Author: mjg Date: Thu Jan 16 21:45:21 2020 New Revision: 356812 URL: https://svnweb.freebsd.org/changeset/base/356812
Log: vfs: increment numvnodes without the vnode list lock unless under pressure The vnode list lock is only needed to reclaim free vnodes or kick the vnlru thread (or to block and not miss a wake up (but note the sleep has a timeout so this would not be a correctness issue)). Try to get away without the lock by just doing an atomic increment. The lock is contended e.g., during poudriere -j 104 where about half of all acquires come from vnode allocation code. Note the entire scheme needs a rewrite, the above just reduces it's SMP impact. Reviewed by: kib Differential Revision: https://reviews.freebsd.org/D23140 Modified: head/sys/kern/vfs_subr.c Modified: head/sys/kern/vfs_subr.c ============================================================================== --- head/sys/kern/vfs_subr.c Thu Jan 16 21:43:13 2020 (r356811) +++ head/sys/kern/vfs_subr.c Thu Jan 16 21:45:21 2020 (r356812) @@ -1497,21 +1497,22 @@ vtryrecycle(struct vnode *vp) * The routine can try to free a vnode or stall for up to 1 second waiting for * vnlru to clear things up, but ultimately always performs a M_WAITOK allocation. */ -static struct vnode * -vn_alloc(struct mount *mp) +static u_long vn_alloc_cyclecount; + +static struct vnode * __noinline +vn_alloc_hard(struct mount *mp) { u_long rnumvnodes, rfreevnodes; - static u_long cyclecount; mtx_lock(&vnode_list_mtx); rnumvnodes = atomic_load_long(&numvnodes); if (rnumvnodes + 1 < desiredvnodes) { - cyclecount = 0; + vn_alloc_cyclecount = 0; goto alloc; } rfreevnodes = atomic_load_long(&freevnodes); - if (cyclecount++ >= rfreevnodes) { - cyclecount = 0; + if (vn_alloc_cyclecount++ >= rfreevnodes) { + vn_alloc_cyclecount = 0; vstir = 1; } /* @@ -1543,6 +1544,22 @@ alloc: if (vnlru_under(rnumvnodes, vlowat)) vnlru_kick(); mtx_unlock(&vnode_list_mtx); + return (uma_zalloc(vnode_zone, M_WAITOK)); +} + +static struct vnode * +vn_alloc(struct mount *mp) +{ + u_long rnumvnodes; + + if (__predict_false(vn_alloc_cyclecount != 0)) + return (vn_alloc_hard(mp)); + rnumvnodes = atomic_fetchadd_long(&numvnodes, 1) + 1; + if (__predict_false(vnlru_under(rnumvnodes, vlowat))) { + atomic_subtract_long(&numvnodes, 1); + return (vn_alloc_hard(mp)); + } + return (uma_zalloc(vnode_zone, M_WAITOK)); } _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
