Index: head/sys/vm/swap_pager.c
===================================================================
--- head/sys/vm/swap_pager.c
+++ head/sys/vm/swap_pager.c
@@ -1453,18 +1453,6 @@
 		/* Maximum I/O size is limited by maximum swap block size. */
 		n = min(count - i, nsw_cluster_max);
 
-		/* Get a block of swap of size up to size n. */
-		blk = swp_pager_getswapspace(&n, 4);
-		if (blk == SWAPBLK_NONE) {
-			for (j = 0; j < n; ++j)
-				rtvals[i + j] = VM_PAGER_FAIL;
-			continue;
-		}
-
-		/*
-		 * All I/O parameters have been satisfied.  Build the I/O
-		 * request and assign the swap space.
-		 */
 		if (async) {
 			mtx_lock(&swbuf_mtx);
 			while (nsw_wcount_async == 0)
@@ -1473,19 +1461,20 @@
 			nsw_wcount_async--;
 			mtx_unlock(&swbuf_mtx);
 		}
-		bp = uma_zalloc(swwbuf_zone, M_WAITOK);
-		if (async)
-			bp->b_flags = B_ASYNC;
-		bp->b_flags |= B_PAGING;
-		bp->b_iocmd = BIO_WRITE;
 
-		bp->b_rcred = crhold(thread0.td_ucred);
-		bp->b_wcred = crhold(thread0.td_ucred);
-		bp->b_bcount = PAGE_SIZE * n;
-		bp->b_bufsize = PAGE_SIZE * n;
-		bp->b_blkno = blk;
-
+		/* Get a block of swap of size up to size n. */
 		VM_OBJECT_WLOCK(object);
+		blk = swp_pager_getswapspace(&n, 4);
+		if (blk == SWAPBLK_NONE) {
+			VM_OBJECT_WUNLOCK(object);
+			mtx_lock(&swbuf_mtx);
+			if (++nsw_wcount_async == 1)
+				wakeup(&nsw_wcount_async);
+			mtx_unlock(&swbuf_mtx);
+			for (j = 0; j < n; ++j)
+				rtvals[i + j] = VM_PAGER_FAIL;
+			continue;
+		}
 		for (j = 0; j < n; ++j) {
 			mreq = ma[i + j];
 			vm_page_aflag_clear(mreq, PGA_SWAP_FREE);
@@ -1496,10 +1485,24 @@
 				    addr);
 			MPASS(mreq->dirty == VM_PAGE_BITS_ALL);
 			mreq->oflags |= VPO_SWAPINPROG;
-			bp->b_pages[j] = mreq;
 		}
 		VM_OBJECT_WUNLOCK(object);
+
+		bp = uma_zalloc(swwbuf_zone, M_WAITOK);
+		if (async)
+			bp->b_flags = B_ASYNC;
+		bp->b_flags |= B_PAGING;
+		bp->b_iocmd = BIO_WRITE;
+
+		bp->b_rcred = crhold(thread0.td_ucred);
+		bp->b_wcred = crhold(thread0.td_ucred);
+		bp->b_bcount = PAGE_SIZE * n;
+		bp->b_bufsize = PAGE_SIZE * n;
+		bp->b_blkno = blk;
+		for (j = 0; j < n; j++)
+			bp->b_pages[j] = ma[i + j];
 		bp->b_npages = n;
+
 		/*
 		 * Must set dirty range for NFS to work.
 		 */
@@ -2059,7 +2062,7 @@
 	 * Free the swblk if we end up with the empty page run.
 	 */
 	if (swapblk == SWAPBLK_NONE)
-	    swp_pager_free_empty_swblk(object, sb);
+		swp_pager_free_empty_swblk(object, sb);
 	return (prev_swapblk);
 }