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

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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: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2015-05-22 17:13:49 -04:00 committed by Jens Axboe
parent e79729123f
commit 693108a8a6
1 changed files with 46 additions and 4 deletions
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50
mm/page-writeback.c
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@ -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;
}