[src/ad-namecache]: src/sys/kern Turns out there's no point adjusting v_holdc...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/3c497e7985d1
branches:  ad-namecache
changeset: 1025054:3c497e7985d1
user:      ad <ad%NetBSD.org@localhost>
date:      Sun Feb 23 19:14:03 2020 +0000

description:
Turns out there's no point adjusting v_holdcnt with atomics.

diffstat:

 sys/kern/vfs_vnode.c |  38 ++++++++------------------------------
 1 files changed, 8 insertions(+), 30 deletions(-)

diffs (88 lines):

diff -r a209ad7f5051 -r 3c497e7985d1 sys/kern/vfs_vnode.c
--- a/sys/kern/vfs_vnode.c      Sun Feb 16 22:00:53 2020 +0000
+++ b/sys/kern/vfs_vnode.c      Sun Feb 23 19:14:03 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_vnode.c,v 1.105.2.7 2020/01/25 22:38:51 ad Exp $   */
+/*     $NetBSD: vfs_vnode.c,v 1.105.2.8 2020/02/23 19:14:03 ad Exp $   */
 
 /*-
  * Copyright (c) 1997-2011, 2019 The NetBSD Foundation, Inc.
@@ -142,10 +142,10 @@
  *     as vput(9), routines.  Common points holding references are e.g.
  *     file openings, current working directory, mount points, etc.  
  *
- * Note on v_usecount & v_holdcnt and their locking
+ * Note on v_usecount and its locking
  *
- *     At nearly all points it is known that the counts could be zero,
- *     the vnode_t::v_interlock will be held.  To change the counts away
+ *     At nearly all points it is known that v_usecount could be zero,
+ *     the vnode_t::v_interlock will be held.  To change the count away
  *     from zero, the interlock must be held.  To change from a non-zero
  *     value to zero, again the interlock must be held.
  *
@@ -154,7 +154,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.105.2.7 2020/01/25 22:38:51 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.105.2.8 2020/02/23 19:14:03 ad Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_pax.h"
@@ -939,7 +939,7 @@
 
        KASSERT(mutex_owned(vp->v_interlock));
 
-       if (atomic_inc_uint_nv(&vp->v_holdcnt) == 1 && vp->v_usecount == 0)
+       if (vp->v_holdcnt++ == 0 && vp->v_usecount == 0)
                lru_requeue(vp, lru_which(vp));
 }
 
@@ -949,17 +949,6 @@
 void
 vhold(vnode_t *vp)
 {
-       int hold, next;
-
-       for (hold = vp->v_holdcnt;; hold = next) {
-               if (__predict_false(hold == 0)) {
-                       break;
-               }
-               next = atomic_cas_uint(&vp->v_holdcnt, hold, hold + 1);
-               if (__predict_true(next == hold)) {
-                       return;
-               }
-       }
 
        mutex_enter(vp->v_interlock);
        vholdl(vp);
@@ -980,7 +969,8 @@
                vnpanic(vp, "%s: holdcnt vp %p", __func__, vp);
        }
 
-       if (atomic_dec_uint_nv(&vp->v_holdcnt) == 0 && vp->v_usecount == 0)
+       vp->v_holdcnt--;
+       if (vp->v_holdcnt == 0 && vp->v_usecount == 0)
                lru_requeue(vp, lru_which(vp));
 }
 
@@ -990,18 +980,6 @@
 void
 holdrele(vnode_t *vp)
 {
-       int hold, next;
-
-       for (hold = vp->v_holdcnt;; hold = next) {
-               if (__predict_false(hold == 1)) {
-                       break;
-               }
-               KASSERT(hold > 1);
-               next = atomic_cas_uint(&vp->v_holdcnt, hold, hold - 1);
-               if (__predict_true(next == hold)) {
-                       return;
-               }
-       }
 
        mutex_enter(vp->v_interlock);
        holdrelel(vp);