[PATCH] don't make writers wait on their writeback in page reclaim

I had some code in page reclaim which is designed to catch the caller
of write(2) in page reclaim and force him to wait on writeout of his
own spindle's pages.

It works too well - there are large stalls in things like `cp
large-file foo' on small-memory machines.

So remove it, and rely on the other, more predictable throttling
schemes.

mm/vmscan.c

@@ -230,13 +230,8 @@ shrink_list(struct list_head *page_list, unsigned int gfp_mask,
 		 * writes.
 		 */
 		if (PageWriteback(page)) {
-			if (may_enter_fs) {
-				if (page->pte.direct ||
-					page->mapping->backing_dev_info ==
-						current->backing_dev_info) {
-					wait_on_page_writeback(page);
-				}
-			}
+			if (may_enter_fs && page_mapped(page))
+				wait_on_page_writeback(page);
 			goto keep_locked;
 		}