writeback: account NR_WRITTEN at IO completion time

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.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Michael Rubin <mrubin@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 919b45eb57ad..d8767b381b9c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1141,7 +1141,6 @@ 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);
 
@@ -1358,8 +1357,10 @@ int test_clear_page_writeback(struct page *page)
         } else {
                 ret = TestClearPageWriteback(page);
         }
-        if (ret)
+        if (ret) {
                 dec_zone_page_state(page, NR_WRITEBACK);
+                inc_zone_page_state(page, NR_WRITTEN);
+        }
         return ret;
 }