svn commit: r354890 - in head/sys: fs/devfs kern sys
Mateusz Guzik
mjg at FreeBSD.org
Wed Nov 20 12:06:00 UTC 2019
Author: mjg
Date: Wed Nov 20 12:05:59 2019
New Revision: 354890
URL: https://svnweb.freebsd.org/changeset/base/354890
Log:
vfs: change si_usecount management to count used vnodes
Currently si_usecount is effectively a sum of usecounts from all associated
vnodes. This is maintained by special-casing for VCHR every time usecount is
modified. Apart from complicating the code a little bit, it has a scalability
impact since it forces a read from a cacheline shared with said count.
There are no consumers of the feature in the ports tree. In head there are only
2: revoke and devfs_close. Both can get away with a weaker requirement than the
exact usecount, namely just the count of active vnodes. Changing the meaning to
the latter means we only need to modify it on 0<->1 transitions, avoiding the
check plenty of times (and entirely in something like vrefact).
Reviewed by: kib, jeff
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22202
Modified:
head/sys/fs/devfs/devfs_vnops.c
head/sys/kern/vfs_subr.c
head/sys/kern/vfs_syscalls.c
head/sys/sys/conf.h
Modified: head/sys/fs/devfs/devfs_vnops.c
==============================================================================
--- head/sys/fs/devfs/devfs_vnops.c Wed Nov 20 11:12:19 2019 (r354889)
+++ head/sys/fs/devfs/devfs_vnops.c Wed Nov 20 12:05:59 2019 (r354890)
@@ -481,7 +481,7 @@ loop:
vp->v_rdev = dev;
KASSERT(vp->v_usecount == 1,
("%s %d (%d)\n", __func__, __LINE__, vp->v_usecount));
- dev->si_usecount += vp->v_usecount;
+ dev->si_usecount++;
/* Special casing of ttys for deadfs. Probably redundant. */
dsw = dev->si_devsw;
if (dsw != NULL && (dsw->d_flags & D_TTY) != 0)
@@ -581,7 +581,7 @@ devfs_close(struct vop_close_args *ap)
* if the reference count is 2 (this last descriptor
* plus the session), release the reference from the session.
*/
- if (td != NULL) {
+ if (vp->v_usecount == 2 && td != NULL) {
p = td->td_proc;
PROC_LOCK(p);
if (vp == p->p_session->s_ttyvp) {
@@ -591,7 +591,7 @@ devfs_close(struct vop_close_args *ap)
if (vp == p->p_session->s_ttyvp) {
SESS_LOCK(p->p_session);
VI_LOCK(vp);
- if (count_dev(dev) == 2 &&
+ if (vp->v_usecount == 2 && vcount(vp) == 1 &&
(vp->v_iflag & VI_DOOMED) == 0) {
p->p_session->s_ttyvp = NULL;
p->p_session->s_ttydp = NULL;
@@ -620,19 +620,19 @@ devfs_close(struct vop_close_args *ap)
return (ENXIO);
dflags = 0;
VI_LOCK(vp);
+ if (vp->v_usecount == 1 && vcount(vp) == 1)
+ dflags |= FLASTCLOSE;
if (vp->v_iflag & VI_DOOMED) {
/* Forced close. */
dflags |= FREVOKE | FNONBLOCK;
} else if (dsw->d_flags & D_TRACKCLOSE) {
/* Keep device updated on status. */
- } else if (count_dev(dev) > 1) {
+ } else if ((dflags & FLASTCLOSE) == 0) {
VI_UNLOCK(vp);
dev_relthread(dev, ref);
return (0);
}
- if (count_dev(dev) == 1)
- dflags |= FLASTCLOSE;
- vholdl(vp);
+ vholdnz(vp);
VI_UNLOCK(vp);
vp_locked = VOP_ISLOCKED(vp);
VOP_UNLOCK(vp, 0);
@@ -1425,7 +1425,7 @@ devfs_reclaim_vchr(struct vop_reclaim_args *ap)
dev = vp->v_rdev;
vp->v_rdev = NULL;
if (dev != NULL)
- dev->si_usecount -= vp->v_usecount;
+ dev->si_usecount -= (vp->v_usecount > 0);
dev_unlock();
VI_UNLOCK(vp);
if (dev != NULL)
Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c Wed Nov 20 11:12:19 2019 (r354889)
+++ head/sys/kern/vfs_subr.c Wed Nov 20 12:05:59 2019 (r354890)
@@ -2714,26 +2714,11 @@ _vget_prep(struct vnode *vp, bool interlock)
{
enum vgetstate vs;
- if (__predict_true(vp->v_type != VCHR)) {
- if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
- vs = VGET_USECOUNT;
- } else {
- _vhold(vp, interlock);
- vs = VGET_HOLDCNT;
- }
+ if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
+ vs = VGET_USECOUNT;
} else {
- if (!interlock)
- VI_LOCK(vp);
- if (vp->v_usecount == 0) {
- vholdl(vp);
- vs = VGET_HOLDCNT;
- } else {
- v_incr_devcount(vp);
- refcount_acquire(&vp->v_usecount);
- vs = VGET_USECOUNT;
- }
- if (!interlock)
- VI_UNLOCK(vp);
+ _vhold(vp, interlock);
+ vs = VGET_HOLDCNT;
}
return (vs);
}
@@ -2796,8 +2781,7 @@ vget_finish(struct vnode *vp, int flags, enum vgetstat
* the vnode around. Otherwise someone else lended their hold count and
* we have to drop ours.
*/
- if (vp->v_type != VCHR &&
- refcount_acquire_if_not_zero(&vp->v_usecount)) {
+ if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
#ifdef INVARIANTS
int old = atomic_fetchadd_int(&vp->v_holdcnt, -1) - 1;
VNASSERT(old > 0, vp, ("%s: wrong hold count", __func__));
@@ -2823,24 +2807,19 @@ vget_finish(struct vnode *vp, int flags, enum vgetstat
* See the previous section. By the time we get here we may find
* ourselves in the same spot.
*/
- if (vp->v_type != VCHR) {
- if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
+ if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
#ifdef INVARIANTS
- int old = atomic_fetchadd_int(&vp->v_holdcnt, -1) - 1;
- VNASSERT(old > 0, vp, ("%s: wrong hold count", __func__));
+ int old = atomic_fetchadd_int(&vp->v_holdcnt, -1) - 1;
+ VNASSERT(old > 0, vp, ("%s: wrong hold count", __func__));
#else
- refcount_release(&vp->v_holdcnt);
+ refcount_release(&vp->v_holdcnt);
#endif
- VNODE_REFCOUNT_FENCE_ACQ();
- VNASSERT((vp->v_iflag & VI_OWEINACT) == 0, vp,
- ("%s: vnode with usecount and VI_OWEINACT set",
- __func__));
- VI_UNLOCK(vp);
- return (0);
- }
- } else {
- if (vp->v_usecount > 0)
- refcount_release(&vp->v_holdcnt);
+ VNODE_REFCOUNT_FENCE_ACQ();
+ VNASSERT((vp->v_iflag & VI_OWEINACT) == 0, vp,
+ ("%s: vnode with usecount and VI_OWEINACT set",
+ __func__));
+ VI_UNLOCK(vp);
+ return (0);
}
if ((vp->v_iflag & VI_OWEINACT) == 0) {
oweinact = 0;
@@ -2868,8 +2847,7 @@ vref(struct vnode *vp)
ASSERT_VI_UNLOCKED(vp, __func__);
CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
- if (vp->v_type != VCHR &&
- refcount_acquire_if_not_zero(&vp->v_usecount)) {
+ if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
VNODE_REFCOUNT_FENCE_ACQ();
VNASSERT(vp->v_holdcnt > 0, vp,
("%s: active vnode not held", __func__));
@@ -2888,8 +2866,7 @@ vrefl(struct vnode *vp)
ASSERT_VI_LOCKED(vp, __func__);
CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
- if (vp->v_type != VCHR &&
- refcount_acquire_if_not_zero(&vp->v_usecount)) {
+ if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
VNODE_REFCOUNT_FENCE_ACQ();
VNASSERT(vp->v_holdcnt > 0, vp,
("%s: active vnode not held", __func__));
@@ -2897,8 +2874,7 @@ vrefl(struct vnode *vp)
("%s: vnode with usecount and VI_OWEINACT set", __func__));
return;
}
- if (vp->v_usecount == 0)
- vholdl(vp);
+ vholdl(vp);
if ((vp->v_iflag & VI_OWEINACT) != 0) {
vp->v_iflag &= ~VI_OWEINACT;
VNODE_REFCOUNT_FENCE_REL();
@@ -2912,12 +2888,6 @@ vrefact(struct vnode *vp)
{
CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
- if (__predict_false(vp->v_type == VCHR)) {
- VNASSERT(vp->v_holdcnt > 0 && vp->v_usecount > 0, vp,
- ("%s: wrong ref counts", __func__));
- vref(vp);
- return;
- }
#ifdef INVARIANTS
int old = atomic_fetchadd_int(&vp->v_usecount, 1);
VNASSERT(old > 0, vp, ("%s: wrong use count", __func__));
@@ -2986,31 +2956,22 @@ vputx(struct vnode *vp, int func)
* We want to hold the vnode until the inactive finishes to
* prevent vgone() races. We drop the use count here and the
* hold count below when we're done.
+ *
+ * If we release the last usecount we take ownership of the hold
+ * count which provides liveness of the vnode, in which case we
+ * have to vdrop.
*/
- if (vp->v_type != VCHR) {
- /*
- * If we release the last usecount we take ownership of the hold
- * count which provides liveness of the vnode, in which case we
- * have to vdrop.
- */
- if (!refcount_release(&vp->v_usecount))
- return;
- VI_LOCK(vp);
- /*
- * By the time we got here someone else might have transitioned
- * the count back to > 0.
- */
- if (vp->v_usecount > 0) {
- vdropl(vp);
- return;
- }
- } else {
- VI_LOCK(vp);
- v_decr_devcount(vp);
- if (!refcount_release(&vp->v_usecount)) {
- VI_UNLOCK(vp);
- return;
- }
+ if (!refcount_release(&vp->v_usecount))
+ return;
+ VI_LOCK(vp);
+ v_decr_devcount(vp);
+ /*
+ * By the time we got here someone else might have transitioned
+ * the count back to > 0.
+ */
+ if (vp->v_usecount > 0) {
+ vdropl(vp);
+ return;
}
if (vp->v_iflag & VI_DOINGINACT) {
vdropl(vp);
@@ -3737,20 +3698,6 @@ vcount(struct vnode *vp)
count = vp->v_rdev->si_usecount;
dev_unlock();
return (count);
-}
-
-/*
- * Same as above, but using the struct cdev *as argument
- */
-int
-count_dev(struct cdev *dev)
-{
- int count;
-
- dev_lock();
- count = dev->si_usecount;
- dev_unlock();
- return(count);
}
/*
Modified: head/sys/kern/vfs_syscalls.c
==============================================================================
--- head/sys/kern/vfs_syscalls.c Wed Nov 20 11:12:19 2019 (r354889)
+++ head/sys/kern/vfs_syscalls.c Wed Nov 20 12:05:59 2019 (r354890)
@@ -4148,7 +4148,7 @@ sys_revoke(struct thread *td, struct revoke_args *uap)
if (error != 0)
goto out;
}
- if (vcount(vp) > 1)
+ if (vp->v_usecount > 1 || vcount(vp) > 1)
VOP_REVOKE(vp, REVOKEALL);
out:
vput(vp);
Modified: head/sys/sys/conf.h
==============================================================================
--- head/sys/sys/conf.h Wed Nov 20 11:12:19 2019 (r354889)
+++ head/sys/sys/conf.h Wed Nov 20 12:05:59 2019 (r354890)
@@ -256,7 +256,6 @@ void make_dev_args_init_impl(struct make_dev_args *_ar
#define make_dev_args_init(a) \
make_dev_args_init_impl((a), sizeof(struct make_dev_args))
-int count_dev(struct cdev *_dev);
void delist_dev(struct cdev *_dev);
void destroy_dev(struct cdev *_dev);
int destroy_dev_sched(struct cdev *dev);
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