vfs: introduce v_irflag and make v_type smaller

The current vnode layout is not smp-friendly by having frequently read data
avoidably sharing cachelines with very frequently modified fields. In
particular v_iflag inspected for VI_DOOMED can be found in the same line with
v_usecount. Instead make it available in the same cacheline as the v_op, v_data
and v_type which all get read all the time.

v_type is avoidably 4 bytes while the necessary data will easily fit in 1.
Shrinking it frees up 3 bytes, 2 of which get used here to introduce a new
flag field with a new value: VIRF_DOOMED.

Reviewed by:	kib, jeff
Differential Revision:	https://reviews.freebsd.org/D22715

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/kern/vfs_default.c b/sys/kern/vfs_default.c
index 8aee8abfbe7e..b12fe280bd09 100644
--- a/sys/kern/vfs_default.c
+++ b/sys/kern/vfs_default.c
@@ -594,7 +594,7 @@ vop_stdgetwritemount(ap)
 	 * Note that having a reference does not prevent forced unmount from
 	 * setting ->v_mount to NULL after the lock gets released. This is of
 	 * no consequence for typical consumers (most notably vn_start_write)
-	 * since in this case the vnode is VI_DOOMED. Unmount might have
+	 * since in this case the vnode is VIRF_DOOMED. Unmount might have
 	 * progressed far enough that its completion is only delayed by the
 	 * reference obtained here. The consumer only needs to concern itself
 	 * with releasing it.
@@ -1019,7 +1019,7 @@ vop_stdadvise(struct vop_advise_args *ap)
 	case POSIX_FADV_DONTNEED:
 		error = 0;
 		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
-		if (vp->v_iflag & VI_DOOMED) {
+		if (VN_IS_DOOMED(vp)) {
 			VOP_UNLOCK(vp, 0);
 			break;
 		}