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Commit daddfa3c authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
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writeback: add dirty_throttle_control->pos_ratio 



wb_position_ratio() is used to calculate pos_ratio, which is used for
two purposes.  wb_update_dirty_ratelimit() uses it to adjust
wb->[balanced_]dirty_ratelimit gradually and balance_dirty_pages() to
immediately adjust dirty_ratelimit right before applying it to
determine pause duration.

While wb_update_dirty_ratelimit() is separately rate limited from
balance_dirty_pages(), on the run where the ratelimit is updated, we
end up calculating pos_ratio twice with the same parameters.

This patch adds dirty_throttle_control->pos_ratio.
balance_dirty_pages() calculates it once per run and
wb_update_dirty_ratelimit() uses the value stored in
dirty_throttle_control.

This removes the duplicate calculation and also will help implementing
memcg wb_domain.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent b1cbc6d4

mm/page-writeback.c

+21 −15
Original line number Diff line number Diff line
@@ -135,6 +135,8 @@ struct dirty_throttle_control { 
	unsigned long		wb_dirty;	/* per-wb counterparts */

	unsigned long		wb_thresh;

	unsigned long		wb_bg_thresh;



	unsigned long		pos_ratio;

};



#define GDTC_INIT(__wb)		.wb = (__wb)
@@ -717,7 +719,7 @@ static long long pos_ratio_polynom(unsigned long setpoint, 
 *   card's wb_dirty may rush to many times higher than wb_setpoint.

 * - the wb dirty thresh drops quickly due to change of JBOD workload

 */

static unsigned long wb_position_ratio(struct dirty_throttle_control *dtc)

static void wb_position_ratio(struct dirty_throttle_control *dtc)

{

	struct bdi_writeback *wb = dtc->wb;

	unsigned long write_bw = wb->avg_write_bandwidth;
@@ -731,8 +733,10 @@ static unsigned long wb_position_ratio(struct dirty_throttle_control *dtc) 
	long long pos_ratio;		/* for scaling up/down the rate limit */

	long x;



	dtc->pos_ratio = 0;



	if (unlikely(dtc->dirty >= limit))

		return 0;

		return;



	/*

	 * global setpoint
@@ -770,18 +774,20 @@ static unsigned long wb_position_ratio(struct dirty_throttle_control *dtc) 
	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {

		long long wb_pos_ratio;



		if (dtc->wb_dirty < 8)

			return min_t(long long, pos_ratio * 2,

		if (dtc->wb_dirty < 8) {

			dtc->pos_ratio = min_t(long long, pos_ratio * 2,

					   2 << RATELIMIT_CALC_SHIFT);

			return;

		}



		if (dtc->wb_dirty >= wb_thresh)

			return 0;

			return;



		wb_setpoint = dirty_freerun_ceiling(wb_thresh,

						    dtc->wb_bg_thresh);



		if (wb_setpoint == 0 || wb_setpoint == wb_thresh)

			return 0;

			return;



		wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,

						 wb_thresh);
@@ -807,7 +813,8 @@ static unsigned long wb_position_ratio(struct dirty_throttle_control *dtc) 
		 * is 2. We might want to tweak this if we observe the control

		 * system is too slow to adapt.

		 */

		return min(pos_ratio, wb_pos_ratio);

		dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);

		return;

	}



	/*
@@ -888,7 +895,7 @@ static unsigned long wb_position_ratio(struct dirty_throttle_control *dtc) 
			pos_ratio *= 8;

	}



	return pos_ratio;

	dtc->pos_ratio = pos_ratio;

}



static void wb_update_write_bandwidth(struct bdi_writeback *wb,
@@ -1009,7 +1016,6 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, 
	unsigned long dirty_rate;

	unsigned long task_ratelimit;

	unsigned long balanced_dirty_ratelimit;

	unsigned long pos_ratio;

	unsigned long step;

	unsigned long x;
@@ -1019,12 +1025,11 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, 
	 */

	dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;



	pos_ratio = wb_position_ratio(dtc);

	/*

	 * task_ratelimit reflects each dd's dirty rate for the past 200ms.

	 */

	task_ratelimit = (u64)dirty_ratelimit *

					pos_ratio >> RATELIMIT_CALC_SHIFT;

					dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;

	task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */



	/*
@@ -1375,7 +1380,6 @@ static void balance_dirty_pages(struct address_space *mapping, 
	bool dirty_exceeded = false;

	unsigned long task_ratelimit;

	unsigned long dirty_ratelimit;

	unsigned long pos_ratio;

	struct backing_dev_info *bdi = wb->bdi;

	bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;

	unsigned long start_time = jiffies;
@@ -1433,6 +1437,9 @@ static void balance_dirty_pages(struct address_space *mapping, 


		dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&

			((gdtc->dirty > gdtc->thresh) || strictlimit);



		wb_position_ratio(gdtc);



		if (dirty_exceeded && !wb->dirty_exceeded)

			wb->dirty_exceeded = 1;
@@ -1444,8 +1451,7 @@ static void balance_dirty_pages(struct address_space *mapping, 
		}



		dirty_ratelimit = wb->dirty_ratelimit;

		pos_ratio = wb_position_ratio(gdtc);

		task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>

		task_ratelimit = ((u64)dirty_ratelimit * gdtc->pos_ratio) >>

							RATELIMIT_CALC_SHIFT;

		max_pause = wb_max_pause(wb, gdtc->wb_dirty);

		min_pause = wb_min_pause(wb, max_pause,