Commit 693108a8 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

writeback: make bdi->min/max_ratio handling cgroup writeback aware 



bdi->min/max_ratio are user-configurable per-bdi knobs which regulate
dirty limit of each bdi.  For cgroup writeback, they need to be
further distributed across wb's (bdi_writeback's) belonging to the
configured bdi.

This patch introduces wb_min_max_ratio() which distributes
bdi->min/max_ratio according to a wb's proportion in the total active
bandwidth of its bdi.

v2: Update wb_min_max_ratio() to fix a bug where both min and max were
    assigned the min value and avoid calculations when possible.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent e7972912

mm/page-writeback.c

+46 −4
Original line number Diff line number Diff line
@@ -155,6 +155,46 @@ static unsigned long writeout_period_time = 0; 
 */

#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)



#ifdef CONFIG_CGROUP_WRITEBACK



static void wb_min_max_ratio(struct bdi_writeback *wb,

			     unsigned long *minp, unsigned long *maxp)

{

	unsigned long this_bw = wb->avg_write_bandwidth;

	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);

	unsigned long long min = wb->bdi->min_ratio;

	unsigned long long max = wb->bdi->max_ratio;



	/*

	 * @wb may already be clean by the time control reaches here and

	 * the total may not include its bw.

	 */

	if (this_bw < tot_bw) {

		if (min) {

			min *= this_bw;

			do_div(min, tot_bw);

		}

		if (max < 100) {

			max *= this_bw;

			do_div(max, tot_bw);

		}

	}



	*minp = min;

	*maxp = max;

}



#else	/* CONFIG_CGROUP_WRITEBACK */



static void wb_min_max_ratio(struct bdi_writeback *wb,

			     unsigned long *minp, unsigned long *maxp)

{

	*minp = wb->bdi->min_ratio;

	*maxp = wb->bdi->max_ratio;

}



#endif	/* CONFIG_CGROUP_WRITEBACK */



/*

 * In a memory zone, there is a certain amount of pages we consider

 * available for the page cache, which is essentially the number of
@@ -539,9 +579,9 @@ static unsigned long hard_dirty_limit(unsigned long thresh) 
 */

unsigned long wb_dirty_limit(struct bdi_writeback *wb, unsigned long dirty)

{

	struct backing_dev_info *bdi = wb->bdi;

	u64 wb_dirty;

	long numerator, denominator;

	unsigned long wb_min_ratio, wb_max_ratio;



	/*

	 * Calculate this BDI's share of the dirty ratio.
@@ -552,9 +592,11 @@ unsigned long wb_dirty_limit(struct bdi_writeback *wb, unsigned long dirty) 
	wb_dirty *= numerator;

	do_div(wb_dirty, denominator);



	wb_dirty += (dirty * bdi->min_ratio) / 100;

	if (wb_dirty > (dirty * bdi->max_ratio) / 100)

		wb_dirty = dirty * bdi->max_ratio / 100;

	wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);



	wb_dirty += (dirty * wb_min_ratio) / 100;

	if (wb_dirty > (dirty * wb_max_ratio) / 100)

		wb_dirty = dirty * wb_max_ratio / 100;



	return wb_dirty;

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE