[patch] memory reclaim more efficiently

[Takenori Nagano <t-nagano@ah.jp.nec.com>]

Hi,

Efficiency of memory reclaim is recently one of the hot topics. (LRU splitting,
pageout throttling, etc...) I would like to contribute it and I made this patch.

In shrink_zone(), system can not return to user mode before it finishes to
search LRU list. IMHO, it is very wasteful, since the user processes stay
unnecessarily long time in shrink_zone() loop and application response time
becomes relatively bad. This patch changes shrink_zone() that it finishes memory
reclaim when it reclaims enough memory.

the conditions to end searching:

1. order of request page is 0
2. process is not kswapd.
3. satisfy the condition to return try_to_free_pages()
   # nr_reclaim > SWAP_CLUSTER_MAX


Signed-off-by: Takenori Nagano <t-nagano@ah.jp.nec.com>
Signed-off-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>

---
diff -uprN linux-2.6.26-rc6.orig/mm/vmscan.c linux-2.6.26-rc6/mm/vmscan.c
--- linux-2.6.26-rc6.orig/mm/vmscan.c	2008-06-13 06:22:24.000000000 +0900
+++ linux-2.6.26-rc6/mm/vmscan.c	2008-06-20 15:05:03.492700863 +0900
@@ -1224,6 +1224,9 @@ static unsigned long shrink_zone(int pri
 			nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
 								sc);
 		}
+		if (nr_reclaimed > sc->swap_cluster_max && !sc->order
+						&& !current_is_kswapd())
+			break;
 	}
 
 	throttle_vm_writeout(sc->gfp_mask);