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>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b55699cd9067..c735bd770d3d 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;
                 }