mm: vmscan: count only dirty pages as congested

shrink_page_list() counts all pages with a mapping, including clean pages,
toward nr_congested if they're on a write-congested BDI.
shrink_inactive_list() then sets ZONE_CONGESTED if nr_dirty ==
nr_congested.  Fix this apples-to-oranges comparison by only counting
pages for nr_congested if they count for nr_dirty.

Signed-off-by: Jamie Liu <jamieliu@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 59605b7c9970..53157e157061 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -874,7 +874,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                  * end of the LRU a second time.
                  */
                 mapping = page_mapping(page);
-                if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
+                if (((dirty || writeback) && mapping &&
+                     bdi_write_congested(mapping->backing_dev_info)) ||
                     (writeback && PageReclaim(page)))
                         nr_congested++;