Move the comment about resident pages preventing vnode from leaving

active list, into the header comment for vdrop(), which is the
function that decides whether to leave the vnode on the list.  Note
that dirty page write-out in vinactive() is asynchronous.

Discussed with:	alc
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

1 files changed, 11 insertions, 5 deletions

diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index 9d0a227..5421e4d 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -2618,6 +2618,10 @@ _vhold(struct vnode *vp, bool locked)
  * Drop the hold count of the vnode.  If this is the last reference to
  * the vnode we place it on the free list unless it has been vgone'd
  * (marked VI_DOOMED) in which case we will free it.
+ *
+ * Because the vnode vm object keeps a hold reference on the vnode if
+ * there is at least one resident non-cached page, the vnode cannot
+ * leave the active list without the page cleanup done.
  */
 void
 _vdrop(struct vnode *vp, bool locked)
@@ -2744,11 +2748,13 @@ vinactive(struct vnode *vp, struct thread *td)
 	VI_UNLOCK(vp);
 	/*
 	 * Before moving off the active list, we must be sure that any
-	 * modified pages are on the vnode's dirty list since these will
-	 * no longer be checked once the vnode is on the inactive list.
-	 * Because the vnode vm object keeps a hold reference on the vnode
-	 * if there is at least one resident non-cached page, the vnode
-	 * cannot leave the active list without the page cleanup done.
+	 * modified pages are converted into the vnode's dirty
+	 * buffers, since these will no longer be checked once the
+	 * vnode is on the inactive list.
+	 *
+	 * The write-out of the dirty pages is asynchronous.  At the
+	 * point that VOP_INACTIVE() is called, there could still be
+	 * pending I/O and dirty pages in the object.
 	 */
 	obj = vp->v_object;
 	if (obj != NULL && (obj->flags & OBJ_MIGHTBEDIRTY) != 0) {