writeback: trace event balance_dirty_pages

Useful for analyzing the dynamics of the throttling algorithms and
debugging user reported problems.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

2 files changed, 95 insertions, 0 deletions

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index ffb5deb77ca9..0ce9f06f58c2 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -271,6 +271,79 @@ TRACE_EVENT(bdi_dirty_ratelimit,
         )
 );
 
+TRACE_EVENT(balance_dirty_pages,
+
+        TP_PROTO(struct backing_dev_info *bdi,
+                 unsigned long thresh,
+                 unsigned long bg_thresh,
+                 unsigned long dirty,
+                 unsigned long bdi_thresh,
+                 unsigned long bdi_dirty,
+                 unsigned long dirty_ratelimit,
+                 unsigned long task_ratelimit,
+                 unsigned long dirtied,
+                 long pause,
+                 unsigned long start_time),
+
+        TP_ARGS(bdi, thresh, bg_thresh, dirty, bdi_thresh, bdi_dirty,
+                dirty_ratelimit, task_ratelimit,
+                dirtied, pause, start_time),
+
+        TP_STRUCT__entry(
+                __array(         char,  bdi, 32)
+                __field(unsigned long,  limit)
+                __field(unsigned long,  setpoint)
+                __field(unsigned long,  dirty)
+                __field(unsigned long,  bdi_setpoint)
+                __field(unsigned long,  bdi_dirty)
+                __field(unsigned long,  dirty_ratelimit)
+                __field(unsigned long,  task_ratelimit)
+                __field(unsigned int,   dirtied)
+                __field(unsigned int,   dirtied_pause)
+                __field(unsigned long,  paused)
+                __field(         long,  pause)
+        ),
+
+        TP_fast_assign(
+                unsigned long freerun = (thresh + bg_thresh) / 2;
+                strlcpy(__entry->bdi, dev_name(bdi->dev), 32);
+
+                __entry->limit          = global_dirty_limit;
+                __entry->setpoint       = (global_dirty_limit + freerun) / 2;
+                __entry->dirty          = dirty;
+                __entry->bdi_setpoint   = __entry->setpoint *
+                                                bdi_thresh / (thresh + 1);
+                __entry->bdi_dirty      = bdi_dirty;
+                __entry->dirty_ratelimit = KBps(dirty_ratelimit);
+                __entry->task_ratelimit = KBps(task_ratelimit);
+                __entry->dirtied        = dirtied;
+                __entry->dirtied_pause  = current->nr_dirtied_pause;
+                __entry->pause          = pause * 1000 / HZ;
+                __entry->paused         = (jiffies - start_time) * 1000 / HZ;
+        ),
+
+
+        TP_printk("bdi %s: "
+                  "limit=%lu setpoint=%lu dirty=%lu "
+                  "bdi_setpoint=%lu bdi_dirty=%lu "
+                  "dirty_ratelimit=%lu task_ratelimit=%lu "
+                  "dirtied=%u dirtied_pause=%u "
+                  "paused=%lu pause=%ld",
+                  __entry->bdi,
+                  __entry->limit,
+                  __entry->setpoint,
+                  __entry->dirty,
+                  __entry->bdi_setpoint,
+                  __entry->bdi_dirty,
+                  __entry->dirty_ratelimit,
+                  __entry->task_ratelimit,
+                  __entry->dirtied,
+                  __entry->dirtied_pause,
+                  __entry->paused,      /* ms */
+                  __entry->pause        /* ms */
+          )
+);
+
 DECLARE_EVENT_CLASS(writeback_congest_waited_template,
 
         TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed),
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e3c2d8bf87bb..45d36f7dc169 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1103,12 +1103,34 @@ static void balance_dirty_pages(struct address_space *mapping,
                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
                 pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
                 if (unlikely(pause <= 0)) {
+                        trace_balance_dirty_pages(bdi,
+                                                  dirty_thresh,
+                                                  background_thresh,
+                                                  nr_dirty,
+                                                  bdi_thresh,
+                                                  bdi_dirty,
+                                                  dirty_ratelimit,
+                                                  task_ratelimit,
+                                                  pages_dirtied,
+                                                  pause,
+                                                  start_time);
                         pause = 1; /* avoid resetting nr_dirtied_pause below */
                         break;
                 }
                 pause = min(pause, max_pause);
 
 pause:
+                trace_balance_dirty_pages(bdi,
+                                          dirty_thresh,
+                                          background_thresh,
+                                          nr_dirty,
+                                          bdi_thresh,
+                                          bdi_dirty,
+                                          dirty_ratelimit,
+                                          task_ratelimit,
+                                          pages_dirtied,
+                                          pause,
+                                          start_time);
                 __set_current_state(TASK_UNINTERRUPTIBLE);
                 io_schedule_timeout(pause);