writeback: make laptop_mode_timer_fn() handle multiple bdi_writeback's

For cgroup writeback support, all bdi-wide operations should be
distributed to all its wb's (bdi_writeback's).

This patch updates laptop_mode_timer_fn() so that it invokes
wb_start_writeback() on all wb's rather than just the root one.  As
the intent is writing out all dirty data, there's no reason to split
the number of pages to write.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6301af2..682e3a6 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1723,14 +1723,20 @@ void laptop_mode_timer_fn(unsigned long data)
        struct request_queue *q = (struct request_queue *)data;
        int nr_pages = global_page_state(NR_FILE_DIRTY) +
                global_page_state(NR_UNSTABLE_NFS);
+       struct bdi_writeback *wb;
+       struct wb_iter iter;
 
        /*
         * We want to write everything out, not just down to the dirty
         * threshold
         */
-       if (bdi_has_dirty_io(&q->backing_dev_info))
-               wb_start_writeback(&q->backing_dev_info.wb, nr_pages, true,
-                                  WB_REASON_LAPTOP_TIMER);
+       if (!bdi_has_dirty_io(&q->backing_dev_info))
+               return;
+
+       bdi_for_each_wb(wb, &q->backing_dev_info, &iter, 0)
+               if (wb_has_dirty_io(wb))
+                       wb_start_writeback(wb, nr_pages, true,
+                                          WB_REASON_LAPTOP_TIMER);
 }
 
 /*