Author: mjg
Date: Sun Jan 19 17:47:04 2020
New Revision: 356884
URL: https://svnweb.freebsd.org/changeset/base/356884
Log:
vfs: allow v_holdcnt to transition 0->1 without the interlock
Since r356672 ("vfs: rework vnode list management") there is nothing to do
apart from altering freevnodes count, but this much can be safely done based
on the result of atomic_fetchadd.
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23186
Modified:
head/sys/kern/vfs_subr.c
Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c Sun Jan 19 17:05:26 2020 (r356883)
+++ head/sys/kern/vfs_subr.c Sun Jan 19 17:47:04 2020 (r356884)
@@ -2826,38 +2826,26 @@ v_decr_devcount(struct vnode *vp)
* see doomed vnodes. If inactive processing was delayed in
* vput try to do it here.
*
- * Both holdcnt and usecount can be manipulated using atomics without holding
- * any locks except in these cases which require the vnode interlock:
- * holdcnt: 1->0 and 0->1
- * usecount: 0->1
- *
- * usecount is permitted to transition 1->0 without the interlock because
- * vnode is kept live by holdcnt.
+ * usecount is manipulated using atomics without holding any locks,
+ * except when transitioning 0->1 in which case the interlock is held.
+
+ * holdcnt is manipulated using atomics without holding any locks,
+ * except when transitioning 1->0 in which case the interlock is held.
*/
-static enum vgetstate __always_inline
-_vget_prep(struct vnode *vp, bool interlock)
+enum vgetstate
+vget_prep(struct vnode *vp)
{
enum vgetstate vs;
if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
vs = VGET_USECOUNT;
} else {
- if (interlock)
- vholdl(vp);
- else
- vhold(vp);
+ vhold(vp);
vs = VGET_HOLDCNT;
}
return (vs);
}
-enum vgetstate
-vget_prep(struct vnode *vp)
-{
-
- return (_vget_prep(vp, false));
-}
-
int
vget(struct vnode *vp, int flags, struct thread *td)
{
@@ -2865,7 +2853,7 @@ vget(struct vnode *vp, int flags, struct thread *td)
MPASS(td == curthread);
- vs = _vget_prep(vp, (flags & LK_INTERLOCK) != 0);
+ vs = vget_prep(vp);
return (vget_finish(vp, flags, vs));
}
@@ -3234,50 +3222,30 @@ vunref(struct vnode *vp)
vputx(vp, VPUTX_VUNREF);
}
-/*
- * Increase the hold count and activate if this is the first reference.
- */
-static void
-vhold_activate(struct vnode *vp)
+void
+vhold(struct vnode *vp)
{
struct vdbatch *vd;
+ int old;
- ASSERT_VI_LOCKED(vp, __func__);
- VNASSERT(vp->v_holdcnt == 0, vp,
- ("%s: wrong hold count", __func__));
- VNASSERT(vp->v_op != NULL, vp,
- ("%s: vnode already reclaimed.", __func__));
+ CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
+ old = atomic_fetchadd_int(&vp->v_holdcnt, 1);
+ VNASSERT(old >= 0, vp, ("%s: wrong hold count %d", __func__, old));
+ if (old != 0)
+ return;
critical_enter();
vd = DPCPU_PTR(vd);
vd->freevnodes--;
critical_exit();
- refcount_acquire(&vp->v_holdcnt);
}
void
-vhold(struct vnode *vp)
-{
-
- ASSERT_VI_UNLOCKED(vp, __func__);
- CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
- if (refcount_acquire_if_not_zero(&vp->v_holdcnt))
- return;
- VI_LOCK(vp);
- vholdl(vp);
- VI_UNLOCK(vp);
-}
-
-void
vholdl(struct vnode *vp)
{
ASSERT_VI_LOCKED(vp, __func__);
CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
- if (vp->v_holdcnt > 0) {
- refcount_acquire(&vp->v_holdcnt);
- return;
- }
- vhold_activate(vp);
+ vhold(vp);
}
void
@@ -3417,8 +3385,6 @@ vdrop_deactivate(struct vnode *vp)
("vdrop: returning doomed vnode"));
VNASSERT(vp->v_op != NULL, vp,
("vdrop: vnode already reclaimed."));
- VNASSERT(vp->v_holdcnt == 0, vp,
- ("vdrop: freeing when we shouldn't"));
VNASSERT((vp->v_iflag & VI_OWEINACT) == 0, vp,
("vnode with VI_OWEINACT set"));
VNASSERT((vp->v_iflag & VI_DEFINACT) == 0, vp,
@@ -3426,9 +3392,18 @@ vdrop_deactivate(struct vnode *vp)
if (vp->v_mflag & VMP_LAZYLIST) {
mp = vp->v_mount;
mtx_lock(&mp->mnt_listmtx);
- vp->v_mflag &= ~VMP_LAZYLIST;
- TAILQ_REMOVE(&mp->mnt_lazyvnodelist, vp, v_lazylist);
- mp->mnt_lazyvnodelistsize--;
+ VNASSERT(vp->v_mflag & VMP_LAZYLIST, vp, ("lost VMP_LAZYLIST"));
+ /*
+ * Don't remove the vnode from the lazy list if another thread
+ * has increased the hold count. It may have re-enqueued the
+ * vnode to the lazy list and is now responsible for its
+ * removal.
+ */
+ if (vp->v_holdcnt == 0) {
+ vp->v_mflag &= ~VMP_LAZYLIST;
+ TAILQ_REMOVE(&mp->mnt_lazyvnodelist, vp, v_lazylist);
+ mp->mnt_lazyvnodelistsize--;
+ }
mtx_unlock(&mp->mnt_listmtx);
}
vdbatch_enqueue(vp);
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