--- sys/kern/vfs_bio.c	(revision 253339)
+++ sys/kern/vfs_bio.c	(working copy)
@@ -1146,7 +1146,7 @@ 
 	if (bo->bo_dirty.bv_cnt > dirtybufthresh + 10) {
 		(void) VOP_FSYNC(bp->b_vp, MNT_NOWAIT, curthread);
 		altbufferflushes++;
-	} else if (bo->bo_dirty.bv_cnt > dirtybufthresh) {
+	} else if (bdflush_required(bo)) {
 		BO_LOCK(bo);
 		/*
 		 * Try to find a buffer to flush.
@@ -1438,6 +1438,24 @@ 
 }
 
 /*
+ *	Flushing is deemed necessary if at least one of the following is true:
+ *	- bo is hogging more than dirtybufthresh buffers (previous behavior)
+ *	- numdirtybuffers exceeds dirtybufthresh
+ *	- we are or act as bufdaemon (TDP_NORUNNINGBUF)
+ */
+int
+bdflush_required(struct bufobj *bo)
+{
+	struct thread *td = curthread;
+
+	KASSERT(bo != NULL, ("bdflush_required: NULL bo"));
+
+	return ((bo->bo_dirty.bv_cnt > dirtybufthresh) ||
+	        (numdirtybuffers > dirtybufthresh) ||
+	        (td && (td->td_pflags & TDP_NORUNNINGBUF)));
+}
+
+/*
  *	brelse:
  *
  *	Release a busy buffer and, if requested, free its resources.  The
--- sys/sys/buf.h	(revision 253339)
+++ sys/sys/buf.h	(working copy)
@@ -486,6 +486,7 @@ 
 void	bdata2bio(struct buf *bp, struct bio *bip);
 void	bwillwrite(void);
 int	buf_dirty_count_severe(void);
+int	bdflush_required(struct bufobj *bo);
 void	bremfree(struct buf *);
 void	bremfreef(struct buf *);	/* XXX Force bremfree, only for nfs. */
 int	bread(struct vnode *, daddr_t, int, struct ucred *, struct buf **);
--- sys/ufs/ffs/ffs_snapshot.c	(revision 253339)
+++ sys/ufs/ffs/ffs_snapshot.c	(working copy)
@@ -2161,7 +2161,7 @@ 
 	struct buf *nbp;
 	int bp_bdskip;
 
-	if (bo->bo_dirty.bv_cnt <= dirtybufthresh)
+	if (!bdflush_required(bo))
 		return;
 
 	td = curthread;