[RFC PATCH 3/4] memcontrol: apply new local_schedule_work_on() interface

[Leonardo Bras]

Make use of the new local_*lock_n*() and local_schedule_work_on() interface
to improve performance & latency on PREEMTP_RT kernels.

For functions that may be scheduled in a different cpu, replace
local_*lock*() by local_lock_n*(), and replace schedule_work_on() by
local_schedule_work_on().

This should bring no relevant performance impact on non-RT kernels:
For functions that may be scheduled in a different cpu, the local_*lock's
this_cpu_ptr() becomes a per_cpu_ptr(smp_processor_id()).

Signed-off-by: Leonardo Bras <leobras@xxxxxxxxxx>
---
 mm/memcontrol.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e8ca4bdcb03c..6d4fa48d75e3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2277,7 +2277,7 @@ static void drain_stock(struct memcg_stock_pcp *stock)
 	WRITE_ONCE(stock->cached, NULL);
 }
 
-static void drain_local_stock(struct work_struct *dummy)
+static void _drain_local_stock(int cpu)
 {
 	struct memcg_stock_pcp *stock;
 	struct obj_cgroup *old = NULL;
@@ -2288,18 +2288,23 @@ static void drain_local_stock(struct work_struct *dummy)
 	 * drain_stock races is that we always operate on local CPU stock
 	 * here with IRQ disabled
 	 */
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	local_lock_irqsave_n(&memcg_stock.stock_lock, flags, cpu);
 
-	stock = this_cpu_ptr(&memcg_stock);
+	stock = per_cpu_ptr(&memcg_stock, cpu);
 	old = drain_obj_stock(stock);
 	drain_stock(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore_n(&memcg_stock.stock_lock, flags, cpu);
 	if (old)
 		obj_cgroup_put(old);
 }
 
+static void drain_local_stock(struct work_struct *w)
+{
+	_drain_local_stock((int)w->data.counter);
+}
+
 /*
  * Cache charges(val) to local per_cpu area.
  * This will be consumed by consume_stock() function, later.
@@ -2365,9 +2370,9 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
 		if (flush &&
 		    !test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
 			if (cpu == curcpu)
-				drain_local_stock(&stock->work);
+				_drain_local_stock(cpu);
 			else if (!cpu_is_isolated(cpu))
-				schedule_work_on(cpu, &stock->work);
+				local_queue_work_on(cpu, system_wq, &stock->work);
 		}
 	}
 	migrate_enable();
-- 
2.41.0