Author: mjg
Date: Sat Oct 17 08:48:32 2020
New Revision: 366784
URL: https://svnweb.freebsd.org/changeset/base/366784
Log:
cache: remove entries before trying to add new ones, not after
Should allow positive entries to replace negative ones in case
the cache is full.
Modified:
head/sys/kern/vfs_cache.c
Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c Sat Oct 17 08:47:08 2020 (r366783)
+++ head/sys/kern/vfs_cache.c Sat Oct 17 08:48:32 2020 (r366784)
@@ -1923,8 +1923,21 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp,
/*
* Avoid blowout in namecache entries.
+ *
+ * Bugs:
+ * 1. filesystems may end up tryng to add an already existing entry
+ * (for example this can happen after a cache miss during concurrent
+ * lookup), in which case we will call cache_negative_zap_one despite
+ * not adding anything.
+ * 2. the routine may fail to free anything and no provisions are made
+ * to make it try harder (see the inside for failure modes)
+ * 3. it only ever looks at negative entries.
*/
lnumcache = atomic_fetchadd_long(&numcache, 1) + 1;
+ if (numneg * ncnegfactor > lnumcache) {
+ cache_negative_zap_one();
+ lnumcache = atomic_load_long(&numcache);
+ }
if (__predict_false(lnumcache >= ncsize)) {
atomic_subtract_long(&numcache, 1);
counter_u64_add(numdrops, 1);
@@ -2087,8 +2100,6 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp,
atomic_store_char(&ncp->nc_flag, ncp->nc_flag & ~NCF_WIP);
cache_enter_unlock(&cel);
- if (numneg * ncnegfactor > lnumcache)
- cache_negative_zap_one();
if (ndd != NULL)
cache_free(ndd);
return;
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