[PATCH 34/49] writeback: make bdi->min/max_ratio handling cgroup writeback aware

Tejun Heo
2015-04-06T20:13:55Z

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>
---
mm/page-writeback.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 46 insertions(+), 4 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ba2b83d..8755f80 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -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;
}
--
2.1.0