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Commit 028c2dd1 authored by Dave Chinner's avatar Dave Chinner Committed by Jens Axboe
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writeback: Add tracing to balance_dirty_pages 



Tracing high level background writeback events is good, but it doesn't
give the entire picture. Add visibility into write throttling to catch IO
dispatched by foreground throttling of processing dirtying lots of pages.

Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent 455b2864

fs/fs-writeback.c

+5 −0
Original line number Diff line number Diff line
@@ -656,10 +656,14 @@ static long wb_writeback(struct bdi_writeback *wb, 
		wbc.more_io = 0;

		wbc.nr_to_write = MAX_WRITEBACK_PAGES;

		wbc.pages_skipped = 0;



		trace_wbc_writeback_start(&wbc, wb->bdi);

		if (work->sb)

			__writeback_inodes_sb(work->sb, wb, &wbc);

		else

			writeback_inodes_wb(wb, &wbc);

		trace_wbc_writeback_written(&wbc, wb->bdi);



		work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;

		wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
@@ -687,6 +691,7 @@ static long wb_writeback(struct bdi_writeback *wb, 
		if (!list_empty(&wb->b_more_io))  {

			inode = list_entry(wb->b_more_io.prev,

						struct inode, i_list);

			trace_wbc_writeback_wait(&wbc, wb->bdi);

			inode_wait_for_writeback(inode);

		}

		spin_unlock(&inode_lock);

include/trace/events/writeback.h

+64 −0
Original line number Diff line number Diff line
@@ -85,6 +85,70 @@ DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister); 
DEFINE_WRITEBACK_EVENT(writeback_thread_start);

DEFINE_WRITEBACK_EVENT(writeback_thread_stop);



DECLARE_EVENT_CLASS(wbc_class,

	TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi),

	TP_ARGS(wbc, bdi),

	TP_STRUCT__entry(

		__array(char, name, 32)

		__field(long, nr_to_write)

		__field(long, pages_skipped)

		__field(int, sync_mode)

		__field(int, nonblocking)

		__field(int, encountered_congestion)

		__field(int, for_kupdate)

		__field(int, for_background)

		__field(int, for_reclaim)

		__field(int, range_cyclic)

		__field(int, more_io)

		__field(unsigned long, older_than_this)

		__field(long, range_start)

		__field(long, range_end)

	),



	TP_fast_assign(

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

		__entry->nr_to_write	= wbc->nr_to_write;

		__entry->pages_skipped	= wbc->pages_skipped;

		__entry->sync_mode	= wbc->sync_mode;

		__entry->for_kupdate	= wbc->for_kupdate;

		__entry->for_background	= wbc->for_background;

		__entry->for_reclaim	= wbc->for_reclaim;

		__entry->range_cyclic	= wbc->range_cyclic;

		__entry->more_io	= wbc->more_io;

		__entry->older_than_this = wbc->older_than_this ?

						*wbc->older_than_this : 0;

		__entry->range_start	= (long)wbc->range_start;

		__entry->range_end	= (long)wbc->range_end;

	),



	TP_printk("bdi %s: towrt=%ld skip=%ld mode=%d kupd=%d "

		"bgrd=%d reclm=%d cyclic=%d more=%d older=0x%lx "

		"start=0x%lx end=0x%lx",

		__entry->name,

		__entry->nr_to_write,

		__entry->pages_skipped,

		__entry->sync_mode,

		__entry->for_kupdate,

		__entry->for_background,

		__entry->for_reclaim,

		__entry->range_cyclic,

		__entry->more_io,

		__entry->older_than_this,

		__entry->range_start,

		__entry->range_end)

)



#define DEFINE_WBC_EVENT(name) \

DEFINE_EVENT(wbc_class, name, \

	TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi), \

	TP_ARGS(wbc, bdi))

DEFINE_WBC_EVENT(wbc_writeback_start);

DEFINE_WBC_EVENT(wbc_writeback_written);

DEFINE_WBC_EVENT(wbc_writeback_wait);

DEFINE_WBC_EVENT(wbc_balance_dirty_start);

DEFINE_WBC_EVENT(wbc_balance_dirty_written);

DEFINE_WBC_EVENT(wbc_balance_dirty_wait);



#endif /* _TRACE_WRITEBACK_H */



/* This part must be outside protection */

mm/page-writeback.c

+4 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ 
#include <linux/syscalls.h>

#include <linux/buffer_head.h>

#include <linux/pagevec.h>

#include <trace/events/writeback.h>



/*

 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
@@ -535,11 +536,13 @@ static void balance_dirty_pages(struct address_space *mapping, 
		 * threshold otherwise wait until the disk writes catch

		 * up.

		 */

		trace_wbc_balance_dirty_start(&wbc, bdi);

		if (bdi_nr_reclaimable > bdi_thresh) {

			writeback_inodes_wb(&bdi->wb, &wbc);

			pages_written += write_chunk - wbc.nr_to_write;

			get_dirty_limits(&background_thresh, &dirty_thresh,

				       &bdi_thresh, bdi);

			trace_wbc_balance_dirty_written(&wbc, bdi);

		}



		/*
@@ -565,6 +568,7 @@ static void balance_dirty_pages(struct address_space *mapping, 
		if (pages_written >= write_chunk)

			break;		/* We've done our duty */



		trace_wbc_balance_dirty_wait(&wbc, bdi);

		__set_current_state(TASK_INTERRUPTIBLE);

		io_schedule_timeout(pause);