Author: mjg
Date: Wed Nov 27 01:21:42 2019
New Revision: 355125
URL: https://svnweb.freebsd.org/changeset/base/355125
Log:
cache: stop reusing .. entries on enter
It almost never happens in practice anyway. With this eliminated ->nc_vp
cannot change vnodes, removing an obstacle on the road to lockless
lookup.
Modified:
head/sys/kern/vfs_cache.c
Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c Wed Nov 27 01:20:55 2019 (r355124)
+++ head/sys/kern/vfs_cache.c Wed Nov 27 01:21:42 2019 (r355125)
@@ -1661,6 +1661,33 @@ cache_enter_unlock(struct celockstate *cel)
cache_unlock_vnodes_cel(cel);
}
+static void __noinline
+cache_enter_dotdot_prep(struct vnode *dvp, struct vnode *vp,
+ struct componentname *cnp)
+{
+ struct celockstate cel;
+ struct namecache *ncp;
+ uint32_t hash;
+ int len;
+
+ if (dvp->v_cache_dd == NULL)
+ return;
+ len = cnp->cn_namelen;
+ cache_celockstate_init(&cel);
+ hash = cache_get_hash(cnp->cn_nameptr, len, dvp);
+ cache_enter_lock_dd(&cel, dvp, vp, hash);
+ ncp = dvp->v_cache_dd;
+ if (ncp != NULL && (ncp->nc_flag & NCF_ISDOTDOT)) {
+ KASSERT(ncp->nc_dvp == dvp, ("wrong isdotdot parent"));
+ cache_zap_locked(ncp, false);
+ } else {
+ ncp = NULL;
+ }
+ dvp->v_cache_dd = NULL;
+ cache_enter_unlock(&cel);
+ cache_free(ncp);
+}
+
/*
* Add an entry to the cache.
*/
@@ -1672,11 +1699,10 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp,
struct namecache *ncp, *n2, *ndd;
struct namecache_ts *ncp_ts, *n2_ts;
struct nchashhead *ncpp;
- struct neglist *neglist;
uint32_t hash;
int flag;
int len;
- bool neg_locked, held_dvp;
+ bool held_dvp;
u_long lnumcache;
CTR3(KTR_VFS, "cache_enter(%p, %p, %s)", dvp, vp, cnp->cn_nameptr);
@@ -1690,65 +1716,12 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp,
return;
#endif
- cache_celockstate_init(&cel);
- ndd = NULL;
- ncp_ts = NULL;
flag = 0;
- if (cnp->cn_nameptr[0] == '.') {
+ if (__predict_false(cnp->cn_nameptr[0] == '.')) {
if (cnp->cn_namelen == 1)
return;
if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
- len = cnp->cn_namelen;
- hash = cache_get_hash(cnp->cn_nameptr, len, dvp);
- cache_enter_lock_dd(&cel, dvp, vp, hash);
- /*
- * If dotdot entry already exists, just retarget it
- * to new parent vnode, otherwise continue with new
- * namecache entry allocation.
- */
- if ((ncp = dvp->v_cache_dd) != NULL &&
- ncp->nc_flag & NCF_ISDOTDOT) {
- KASSERT(ncp->nc_dvp == dvp,
- ("wrong isdotdot parent"));
- neg_locked = false;
- if (ncp->nc_flag & NCF_NEGATIVE || vp == NULL) {
- neglist = NCP2NEGLIST(ncp);
- mtx_lock(&ncneg_hot.nl_lock);
- mtx_lock(&neglist->nl_lock);
- neg_locked = true;
- }
- if (!(ncp->nc_flag & NCF_NEGATIVE)) {
- TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst,
- ncp, nc_dst);
- } else {
- cache_negative_remove(ncp, true);
- }
- if (vp != NULL) {
- TAILQ_INSERT_HEAD(&vp->v_cache_dst,
- ncp, nc_dst);
- if (ncp->nc_flag & NCF_HOTNEGATIVE)
- numhotneg--;
- ncp->nc_flag &=
~(NCF_NEGATIVE|NCF_HOTNEGATIVE);
- } else {
- if (ncp->nc_flag & NCF_HOTNEGATIVE) {
- numhotneg--;
- ncp->nc_flag &=
~(NCF_HOTNEGATIVE);
- }
- ncp->nc_flag |= NCF_NEGATIVE;
- cache_negative_insert(ncp, true);
- }
- if (neg_locked) {
- mtx_unlock(&neglist->nl_lock);
- mtx_unlock(&ncneg_hot.nl_lock);
- }
- ncp->nc_vp = vp;
- cache_enter_unlock(&cel);
- return;
- }
- dvp->v_cache_dd = NULL;
- cache_enter_unlock(&cel);
- cache_celockstate_init(&cel);
- SDT_PROBE3(vfs, namecache, enter, done, dvp, "..", vp);
+ cache_enter_dotdot_prep(dvp, vp, cnp);
flag = NCF_ISDOTDOT;
}
}
@@ -1761,6 +1734,10 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp,
atomic_add_long(&numcache, -1);
return;
}
+
+ cache_celockstate_init(&cel);
+ ndd = NULL;
+ ncp_ts = NULL;
held_dvp = false;
if (LIST_EMPTY(&dvp->v_cache_src) && flag != NCF_ISDOTDOT) {
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