--- src/sys/i386/i386/busdma_machdep.c
+++ src/sys/i386/i386/busdma_machdep.c
@@ -97,7 +97,8 @@
 static struct bus_dmamap nobounce_dmamap;
 
 static int alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages);
-static int reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map);
+static int reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map,
+	int commit);
 static bus_addr_t add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map,
 				   vm_offset_t vaddr, bus_size_t size);
 static void free_bounce_page(bus_dma_tag_t dmat, struct bounce_page *bpage);
@@ -434,7 +435,12 @@
 		int s;
 
 		s = splhigh();
-	 	if (reserve_bounce_pages(dmat, map) != 0) {
+		if (flags & BUS_DMA_NOWAIT) {
+	 		if (reserve_bounce_pages(dmat, map, 0) != 0) {
+				splx(s);
+				return (ENOMEM);
+			}
+		} else if (reserve_bounce_pages(dmat, map, 1) != 0) {
 
 			/* Queue us for resources */
 			map->dmat = dmat;
@@ -799,11 +805,13 @@
 }
 
 static int
-reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map)
+reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map, int commit)
 {
 	int pages;
 
 	pages = MIN(free_bpages, map->pagesneeded - map->pagesreserved);
+	if (commit == 0 && map->pagesneeded > (map->pagesreserved + pages))
+		return (map->pagesneeded - (map->pagesreserved + pages));
 	free_bpages -= pages;
 	reserved_bpages += pages;
 	map->pagesreserved += pages;
@@ -857,7 +865,7 @@
 	free_bpages++;
 	active_bpages--;
 	if ((map = STAILQ_FIRST(&bounce_map_waitinglist)) != NULL) {
-		if (reserve_bounce_pages(map->dmat, map) == 0) {
+		if (reserve_bounce_pages(map->dmat, map, 1) == 0) {
 			STAILQ_REMOVE_HEAD(&bounce_map_waitinglist, links);
 			STAILQ_INSERT_TAIL(&bounce_map_callbacklist,
 					   map, links);