writeback: Add a 'reason' to wb_writeback_work

This creates a new 'reason' field in a wb_writeback_work
structure, which unambiguously identifies who initiates
writeback activity.  A 'wb_reason' enumeration has been
added to writeback.h, to enumerate the possible reasons.

The 'writeback_work_class' and tracepoint event class and
'writeback_queue_io' tracepoints are updated to include the
symbolic 'reason' in all trace events.

And the 'writeback_inodes_sbXXX' family of routines has had
a wb_stats parameter added to them, so callers can specify
why writeback is being started.

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

3 files changed, 6 insertions, 3 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 5dcaa3c756d..dd8916feb05 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -476,7 +476,8 @@ static int bdi_forker_thread(void *ptr)
                                  * the bdi from the thread. Hopefully 1024 is
                                  * large enough for efficient IO.
                                  */
-                                writeback_inodes_wb(&bdi->wb, 1024);
+                                writeback_inodes_wb(&bdi->wb, 1024,
+                                                    WB_REASON_FORKER_THREAD);
                         } else {
                                 /*
                                  * The spinlock makes sure we do not lose
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 45d36f7dc16..650846b6158 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1301,7 +1301,8 @@ void laptop_mode_timer_fn(unsigned long data)
          * threshold
          */
         if (bdi_has_dirty_io(&q->backing_dev_info))
-                bdi_start_writeback(&q->backing_dev_info, nr_pages);
+                bdi_start_writeback(&q->backing_dev_info, nr_pages,
+                                        WB_REASON_LAPTOP_TIMER);
 }
 
 /*
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b55699cd906..c735bd770d3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2181,7 +2181,8 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
                  */
                 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
                 if (total_scanned > writeback_threshold) {
-                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
+                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
+                                                WB_REASON_TRY_TO_FREE_PAGES);
                         sc->may_writepage = 1;
                 }