[PATCH v2] mm/page_alloc: fix counting of free pages after take off from buddy

[Ding Hui <dinghui@sangfor.com.cn>]

Recently we found there is a lot MemFree left in /proc/meminfo after
do a lot of pages soft offline.

I think it's incorrect since NR_FREE_PAGES should not contain HWPoison pages.
For offline free pages, after a successful call take_page_off_buddy(), the
page is no longer belong to buddy allocator, and will not be used any more,
but we missed accounting NR_FREE_PAGES in this situation.

Do update like rmqueue() does.

Signed-off-by: Ding Hui <dinghui@sangfor.com.cn>
---
V2:
use __mod_zone_freepage_state instead of __mod_zone_page_state

 mm/page_alloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cfc72873961d..e124a615303b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8947,6 +8947,7 @@ bool take_page_off_buddy(struct page *page)
 			del_page_from_free_list(page_head, zone, page_order);
 			break_down_buddy_pages(zone, page_head, page, 0,
 						page_order, migratetype);
+			__mod_zone_freepage_state(zone, -1, migratetype);
 			ret = true;
 			break;
 		}
-- 
2.17.1