Author: mjg
Date: Sat Oct 17 13:04:25 2020
New Revision: 366791
URL: https://svnweb.freebsd.org/changeset/base/366791
Log:
cache: avoid smr in cache_neg_evict in favoro of the already held bucket lock
Modified:
head/sys/kern/vfs_cache.c
Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c Sat Oct 17 09:51:17 2020 (r366790)
+++ head/sys/kern/vfs_cache.c Sat Oct 17 13:04:25 2020 (r366791)
@@ -803,6 +803,11 @@ SYSCTL_COUNTER_U64(_vfs_cache_neg, OID_AUTO, evict_ski
&neg_evict_skipped_empty,
"Number of times evicting failed due to lack of entries");
+static COUNTER_U64_DEFINE_EARLY(neg_evict_skipped_missed);
+SYSCTL_COUNTER_U64(_vfs_cache_neg, OID_AUTO, evict_skipped_missed, CTLFLAG_RD,
+ &neg_evict_skipped_missed,
+ "Number of times evicting failed due to target entry disappearing");
+
static COUNTER_U64_DEFINE_EARLY(neg_evict_skipped_contended);
SYSCTL_COUNTER_U64(_vfs_cache_neg, OID_AUTO, evict_skipped_contended,
CTLFLAG_RD,
&neg_evict_skipped_contended,
@@ -1008,8 +1013,11 @@ cache_neg_evict(void)
struct namecache *ncp, *ncp2;
struct neglist *nl;
struct negstate *ns;
+ struct vnode *dvp;
struct mtx *dvlp;
struct mtx *blp;
+ uint32_t hash;
+ u_char nlen;
nl = cache_neg_evict_select();
if (nl == NULL) {
@@ -1033,25 +1041,30 @@ cache_neg_evict(void)
return;
}
ns = NCP2NEGSTATE(ncp);
- dvlp = VP2VNODELOCK(ncp->nc_dvp);
- blp = NCP2BUCKETLOCK(ncp);
+ nlen = ncp->nc_nlen;
+ dvp = ncp->nc_dvp;
+ hash = cache_get_hash(ncp->nc_name, nlen, dvp);
+ dvlp = VP2VNODELOCK(dvp);
+ blp = HASH2BUCKETLOCK(hash);
mtx_unlock(&nl->nl_lock);
mtx_unlock(&nl->nl_evict_lock);
mtx_lock(dvlp);
mtx_lock(blp);
/*
- * Enter SMR to safely check the negative list.
- * Even if the found pointer matches, the entry may now be reallocated
- * and used by a different vnode.
+ * Note that since all locks were dropped above, the entry may be
+ * gone or reallocated to be something else.
*/
- vfs_smr_enter();
- ncp2 = TAILQ_FIRST(&nl->nl_list);
- if (ncp != ncp2 || dvlp != VP2VNODELOCK(ncp2->nc_dvp) ||
- blp != NCP2BUCKETLOCK(ncp2)) {
- vfs_smr_exit();
+ CK_SLIST_FOREACH(ncp2, (NCHHASH(hash)), nc_hash) {
+ if (ncp2 == ncp && ncp2->nc_dvp == dvp &&
+ ncp2->nc_nlen == nlen && (ncp2->nc_flag & NCF_NEGATIVE) !=
0)
+ break;
+ }
+ if (ncp2 == NULL) {
+ counter_u64_add(neg_evict_skipped_missed, 1);
ncp = NULL;
} else {
- vfs_smr_exit();
+ MPASS(dvlp == VP2VNODELOCK(ncp->nc_dvp));
+ MPASS(blp == NCP2BUCKETLOCK(ncp));
SDT_PROBE2(vfs, namecache, evict_negative, done, ncp->nc_dvp,
ncp->nc_name);
cache_zap_locked(ncp);
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