Commit 455b2864 authored by Dave Chinner's avatar Dave Chinner Committed by Jens Axboe
Browse files

writeback: Initial tracing support 



Trace queue/sched/exec parts of the writeback loop. This provides
insight into when and why flusher threads are scheduled to run. e.g
a sync invocation leaves traces like:

     sync-[...]: writeback_queue: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0
flush-8:0-[...]: writeback_exec: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0

This also lays the foundation for adding more writeback tracing to
provide deeper insight into the whole writeback path.

The original tracing code is from Jens Axboe, though this version is
a rewrite as a result of the code being traced changing
significantly.

Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent a89f5c89

fs/fs-writeback.c

+30 −8
Original line number Diff line number Diff line
@@ -26,15 +26,9 @@ 
#include <linux/blkdev.h>

#include <linux/backing-dev.h>

#include <linux/buffer_head.h>

#include <linux/tracepoint.h>

#include "internal.h"



#define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)



/*

 * We don't actually have pdflush, but this one is exported though /proc...

 */

int nr_pdflush_threads;



/*

 * Passed into wb_writeback(), essentially a subset of writeback_control

 */
@@ -50,6 +44,21 @@ struct wb_writeback_work { 
	struct completion *done;	/* set if the caller waits */

};



/*

 * Include the creation of the trace points after defining the

 * wb_writeback_work structure so that the definition remains local to this

 * file.

 */

#define CREATE_TRACE_POINTS

#include <trace/events/writeback.h>



#define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)



/*

 * We don't actually have pdflush, but this one is exported though /proc...

 */

int nr_pdflush_threads;



/**

 * writeback_in_progress - determine whether there is writeback in progress

 * @bdi: the device's backing_dev_info structure.
@@ -65,6 +74,8 @@ int writeback_in_progress(struct backing_dev_info *bdi) 
static void bdi_queue_work(struct backing_dev_info *bdi,

		struct wb_writeback_work *work)

{

	trace_writeback_queue(bdi, work);



	spin_lock(&bdi->wb_lock);

	list_add_tail(&work->list, &bdi->work_list);

	spin_unlock(&bdi->wb_lock);
@@ -74,6 +85,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi, 
	 * it gets created and wakes up, we'll run this work.

	 */

	if (unlikely(!bdi->wb.task)) {

		trace_writeback_nothread(bdi, work);

		wake_up_process(default_backing_dev_info.wb.task);

	} else {

		struct bdi_writeback *wb = &bdi->wb;
@@ -95,8 +107,10 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages, 
	 */

	work = kzalloc(sizeof(*work), GFP_ATOMIC);

	if (!work) {

		if (bdi->wb.task)

		if (bdi->wb.task) {

			trace_writeback_nowork(bdi);

			wake_up_process(bdi->wb.task);

		}

		return;

	}
@@ -751,6 +765,8 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait) 
		if (force_wait)

			work->sync_mode = WB_SYNC_ALL;



		trace_writeback_exec(bdi, work);



		wrote += wb_writeback(wb, work);



		/*
@@ -805,9 +821,13 @@ int bdi_writeback_thread(void *data) 
	smp_mb__after_clear_bit();

	wake_up_bit(&bdi->state, BDI_pending);



	trace_writeback_thread_start(bdi);



	while (!kthread_should_stop()) {

		pages_written = wb_do_writeback(wb, 0);



		trace_writeback_pages_written(pages_written);



		if (pages_written)

			last_active = jiffies;

		else if (wait_jiffies != -1UL) {
@@ -845,6 +865,8 @@ int bdi_writeback_thread(void *data) 
	 */

	if (!list_empty(&bdi->work_list))

		wb_do_writeback(wb, 1);



	trace_writeback_thread_stop(bdi);

	return 0;

}

include/trace/events/writeback.h

0 → 100644
+91 −0
Original line number Diff line number Diff line 
#undef TRACE_SYSTEM

#define TRACE_SYSTEM writeback



#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)

#define _TRACE_WRITEBACK_H



#include <linux/backing-dev.h>

#include <linux/writeback.h>



struct wb_writeback_work;



DECLARE_EVENT_CLASS(writeback_work_class,

	TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_work *work),

	TP_ARGS(bdi, work),

	TP_STRUCT__entry(

		__array(char, name, 32)

		__field(long, nr_pages)

		__field(dev_t, sb_dev)

		__field(int, sync_mode)

		__field(int, for_kupdate)

		__field(int, range_cyclic)

		__field(int, for_background)

	),

	TP_fast_assign(

		strncpy(__entry->name, dev_name(bdi->dev), 32);

		__entry->nr_pages = work->nr_pages;

		__entry->sb_dev = work->sb ? work->sb->s_dev : 0;

		__entry->sync_mode = work->sync_mode;

		__entry->for_kupdate = work->for_kupdate;

		__entry->range_cyclic = work->range_cyclic;

		__entry->for_background	= work->for_background;

	),

	TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync_mode=%d "

		  "kupdate=%d range_cyclic=%d background=%d",

		  __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

	)

);

#define DEFINE_WRITEBACK_WORK_EVENT(name) \

DEFINE_EVENT(writeback_work_class, name, \

	TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_work *work), \

	TP_ARGS(bdi, work))

DEFINE_WRITEBACK_WORK_EVENT(writeback_nothread);

DEFINE_WRITEBACK_WORK_EVENT(writeback_queue);

DEFINE_WRITEBACK_WORK_EVENT(writeback_exec);



TRACE_EVENT(writeback_pages_written,

	TP_PROTO(long pages_written),

	TP_ARGS(pages_written),

	TP_STRUCT__entry(

		__field(long,		pages)

	),

	TP_fast_assign(

		__entry->pages		= pages_written;

	),

	TP_printk("%ld", __entry->pages)

);



DECLARE_EVENT_CLASS(writeback_class,

	TP_PROTO(struct backing_dev_info *bdi),

	TP_ARGS(bdi),

	TP_STRUCT__entry(

		__array(char, name, 32)

	),

	TP_fast_assign(

		strncpy(__entry->name, dev_name(bdi->dev), 32);

	),

	TP_printk("bdi %s",

		  __entry->name

	)

);

#define DEFINE_WRITEBACK_EVENT(name) \

DEFINE_EVENT(writeback_class, name, \

	TP_PROTO(struct backing_dev_info *bdi), \

	TP_ARGS(bdi))



DEFINE_WRITEBACK_EVENT(writeback_nowork);

DEFINE_WRITEBACK_EVENT(writeback_bdi_register);

DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);

DEFINE_WRITEBACK_EVENT(writeback_thread_start);

DEFINE_WRITEBACK_EVENT(writeback_thread_stop);



#endif /* _TRACE_WRITEBACK_H */



/* This part must be outside protection */

#include <trace/define_trace.h>

mm/backing-dev.c

+3 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/module.h>

#include <linux/writeback.h>

#include <linux/device.h>

#include <trace/events/writeback.h>



static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
@@ -518,6 +519,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent, 


	bdi_debug_register(bdi, dev_name(dev));

	set_bit(BDI_registered, &bdi->state);

	trace_writeback_bdi_register(bdi);

exit:

	return ret;

}
@@ -578,6 +580,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi) 
void bdi_unregister(struct backing_dev_info *bdi)

{

	if (bdi->dev) {

		trace_writeback_bdi_unregister(bdi);

		bdi_prune_sb(bdi);



		if (!bdi_cap_flush_forker(bdi))

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