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>

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index ffb5deb..0ce9f06 100644 (file)
--- 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 e3c2d8b..45d36f7 100644 (file)
--- 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);