[PATCH] mm: account NR_WRITTEN at IO completion time

[Wu Fengguang]

NR_WRITTEN is now accounted at block IO enqueue time, which is not
very accurate as to common understanding. This moves NR_WRITTEN
accounting to the IO completion time and makes it more consistent
with BDI_WRITTEN, which is used for bandwidth estimation.

CC: Michael Rubin <mrubin@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 mm/page-writeback.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- linux-next.orig/mm/page-writeback.c	2011-04-18 17:28:44.000000000 +0800
+++ linux-next/mm/page-writeback.c	2011-04-18 17:30:33.000000000 +0800
@@ -1846,7 +1846,6 @@ EXPORT_SYMBOL(account_page_dirtied);
 void account_page_writeback(struct page *page)
 {
 	inc_zone_page_state(page, NR_WRITEBACK);
-	inc_zone_page_state(page, NR_WRITTEN);
 }
 EXPORT_SYMBOL(account_page_writeback);
 
@@ -2063,8 +2062,10 @@ int test_clear_page_writeback(struct pag
 	} else {
 		ret = TestClearPageWriteback(page);
 	}
-	if (ret)
+	if (ret) {
 		dec_zone_page_state(page, NR_WRITEBACK);
+		inc_zone_page_state(page, NR_WRITTEN);
+	}
 	return ret;
 }
 
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