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cache: stop reusing .. entries on enter

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It almost never happens in practice anyway. With this eliminated ->nc_vp
cannot change vnodes, removing an obstacle on the road to lockless
lookup.
This commit is contained in:
Mateusz Guzik 2019-11-27 01:21:42 +00:00
parent 2ac930e32c
commit 588e69e2fd
1 changed files with 34 additions and 57 deletions
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91
sys/kern/vfs_cache.c
View file

@ -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 componentname *cnp,
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, struct componentname *cnp,
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;
}
}
@ -1762,6 +1735,10 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
return;
}
cache_celockstate_init(&cel);
ndd = NULL;
ncp_ts = NULL;
held_dvp = false;
if (LIST_EMPTY(&dvp->v_cache_src) && flag != NCF_ISDOTDOT) {
vhold(dvp);