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, 38 insertions, 11 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index c3b92010d894..b1038bd686ac 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -118,7 +118,8 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
 int bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int);
-void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages);
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
+                        enum wb_reason reason);
 void bdi_start_background_writeback(struct backing_dev_info *bdi);
 int bdi_writeback_thread(void *data);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index ddb4652cb337..a378c295851f 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -39,6 +39,23 @@ enum writeback_sync_modes {
 };
 
 /*
+ * why some writeback work was initiated
+ */
+enum wb_reason {
+        WB_REASON_BACKGROUND,
+        WB_REASON_TRY_TO_FREE_PAGES,
+        WB_REASON_SYNC,
+        WB_REASON_PERIODIC,
+        WB_REASON_LAPTOP_TIMER,
+        WB_REASON_FREE_MORE_MEM,
+        WB_REASON_FS_FREE_SPACE,
+        WB_REASON_FORKER_THREAD,
+
+        WB_REASON_MAX,
+};
+extern const char *wb_reason_name[];
+
+/*
  * A control structure which tells the writeback code what to do.  These are
  * always on the stack, and hence need no locking.  They are always initialised
  * in a manner such that unspecified fields are set to zero.
@@ -69,14 +86,17 @@ struct writeback_control {
  */     
 struct bdi_writeback;
 int inode_wait(void *);
-void writeback_inodes_sb(struct super_block *);
-void writeback_inodes_sb_nr(struct super_block *, unsigned long nr);
-int writeback_inodes_sb_if_idle(struct super_block *);
-int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr);
+void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
+void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
+                                                        enum wb_reason reason);
+int writeback_inodes_sb_if_idle(struct super_block *, enum wb_reason reason);
+int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr,
+                                                        enum wb_reason reason);
 void sync_inodes_sb(struct super_block *);
-long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages);
+long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
+                                enum wb_reason reason);
 long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
-void wakeup_flusher_threads(long nr_pages);
+void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);
 
 /* writeback.h requires fs.h; it, too, is not included from here. */
 static inline void wait_on_inode(struct inode *inode)
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 1261db3916cc..b99caa8b780c 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -34,6 +34,7 @@ DECLARE_EVENT_CLASS(writeback_work_class,
                 __field(int, for_kupdate)
                 __field(int, range_cyclic)
                 __field(int, for_background)
+                __field(int, reason)
         ),
         TP_fast_assign(
                 strncpy(__entry->name, dev_name(bdi->dev), 32);
@@ -43,16 +44,18 @@ DECLARE_EVENT_CLASS(writeback_work_class,
                 __entry->for_kupdate = work->for_kupdate;
                 __entry->range_cyclic = work->range_cyclic;
                 __entry->for_background = work->for_background;
+                __entry->reason = work->reason;
         ),
         TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync_mode=%d "
-                  "kupdate=%d range_cyclic=%d background=%d",
+                  "kupdate=%d range_cyclic=%d background=%d reason=%s",
                   __entry->name,
                   MAJOR(__entry->sb_dev), MINOR(__entry->sb_dev),
                   __entry->nr_pages,
                   __entry->sync_mode,
                   __entry->for_kupdate,
                   __entry->range_cyclic,
-                  __entry->for_background
+                  __entry->for_background,
+                  wb_reason_name[__entry->reason]
         )
 );
 #define DEFINE_WRITEBACK_WORK_EVENT(name) \
@@ -165,6 +168,7 @@ TRACE_EVENT(writeback_queue_io,
                 __field(unsigned long,  older)
                 __field(long,           age)
                 __field(int,            moved)
+                __field(int,            reason)
         ),
         TP_fast_assign(
                 unsigned long *older_than_this = work->older_than_this;
@@ -173,12 +177,14 @@ TRACE_EVENT(writeback_queue_io,
                 __entry->age    = older_than_this ?
                                   (jiffies - *older_than_this) * 1000 / HZ : -1;
                 __entry->moved  = moved;
+                __entry->reason = work->reason;
         ),
-        TP_printk("bdi %s: older=%lu age=%ld enqueue=%d",
+        TP_printk("bdi %s: older=%lu age=%ld enqueue=%d reason=%s",
                 __entry->name,
                 __entry->older, /* older_than_this in jiffies */
                 __entry->age,   /* older_than_this in relative milliseconds */
-                __entry->moved)
+                __entry->moved,
+                wb_reason_name[__entry->reason])
 );
 
 TRACE_EVENT(global_dirty_state,