Date: Fri, 6 Oct 2017 23:05:56 +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: r324378 - head/sys/kern Message-ID: <201710062305.v96N5uO3015851@repo.freebsd.org>
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Author: mjg Date: Fri Oct 6 23:05:55 2017 New Revision: 324378 URL: https://svnweb.freebsd.org/changeset/base/324378 Log: namecache: factor out ~MAKEENTRY lookups from the common path Lookups of the sort are rare compared to regular ones and succesfull ones result in removing entries from the cache. In the current code buckets are rlocked and a trylock dance is performed, which can fail and cause a restart. Fixing it will require a little bit of surgery and in order to keep the code maintaineable the 2 cases have to split. MFC after: 1 week Modified: head/sys/kern/vfs_cache.c Modified: head/sys/kern/vfs_cache.c ============================================================================== --- head/sys/kern/vfs_cache.c Fri Oct 6 21:52:28 2017 (r324377) +++ head/sys/kern/vfs_cache.c Fri Oct 6 23:05:55 2017 (r324378) @@ -1058,7 +1058,6 @@ cache_lookup_unlock(struct rwlock *blp, struct mtx *vl if (blp != NULL) { rw_runlock(blp); - mtx_assert(vlp, MA_NOTOWNED); } else { mtx_unlock(vlp); } @@ -1117,6 +1116,82 @@ cache_lookup_dot(struct vnode *dvp, struct vnode **vpp * not recursively acquired. */ +static __noinline int +cache_lookup_nomakeentry(struct vnode *dvp, struct vnode **vpp, + struct componentname *cnp, struct timespec *tsp, int *ticksp) +{ + struct namecache *ncp; + struct rwlock *blp; + struct mtx *dvlp, *dvlp2; + uint32_t hash; + int error; + + if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') { + counter_u64_add(dotdothits, 1); + dvlp = VP2VNODELOCK(dvp); + dvlp2 = NULL; + mtx_lock(dvlp); +retry_dotdot: + ncp = dvp->v_cache_dd; + if (ncp == NULL) { + SDT_PROBE3(vfs, namecache, lookup, miss, dvp, + "..", NULL); + mtx_unlock(dvlp); + return (0); + } + if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) { + if (ncp->nc_dvp != dvp) + panic("dvp %p v_cache_dd %p\n", dvp, ncp); + if (!cache_zap_locked_vnode_kl2(ncp, + dvp, &dvlp2)) + goto retry_dotdot; + MPASS(dvp->v_cache_dd == NULL); + mtx_unlock(dvlp); + if (dvlp2 != NULL) + mtx_unlock(dvlp2); + cache_free(ncp); + } else { + dvp->v_cache_dd = NULL; + mtx_unlock(dvlp); + if (dvlp2 != NULL) + mtx_unlock(dvlp2); + } + return (0); + } + + hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp); + blp = HASH2BUCKETLOCK(hash); +retry: + rw_rlock(blp); + + LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) { + counter_u64_add(numchecks, 1); + if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen && + !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen)) + break; + } + + /* We failed to find an entry */ + if (ncp == NULL) { + rw_runlock(blp); + SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr, + NULL); + counter_u64_add(nummisszap, 1); + return (0); + } + + counter_u64_add(numposzaps, 1); + + error = cache_zap_rlocked_bucket(ncp, blp); + if (error != 0) { + zap_and_exit_bucket_fail++; + cache_maybe_yield(); + goto retry; + } + cache_free(ncp); + return (0); +} + int cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp, struct timespec *tsp, int *ticksp) @@ -1132,69 +1207,51 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, st cnp->cn_flags &= ~MAKEENTRY; return (0); } + + counter_u64_add(numcalls, 1); + + if (__predict_false(cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.')) + return (cache_lookup_dot(dvp, vpp, cnp, tsp, ticksp)); + + if ((cnp->cn_flags & MAKEENTRY) == 0) + return (cache_lookup_nomakeentry(dvp, vpp, cnp, tsp, ticksp)); + retry: blp = NULL; - dvlp = VP2VNODELOCK(dvp); error = 0; - counter_u64_add(numcalls, 1); - - if (cnp->cn_nameptr[0] == '.') { - if (cnp->cn_namelen == 1) - return (cache_lookup_dot(dvp, vpp, cnp, tsp, ticksp)); - if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') { - counter_u64_add(dotdothits, 1); - dvlp2 = NULL; - mtx_lock(dvlp); -retry_dotdot: - ncp = dvp->v_cache_dd; - if (ncp == NULL) { - SDT_PROBE3(vfs, namecache, lookup, miss, dvp, - "..", NULL); - mtx_unlock(dvlp); - return (0); - } - if ((cnp->cn_flags & MAKEENTRY) == 0) { - if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) { - if (ncp->nc_dvp != dvp) - panic("dvp %p v_cache_dd %p\n", dvp, ncp); - if (!cache_zap_locked_vnode_kl2(ncp, - dvp, &dvlp2)) - goto retry_dotdot; - MPASS(dvp->v_cache_dd == NULL); - mtx_unlock(dvlp); - if (dvlp2 != NULL) - mtx_unlock(dvlp2); - cache_free(ncp); - } else { - dvp->v_cache_dd = NULL; - mtx_unlock(dvlp); - if (dvlp2 != NULL) - mtx_unlock(dvlp2); - } - return (0); - } - if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) { - if (ncp->nc_flag & NCF_NEGATIVE) - *vpp = NULL; - else - *vpp = ncp->nc_vp; - } else - *vpp = ncp->nc_dvp; - /* Return failure if negative entry was found. */ - if (*vpp == NULL) - goto negative_success; - CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..", - dvp, cnp->cn_nameptr, *vpp); - SDT_PROBE3(vfs, namecache, lookup, hit, dvp, "..", - *vpp); - cache_out_ts(ncp, tsp, ticksp); - if ((ncp->nc_flag & (NCF_ISDOTDOT | NCF_DTS)) == - NCF_DTS && tsp != NULL) { - ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc); - *tsp = ncp_ts->nc_dotdottime; - } - goto success; + if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') { + counter_u64_add(dotdothits, 1); + dvlp = VP2VNODELOCK(dvp); + dvlp2 = NULL; + mtx_lock(dvlp); + ncp = dvp->v_cache_dd; + if (ncp == NULL) { + SDT_PROBE3(vfs, namecache, lookup, miss, dvp, + "..", NULL); + mtx_unlock(dvlp); + return (0); } + if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) { + if (ncp->nc_flag & NCF_NEGATIVE) + *vpp = NULL; + else + *vpp = ncp->nc_vp; + } else + *vpp = ncp->nc_dvp; + /* Return failure if negative entry was found. */ + if (*vpp == NULL) + goto negative_success; + CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..", + dvp, cnp->cn_nameptr, *vpp); + SDT_PROBE3(vfs, namecache, lookup, hit, dvp, "..", + *vpp); + cache_out_ts(ncp, tsp, ticksp); + if ((ncp->nc_flag & (NCF_ISDOTDOT | NCF_DTS)) == + NCF_DTS && tsp != NULL) { + ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc); + *tsp = ncp_ts->nc_dotdottime; + } + goto success; } hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp); @@ -1210,21 +1267,11 @@ retry_dotdot: /* We failed to find an entry */ if (ncp == NULL) { + rw_runlock(blp); SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr, NULL); - if ((cnp->cn_flags & MAKEENTRY) == 0) { - counter_u64_add(nummisszap, 1); - } else { - counter_u64_add(nummiss, 1); - } - cache_lookup_unlock(blp, dvlp); + counter_u64_add(nummiss, 1); return (0); - } - - /* We don't want to have an entry, so dump it */ - if ((cnp->cn_flags & MAKEENTRY) == 0) { - counter_u64_add(numposzaps, 1); - goto zap_and_exit; } /* We found a "positive" match, return the vnode */
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