stats_flush_threshold is a misnomer. It is not actually a threshold, but
rather a number that represents the amount of updates that we have. It
is counted in multiples of MEMCG_CHARGE_BATCH. When this value reaches
num_online_cpus(), we flush the stats.
Hence, num_online_cpus() is the actual threshold, and
stats_flush_threshold is actually an order of the stats updates
magnitude. Rename stats_flush_threshold to stats_updates_order, and
define a STATS_FLUSH_THRESHOLD constant that resolves to
num_online_cpus().
No functional change intended.
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
mm/memcontrol.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 35a9c013d755..d729870505f1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -589,10 +589,12 @@ static void flush_memcg_stats_dwork(struct work_struct *w);
static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork);
static DEFINE_PER_CPU(unsigned int, stats_updates);
static atomic_t stats_flush_ongoing = ATOMIC_INIT(0);
-static atomic_t stats_flush_threshold = ATOMIC_INIT(0);
+/* stats_updates_order is in multiples of MEMCG_CHARGE_BATCH */
+static atomic_t stats_updates_order = ATOMIC_INIT(0);
static u64 flush_last_time;
#define FLUSH_TIME (2UL*HZ)
+#define STATS_FLUSH_THRESHOLD num_online_cpus()
/*
* Accessors to ensure that preemption is disabled on PREEMPT_RT because it can
@@ -628,13 +630,11 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
x = __this_cpu_add_return(stats_updates, abs(val));
if (x > MEMCG_CHARGE_BATCH) {
/*
- * If stats_flush_threshold exceeds the threshold
- * (>num_online_cpus()), cgroup stats update will be triggered
- * in __mem_cgroup_flush_stats(). Increasing this var further
- * is redundant and simply adds overhead in atomic update.
+ * Incrementing stats_updates_order beyond the threshold is
+ * redundant. Avoid the overhead of the atomic update.
*/
- if (atomic_read(&stats_flush_threshold) <= num_online_cpus())
- atomic_add(x / MEMCG_CHARGE_BATCH, &stats_flush_threshold);
+ if (atomic_read(&stats_updates_order) <= STATS_FLUSH_THRESHOLD)
+ atomic_add(x / MEMCG_CHARGE_BATCH, &stats_updates_order);
__this_cpu_write(stats_updates, 0);
}
}
@@ -654,13 +654,13 @@ static void do_flush_stats(void)
cgroup_rstat_flush(root_mem_cgroup->css.cgroup);
- atomic_set(&stats_flush_threshold, 0);
+ atomic_set(&stats_updates_order, 0);
atomic_set(&stats_flush_ongoing, 0);
}
void mem_cgroup_flush_stats(void)
{
- if (atomic_read(&stats_flush_threshold) > num_online_cpus())
+ if (atomic_read(&stats_updates_order) > STATS_FLUSH_THRESHOLD)
do_flush_stats();
}
@@ -674,8 +674,8 @@ void mem_cgroup_flush_stats_ratelimited(void)
static void flush_memcg_stats_dwork(struct work_struct *w)
{
/*
- * Always flush here so that flushing in latency-sensitive paths is
- * as cheap as possible.
+ * Deliberately ignore stats_updates_order here so that flushing in
+ * latency-sensitive paths is as cheap as possible.
*/
do_flush_stats();
queue_delayed_work(system_unbound_wq, &stats_flush_dwork, FLUSH_TIME);
--
2.42.0.283.g2d96d420d3-goog
