[PATCH] vmscan: try harder for GFP_NOFS allocators

Page reclaim bales out very early if reclaim isn't working out for !__GFP_FS
allocation attempts.

It was a fairly arbitrary thing in the first place and chances are the caller
will simply retry the allocation or will do something which is disruptive to
userspace.  So remove that code and do much more scanning.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/vmscan.c

@@ -845,14 +845,10 @@ shrink_caches(struct zone **zones, int priority, int *total_scanned,
  *
  * If the caller is !__GFP_FS then the probability of a failure is reasonably
  * high - the zone may be full of dirty or under-writeback pages, which this
- * caller can't do much about.  So for !__GFP_FS callers, we just perform a
- * small LRU walk and if that didn't work out, fail the allocation back to the
- * caller.  GFP_NOFS allocators need to know how to deal with it.  Kicking
- * bdflush, waiting and retrying will work.
- *
- * This is a fairly lame algorithm - it can result in excessive CPU burning and
- * excessive rotation of the inactive list, which is _supposed_ to be an LRU,
- * yes?
+ * caller can't do much about.  We kick pdflush and take explicit naps in the
+ * hope that some of these pages can be written.  But if the allocating task
+ * holds filesystem locks which prevent writeout this might not work, and the
+ * allocation attempt will fail.
  */
 int try_to_free_pages(struct zone **zones,
 		unsigned int gfp_mask, unsigned int order)
@@ -886,8 +882,6 @@ int try_to_free_pages(struct zone **zones,
 			ret = 1;
 			goto out;
 		}
-		if (!(gfp_mask & __GFP_FS))
-			break;		/* Let the caller handle it */
 		/*
 		 * Try to write back as many pages as we just scanned.  This
 		 * tends to cause slow streaming writers to write data to the