Index: sys/kern/vfs_bio.c
===================================================================
--- sys/kern/vfs_bio.c
+++ sys/kern/vfs_bio.c
@@ -4170,6 +4170,23 @@
 }
 
 /*
+ * Return true if new buffer should be malloc'ed.
+ */
+
+static bool
+want_malloc_buf(struct buf *bp, int newbsize)
+{
+
+	if (bp->b_bufsize != 0)
+		return (false);
+	if (newbsize > PAGE_SIZE / 2)
+		return (false);
+	if (bufmallocspace >= maxbufmallocspace)
+		return (false);
+	return (true);
+}
+
+/*
  * Truncate the backing store for a non-vmio buffer.
  */
 static void
@@ -4211,8 +4228,7 @@
 	 * is probably extremely rare and not worth worrying
 	 * over.
 	 */
-	if (bp->b_bufsize == 0 && newbsize <= PAGE_SIZE/2 &&
-	    bufmallocspace < maxbufmallocspace) {
+	if (want_malloc_buf(bp, newbsize)) {
 		bp->b_data = malloc(newbsize, M_BIOBUF, M_WAITOK);
 		bp->b_flags |= B_MALLOC;
 		bufmallocadjust(bp, newbsize);
@@ -4272,7 +4288,8 @@
 
 	newbsize = roundup2(size, DEV_BSIZE);
 	if ((bp->b_flags & B_VMIO) == 0) {
-		if ((bp->b_flags & B_MALLOC) == 0)
+		if ((bp->b_flags & B_MALLOC) == 0 &&
+		    !want_malloc_buf(bp, newbsize))
 			newbsize = round_page(newbsize);
 		/*
 		 * Just get anonymous memory from the kernel.  Don't