[PATCH 4/9] writeback: track if we're sleeping on progress in balance_dirty_pages()

[Jens Axboe]

Note in the bdi_writeback structure if a task is currently being
limited in balance_dirty_pages(), waiting for writeback to
proceed.

Signed-off-by: Jens Axboe <ax...@fb.com>
---
 include/linux/backing-dev-defs.h | 2 ++
 mm/page-writeback.c              | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 1b4d69f68c33..f702309216b4 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -116,6 +116,8 @@ struct bdi_writeback {
        struct list_head work_list;
        struct delayed_work dwork;      /* work item used for writeback */
 
+       int dirty_sleeping;             /* waiting on dirty limit exceeded */
+
        struct list_head bdi_node;      /* anchored at bdi->wb_list */
 
 #ifdef CONFIG_CGROUP_WRITEBACK
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 11ff8f758631..15e696bc5d14 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1746,7 +1746,9 @@ pause:
                                          pause,
                                          start_time);
                __set_current_state(TASK_KILLABLE);
+               wb->dirty_sleeping = 1;
                io_schedule_timeout(pause);
+               wb->dirty_sleeping = 0;
 
                current->dirty_paused_when = now + pause;
                current->nr_dirtied = 0;
-- 
2.8.0.rc4.6.g7e4ba36