Author: mjg Date: Thu Jan 16 21:43:13 2020 New Revision: 356811 URL: https://svnweb.freebsd.org/changeset/base/356811
Log: vfs: refcator vnode allocation Semantics are almost identical. Some code is deduplicated and there are fewer memory accesses. Reviewed by: kib, jeff Differential Revision: https://reviews.freebsd.org/D23158 Modified: head/sys/kern/vfs_subr.c Modified: head/sys/kern/vfs_subr.c ============================================================================== --- head/sys/kern/vfs_subr.c Thu Jan 16 21:38:44 2020 (r356810) +++ head/sys/kern/vfs_subr.c Thu Jan 16 21:43:13 2020 (r356811) @@ -1275,23 +1275,6 @@ vnlru_recalc(void) vlowat = vhiwat / 2; } -/* XXX some names and initialization are bad for limits and watermarks. */ -static int -vspace(void) -{ - u_long rnumvnodes, rfreevnodes; - int space; - - rnumvnodes = atomic_load_long(&numvnodes); - rfreevnodes = atomic_load_long(&freevnodes); - if (rnumvnodes > desiredvnodes) - return (0); - space = desiredvnodes - rnumvnodes; - if (freevnodes > wantfreevnodes) - space += rfreevnodes - wantfreevnodes; - return (space); -} - /* * Attempt to recycle vnodes in a context that is always safe to block. * Calling vlrurecycle() from the bowels of filesystem code has some @@ -1300,12 +1283,40 @@ vspace(void) static struct proc *vnlruproc; static int vnlruproc_sig; +static bool +vnlru_under(u_long rnumvnodes, u_long limit) +{ + u_long rfreevnodes, space; + + if (__predict_false(rnumvnodes > desiredvnodes)) + return (true); + + space = desiredvnodes - rnumvnodes; + if (space < limit) { + rfreevnodes = atomic_load_long(&freevnodes); + if (rfreevnodes > wantfreevnodes) + space += rfreevnodes - wantfreevnodes; + } + return (space < limit); +} + static void +vnlru_kick(void) +{ + + mtx_assert(&vnode_list_mtx, MA_OWNED); + if (vnlruproc_sig == 0) { + vnlruproc_sig = 1; + wakeup(vnlruproc); + } +} + +static void vnlru_proc(void) { u_long rnumvnodes, rfreevnodes, target; unsigned long onumvnodes; - int done, force, trigger, usevnodes, vsp; + int done, force, trigger, usevnodes; bool reclaim_nc_src; EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, vnlruproc, @@ -1321,8 +1332,10 @@ vnlru_proc(void) * adjusted using its sysctl, or emergency growth), first * try to reduce it by discarding from the free list. */ - if (rnumvnodes > desiredvnodes) + if (rnumvnodes > desiredvnodes) { vnlru_free_locked(rnumvnodes - desiredvnodes, NULL); + rnumvnodes = atomic_load_long(&numvnodes); + } /* * Sleep if the vnode cache is in a good state. This is * when it is not over-full and has space for about a 4% @@ -1334,8 +1347,7 @@ vnlru_proc(void) force = 1; vstir = 0; } - vsp = vspace(); - if (vsp >= vlowat && force == 0) { + if (force == 0 && !vnlru_under(rnumvnodes, vlowat)) { vnlruproc_sig = 0; wakeup(&vnlruproc_sig); msleep(vnlruproc, &vnode_list_mtx, @@ -1394,8 +1406,7 @@ vnlru_proc(void) * After becoming active to expand above low water, keep * active until above high water. */ - vsp = vspace(); - force = vsp < vhiwat; + force = vnlru_under(numvnodes, vhiwat) ? 1 : 0; } } @@ -1471,58 +1482,35 @@ vtryrecycle(struct vnode *vp) return (0); } -static void -vcheckspace(void) -{ - int vsp; - - vsp = vspace(); - if (vsp < vlowat && vnlruproc_sig == 0) { - vnlruproc_sig = 1; - wakeup(vnlruproc); - } -} - /* - * Wait if necessary for space for a new vnode. + * Allocate a new vnode. + * + * The operation never returns an error. Returning an error was disabled + * in r145385 (dated 2005) with the following comment: + * + * XXX Not all VFS_VGET/ffs_vget callers check returns. + * + * Given the age of this commit (almost 15 years at the time of writing this + * comment) restoring the ability to fail requires a significant audit of + * all codepaths. + * + * 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 int -vn_alloc_wait(int suspended) -{ - - mtx_assert(&vnode_list_mtx, MA_OWNED); - if (numvnodes >= desiredvnodes) { - if (suspended) { - /* - * The file system is being suspended. We cannot - * risk a deadlock here, so allow allocation of - * another vnode even if this would give too many. - */ - return (0); - } - if (vnlruproc_sig == 0) { - vnlruproc_sig = 1; /* avoid unnecessary wakeups */ - wakeup(vnlruproc); - } - msleep(&vnlruproc_sig, &vnode_list_mtx, PVFS, - "vlruwk", hz); - } - /* Post-adjust like the pre-adjust in getnewvnode(). */ - if (numvnodes + 1 > desiredvnodes && freevnodes > 1) - vnlru_free_locked(1, NULL); - return (numvnodes >= desiredvnodes ? ENFILE : 0); -} - static struct vnode * vn_alloc(struct mount *mp) { - static int cyclecount; - int error __unused; + u_long rnumvnodes, rfreevnodes; + static u_long cyclecount; mtx_lock(&vnode_list_mtx); - if (numvnodes < desiredvnodes) + rnumvnodes = atomic_load_long(&numvnodes); + if (rnumvnodes + 1 < desiredvnodes) { cyclecount = 0; - else if (cyclecount++ >= freevnodes) { + goto alloc; + } + rfreevnodes = atomic_load_long(&freevnodes); + if (cyclecount++ >= rfreevnodes) { cyclecount = 0; vstir = 1; } @@ -1536,22 +1524,24 @@ vn_alloc(struct mount *mp) * should be chosen so that we never wait or even reclaim from * the free list to below its target minimum. */ - if (numvnodes + 1 <= desiredvnodes) - ; - else if (freevnodes > 0) + if (rfreevnodes > 0) { vnlru_free_locked(1, NULL); - else { - error = vn_alloc_wait(mp != NULL && (mp->mnt_kern_flag & - MNTK_SUSPEND)); -#if 0 /* XXX Not all VFS_VGET/ffs_vget callers check returns. */ - if (error != 0) { - mtx_unlock(&vnode_list_mtx); - return (error); - } -#endif + goto alloc; } - vcheckspace(); - atomic_add_long(&numvnodes, 1); + if (mp == NULL || (mp->mnt_kern_flag & MNTK_SUSPEND) == 0) { + /* + * Wait for space for a new vnode. + */ + vnlru_kick(); + msleep(&vnlruproc_sig, &vnode_list_mtx, PVFS, "vlruwk", hz); + if (atomic_load_long(&numvnodes) + 1 > desiredvnodes && + atomic_load_long(&freevnodes) > 1) + vnlru_free_locked(1, NULL); + } +alloc: + rnumvnodes = atomic_fetchadd_long(&numvnodes, 1) + 1; + if (vnlru_under(rnumvnodes, vlowat)) + vnlru_kick(); mtx_unlock(&vnode_list_mtx); 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"
