[PATCH 3/5] writeback: fix dirtied pages accounting on sub-page writes

[Wu Fengguang <fengguang.wu@intel.com>]

[-- Attachment #1: writeback-accurate-task-dirtied.patch --]
[-- Type: text/plain, Size: 1088 bytes --]

When dd in 512bytes, generic_perform_write() calls
balance_dirty_pages_ratelimited() 8 times for the same page, but
obviously the page is only dirtied once.

Fix it by accounting nr_dirtied at page dirty time.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 mm/page-writeback.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- linux-next.orig/mm/page-writeback.c	2011-11-17 20:57:13.000000000 +0800
+++ linux-next/mm/page-writeback.c	2011-11-17 20:57:15.000000000 +0800
@@ -1224,8 +1224,6 @@ void balance_dirty_pages_ratelimited_nr(
 	if (bdi->dirty_exceeded)
 		ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
 
-	current->nr_dirtied += nr_pages_dirtied;
-
 	preempt_disable();
 	/*
 	 * This prevents one CPU to accumulate too many dirtied pages without
@@ -1734,6 +1732,7 @@ void account_page_dirtied(struct page *p
 		__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
 		__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
 		task_io_account_write(PAGE_CACHE_SIZE);
+		current->nr_dirtied++;
 	}
 }
 EXPORT_SYMBOL(account_page_dirtied);