ad Exp $ */
/*-
* Copyright (c) 2008, 2019 The NetBSD Foundation, Inc.
@@ -100,9 +100,10 @@
* vp->v_interlock: per vnode interlock taken when acquiring a ref.
*
* Most all modifications are made holding both cache_list_lock and the
- * directory lock. nc_hittime is modified with only the directory lock
- * held. See the definition of "struct namecache" in src/sys/namei.src
- * for the particulars.
+ * directory lock write locked. nc_hittime does not have any kind of
+ * serialization appliet to it - updates are racy, but since it's only
+ * used for pseudo-LRU replacement it doesn't matter. See definition
+ * of "struct namecache" in src/sys/namei.src for the particulars.
*
* Per-CPU statistics, and "numcache" are read unlocked, since an
* approximate value is OK. We maintain uintptr_t sized per-CPU
@@ -149,7 +150,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.126.2.3 2020/01/08 21:55:10 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.126.2.4 2020/01/13 08:51:07 ad Exp $");
#define __NAMECACHE_PRIVATE
#ifdef _KERNEL_OPT
@@ -280,7 +281,7 @@
cache_remove(struct namecache *ncp, bool inreverse)
{
- KASSERT(mutex_owned(VNODE_TO_VIMPL(ncp->nc_dvp)->vi_nclock));
+ KASSERT(rw_write_held(VNODE_TO_VIMPL(ncp->nc_dvp)->vi_nclock));
SDT_PROBE(vfs, namecache, invalidate, done, ncp->nc_dvp,
0, 0, 0, 0);
@@ -323,7 +324,7 @@
struct namecache *ncp;
struct iovec iov;
- KASSERT(mutex_owned(VNODE_TO_VIMPL(dvp)->vi_nclock));
+ KASSERT(rw_lock_held(VNODE_TO_VIMPL(dvp)->vi_nclock));
iov.iov_base = __UNCONST(name);
iov.iov_len = namelen;
@@ -333,7 +334,9 @@
KASSERT(ncp->nc_dvp == dvp);
/*
* Avoid false sharing: don't write back to nc_hittime
- * unless changed significantly.
+ * unless changed significantly. This is an unlocked
+ * update and is racy, but it doesn't matter since it's
+ * only used for pseudo-LRU replacement.
*/
if (((ncp->nc_hittime ^ hardclock_ticks) & ~31) != 0) {
ncp->nc_hittime = hardclock_ticks;
@@ -404,9 +407,10 @@
{
struct namecache *ncp;
struct vnode *vp;
- kmutex_t *dirlock;
+ krwlock_t *dirlock;
int error;
bool hit;
+ krw_t op;
/* Establish default result values */
if (iswht_ret != NULL) {
@@ -426,11 +430,19 @@
return false;
}
+ /* Could the entry be purged below? */
+ if ((cnflags & ISLASTCN) != 0 &&
+ ((cnflags & MAKEENTRY) == 0 || nameiop == CREATE)) {
+ op = RW_WRITER;
+ } else {
+ op = RW_READER;
+ }
+
dirlock = VNODE_TO_VIMPL(dvp)->vi_nclock;
- mutex_enter(dirlock);
+ rw_enter(dirlock, op);
ncp = cache_lookup_entry(dvp, name, namelen);
if (__predict_false(ncp == NULL)) {
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/* found nothing */
COUNT(ncs_miss);
return false;
@@ -442,7 +454,7 @@
* want cache entry to exist.
*/
cache_remove(ncp, false);
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/* found nothing */
COUNT(ncs_badhits);
return false;
@@ -472,12 +484,12 @@
} else {
KASSERT(!ncp->nc_whiteout);
}
- mutex_exit(dirlock);
+ rw_exit(dirlock);
return hit;
}
vp = ncp->nc_vp;
mutex_enter(vp->v_interlock);
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/*
* Unlocked except for the vnode interlock. Call vcache_tryvget().
@@ -513,7 +525,7 @@
{
struct namecache *ncp;
struct vnode *vp;
- kmutex_t *dirlock;
+ krwlock_t *dirlock;
int error;
/* Establish default results. */
@@ -528,16 +540,16 @@
}
dirlock = VNODE_TO_VIMPL(dvp)->vi_nclock;
- mutex_enter(dirlock);
+ rw_enter(dirlock, RW_READER);
if (__predict_false(namelen > USHRT_MAX)) {
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/* found nothing */
COUNT(ncs_long);
return false;
}
ncp = cache_lookup_entry(dvp, name, namelen);
if (__predict_false(ncp == NULL)) {
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/* found nothing */
COUNT(ncs_miss);
return false;
@@ -551,13 +563,13 @@
/*cnp->cn_flags |= ncp->nc_flags;*/
*iswht_ret = ncp->nc_whiteout;
}
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/* found negative entry; vn is already null from above */
COUNT(ncs_neghits);
return true;
}
mutex_enter(vp->v_interlock);
- mutex_exit(dirlock);
+ rw_exit(dirlock);
/*
* Unlocked except for the vnode interlock. Call vcache_tryvget().
@@ -672,6 +684,7 @@
struct namecache *ncp;
struct namecache *oncp;
vnode_impl_t *vi, *dvi;
+ krwlock_t *dirlock;
/* First, check whether we can/should add a cache entry. */
if ((cnflags & MAKEENTRY) == 0 ||
@@ -701,7 +714,8 @@
* cache entry. if there's a duplicated entry, free it.
*/
dvi = VNODE_TO_VIMPL(dvp);
- mutex_enter(dvi->vi_nclock);
+ dirlock = dvi->vi_nclock;
+ rw_enter(dirlock, RW_WRITER);
oncp = cache_lookup_entry(dvp, name, namelen);
if (oncp) {
cache_remove(oncp, false);
@@ -738,7 +752,7 @@
}
}
mutex_exit(&cache_list_lock);
- mutex_exit(dvi->vi_nclock);
+ rw_exit(dirlock);
}
/*
@@ -809,7 +823,7 @@
{
vnode_impl_t *vi = VNODE_TO_VIMPL(vp);
- vi->vi_nclock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);
+ vi->vi_nclock = rw_obj_alloc();
rb_tree_init(&vi->vi_nctree, &cache_rbtree_ops);
TAILQ_INIT(&vi->vi_nclist);
}
@@ -824,7 +838,7 @@
KASSERT(RB_TREE_MIN(&vi->vi_nctree) == NULL);
KASSERT(TAILQ_EMPTY(&vi->vi_nclist));
- mutex_obj_free(vi->vi_nclock);
+ rw_obj_free(vi->vi_nclock);
}
/*
@@ -835,7 +849,7 @@
cache_purge1(struct vnode *vp, const char *name, size_t namelen, int flags)
{
struct namecache *ncp;
- kmutex_t *dirlock, *blocked;
+ krwlock_t *dirlock, *blocked;
if (flags & PURGE_PARENTS) {
SDT_PROBE(vfs, namecache, purge, parents, vp, 0, 0, 0, 0);
@@ -854,13 +868,13 @@
* in a row, we'll give the other side a breather to
* prevent livelock.
*/
- if (!mutex_tryenter(dirlock)) {
- mutex_obj_hold(dirlock);
+ if (!rw_tryenter(dirlock, RW_WRITER)) {
+ rw_obj_hold(dirlock);
mutex_exit(&cache_list_lock);
- mutex_enter(dirlock);
+ rw_enter(dirlock, RW_WRITER);
/* Do nothing. */
- mutex_exit(dirlock);
- mutex_obj_free(dirlock);
+ rw_exit(dirlock);
+ rw_obj_free(dirlock);
if (blocked == dirlock) {
kpause("livelock", false, 1, NULL);
}
@@ -868,7 +882,7 @@
blocked = dirlock;
} else {
cache_remove(ncp, true);
- mutex_exit(dirlock);
+ rw_exit(dirlock);
blocked = NULL;
}
}
@@ -877,22 +891,22 @@
if (flags & PURGE_CHILDREN) {
SDT_PROBE(vfs, namecache, purge, children, vp, 0, 0, 0, 0);
dirlock = VNODE_TO_VIMPL(vp)->vi_nclock;
- mutex_enter(dirlock);
+ rw_enter(dirlock, RW_WRITER);
while ((ncp = rb_tree_iterate(&VNODE_TO_VIMPL(vp)->vi_nctree,
NULL, RB_DIR_RIGHT)) != NULL) {
cache_remove(ncp, false);
}
- mutex_exit(dirlock);
+ rw_exit(dirlock);
}
if (name != NULL) {
SDT_PROBE(vfs, namecache, purge, name, name, namelen, 0, 0, 0);
dirlock = VNODE_TO_VIMPL(vp)->vi_nclock;
- mutex_enter(dirlock);
+ rw_enter(dirlock, RW_WRITER);
ncp = cache_lookup_entry(vp, name, namelen);
if (ncp) {
cache_remove(ncp, false);
}
- mutex_exit(dirlock);
+ rw_exit(dirlock);
}
}
@@ -906,7 +920,7 @@
struct vnode_iterator *marker;
struct namecache *ncp;
vnode_impl_t *vi;
- kmutex_t *dirlock;
+ krwlock_t *dirlock;
vnode_t *vp;
/*
@@ -923,12 +937,12 @@
continue;
}
dirlock = vi->vi_nclock;
- mutex_enter(dirlock);
+ rw_enter(dirlock, RW_WRITER);
while ((ncp = rb_tree_iterate(&vi->vi_nctree, NULL,
RB_DIR_RIGHT)) != NULL) {
cache_remove(ncp, false);
}
- mutex_exit(dirlock);
+ rw_exit(dirlock);
}
vfs_vnode_iterator_destroy(marker);
}
@@ -945,7 +959,7 @@
cache_reclaim(void)
{
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