[PATCH][for -mm] Fix and Enhancements for memory cgroup [4/6] avoid handling !LRU page in mem_cgroup_isolate_pages

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

This patch makes mem_cgroup_isolate_pages() to be

  - ignore !PageLRU pages.
  - fixes the bug that it makes no progress if page_zone(page) != zone
    page once find. (just increment scan in this case.)

kswapd and memory migraion removes a page from list when it handles
a page for reclaiming/migration. 

__isolate_lru_page() doesn't moves page !PageLRU pages, then, it will
be safe to avoid touching the page and its page_cgroup.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

 mm/memcontrol.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -227,7 +227,7 @@ unsigned long mem_cgroup_isolate_pages(u
 	unsigned long scan;
 	LIST_HEAD(pc_list);
 	struct list_head *src;
-	struct page_cgroup *pc;
+	struct page_cgroup *pc, *tmp;
 
 	if (active)
 		src = &mem_cont->active_list;
@@ -235,11 +235,18 @@ unsigned long mem_cgroup_isolate_pages(u
 		src = &mem_cont->inactive_list;
 
 	spin_lock(&mem_cont->lru_lock);
-	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
-		pc = list_entry(src->prev, struct page_cgroup, lru);
+	scan = 0;
+	list_for_each_entry_safe_reverse(pc, tmp, src, lru) {
+		if (scan++ > nr_taken)
+			break;
 		page = pc->page;
 		VM_BUG_ON(!pc);
 
+		if (unlikely(!PageLRU(page))) {
+			scan--;
+			continue;
+		}
+
 		if (PageActive(page) && !active) {
 			__mem_cgroup_move_lists(pc, true);
 			scan--;

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