Date: Fri, 27 Sep 2019 19:13:23 +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: r352812 - head/sys/kern Message-ID: <201909271913.x8RJDNFF046871@repo.freebsd.org>
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Author: mjg Date: Fri Sep 27 19:13:22 2019 New Revision: 352812 URL: https://svnweb.freebsd.org/changeset/base/352812 Log: cache: stop requeuing negative entries on the hot list Turns out it does not improve hit ratio, but it does come with a cost induces stemming from dirtying hit entries. Sample result: hit counts of evicted entries after 2 buildworlds before: value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@@@@@@@@@@@@@@ 180865 1 |@@@@@@@ 49150 2 |@@@ 19067 4 |@ 9825 8 |@ 7340 16 |@ 5952 32 |@ 5243 64 |@ 4446 128 | 3556 256 | 3035 512 | 1705 1024 | 1078 2048 | 365 4096 | 95 8192 | 34 16384 | 26 32768 | 23 65536 | 8 131072 | 6 262144 | 0 after: value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@@@@@@@@@@@@@@ 184004 1 |@@@@@@ 47577 2 |@@@ 19446 4 |@ 10093 8 |@ 7470 16 |@ 5544 32 |@ 5475 64 |@ 5011 128 | 3451 256 | 3002 512 | 1729 1024 | 1086 2048 | 363 4096 | 86 8192 | 26 16384 | 25 32768 | 24 65536 | 7 131072 | 5 262144 | 0 Sponsored by: The FreeBSD Foundation Modified: head/sys/kern/vfs_cache.c Modified: head/sys/kern/vfs_cache.c ============================================================================== --- head/sys/kern/vfs_cache.c Fri Sep 27 19:12:43 2019 (r352811) +++ head/sys/kern/vfs_cache.c Fri Sep 27 19:13:22 2019 (r352812) @@ -92,10 +92,10 @@ SDT_PROBE_DEFINE1(vfs, namecache, purge_negative, done SDT_PROBE_DEFINE1(vfs, namecache, purgevfs, done, "struct mount *"); SDT_PROBE_DEFINE3(vfs, namecache, zap, done, "struct vnode *", "char *", "struct vnode *"); -SDT_PROBE_DEFINE3(vfs, namecache, zap_negative, done, "struct vnode *", - "char *", "int"); -SDT_PROBE_DEFINE3(vfs, namecache, shrink_negative, done, "struct vnode *", - "char *", "int"); +SDT_PROBE_DEFINE2(vfs, namecache, zap_negative, done, "struct vnode *", + "char *"); +SDT_PROBE_DEFINE2(vfs, namecache, shrink_negative, done, "struct vnode *", + "char *"); /* * This structure describes the elements in the cache of recent @@ -109,7 +109,6 @@ struct namecache { struct vnode *nc_dvp; /* vnode of parent of name */ union { struct vnode *nu_vp; /* vnode the name refers to */ - u_int nu_neghits; /* negative entry hits */ } n_un; u_char nc_flag; /* flag bits */ u_char nc_nlen; /* length of name */ @@ -132,7 +131,6 @@ struct namecache_ts { }; #define nc_vp n_un.nu_vp -#define nc_neghits n_un.nu_neghits /* * Flags in namecache.nc_flag @@ -220,9 +218,6 @@ SYSCTL_UINT(_vfs, OID_AUTO, ncsizefactor, CTLFLAG_RW, static u_int __read_mostly ncpurgeminvnodes; SYSCTL_UINT(_vfs, OID_AUTO, ncpurgeminvnodes, CTLFLAG_RW, &ncpurgeminvnodes, 0, "Number of vnodes below which purgevfs ignores the request"); -static u_int __read_mostly ncneghitsrequeue = 8; -SYSCTL_UINT(_vfs, OID_AUTO, ncneghitsrequeue, CTLFLAG_RW, &ncneghitsrequeue, 0, - "Number of hits to requeue a negative entry in the LRU list"); static u_int __read_mostly ncsize; /* the size as computed on creation or resizing */ struct nchstats nchstats; /* cache effectiveness statistics */ @@ -676,8 +671,6 @@ SYSCTL_PROC(_debug_hashstat, OID_AUTO, nchash, CTLTYPE * * A variation of LRU scheme is used. New entries are hashed into one of * numneglists cold lists. Entries get promoted to the hot list on first hit. - * Partial LRU for the hot list is maintained by requeueing them every - * ncneghitsrequeue hits. * * The shrinker will demote hot list head and evict from the cold list in a * round-robin manner. @@ -686,28 +679,12 @@ static void cache_negative_hit(struct namecache *ncp) { struct neglist *neglist; - u_int hits; MPASS(ncp->nc_flag & NCF_NEGATIVE); - hits = atomic_fetchadd_int(&ncp->nc_neghits, 1); - if (ncp->nc_flag & NCF_HOTNEGATIVE) { - if ((hits % ncneghitsrequeue) != 0) - return; - mtx_lock(&ncneg_hot.nl_lock); - if (ncp->nc_flag & NCF_HOTNEGATIVE) { - TAILQ_REMOVE(&ncneg_hot.nl_list, ncp, nc_dst); - TAILQ_INSERT_TAIL(&ncneg_hot.nl_list, ncp, nc_dst); - mtx_unlock(&ncneg_hot.nl_lock); - return; - } - /* - * The shrinker cleared the flag and removed the entry from - * the hot list. Put it back. - */ - } else { - mtx_lock(&ncneg_hot.nl_lock); - } + if (ncp->nc_flag & NCF_HOTNEGATIVE) + return; neglist = NCP2NEGLIST(ncp); + mtx_lock(&ncneg_hot.nl_lock); mtx_lock(&neglist->nl_lock); if (!(ncp->nc_flag & NCF_HOTNEGATIVE)) { numhotneg++; @@ -851,8 +828,9 @@ cache_negative_zap_one(void) blp != NCP2BUCKETLOCK(ncp2) || !(ncp2->nc_flag & NCF_NEGATIVE)) { ncp = NULL; } else { - SDT_PROBE3(vfs, namecache, shrink_negative, done, ncp->nc_dvp, - ncp->nc_name, ncp->nc_neghits); + SDT_PROBE2(vfs, namecache, shrink_negative, done, ncp->nc_dvp, + ncp->nc_name); + cache_zap_locked(ncp, true); counter_u64_add(numneg_evicted, 1); } @@ -887,8 +865,8 @@ cache_zap_locked(struct namecache *ncp, bool neg_locke if (ncp == ncp->nc_vp->v_cache_dd) ncp->nc_vp->v_cache_dd = NULL; } else { - SDT_PROBE3(vfs, namecache, zap_negative, done, ncp->nc_dvp, - ncp->nc_name, ncp->nc_neghits); + SDT_PROBE2(vfs, namecache, zap_negative, done, ncp->nc_dvp, + ncp->nc_name); cache_negative_remove(ncp, neg_locked); } if (ncp->nc_flag & NCF_ISDOTDOT) {
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