Date: Sat, 17 Oct 2020 08:48:33 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r366784 - head/sys/kern Message-ID: <202010170848.09H8mXHr063268@repo.freebsd.org>
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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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