[PATCH 1/1] MM: make vmpressure_win dynamic

[Fabian Frederick <fabf@skynet.be>]

Initialize vmpressure_win in vmstat using
calculate_normal_threshold() based on each zone/cpu * SWAP_CLUSTER_SIZE

Value refreshed through cpu notifier

Cc: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
---
 mm/vmpressure.c | 16 +---------------
 mm/vmstat.c     | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index d4042e7..909169d 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -24,21 +24,7 @@
 #include <linux/printk.h>
 #include <linux/vmpressure.h>
 
-/*
- * The window size (vmpressure_win) is the number of scanned pages before
- * we try to analyze scanned/reclaimed ratio. So the window is used as a
- * rate-limit tunable for the "low" level notification, and also for
- * averaging the ratio for medium/critical levels. Using small window
- * sizes can cause lot of false positives, but too big window size will
- * delay the notifications.
- *
- * As the vmscan reclaimer logic works with chunks which are multiple of
- * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
- *
- * TODO: Make the window size depend on machine size, as we do for vmstat
- * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
- */
-static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
+extern unsigned long vmpressure_win;
 
 /*
  * These thresholds are used when we account memory pressure through
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 302dd07..b8f8ff2 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -23,6 +23,23 @@
 
 #include "internal.h"
 
+/*
+ * The window size (vmpressure_win) is the number of scanned pages before
+ * we try to analyze scanned/reclaimed ratio. So the window is used as a
+ * rate-limit tunable for the "low" level notification, and also for
+ * averaging the ratio for medium/critical levels. Using small window
+ * sizes can cause lot of false positives, but too big window size will
+ * delay the notifications.
+ *
+ * As the vmscan reclaimer logic works with chunks which are multiple of
+ * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
+ *
+ */
+#ifdef CONFIG_MEMCG
+static DEFINE_SPINLOCK(vmpressure_win_lock);
+unsigned long vmpressure_win __read_mostly = SWAP_CLUSTER_MAX * 16;
+#endif
+
 #ifdef CONFIG_VM_EVENT_COUNTERS
 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
 EXPORT_PER_CPU_SYMBOL(vm_event_states);
@@ -163,11 +180,13 @@ void refresh_zone_stat_thresholds(void)
 	struct zone *zone;
 	int cpu;
 	int threshold;
+	unsigned long new_vmpressure_win = 0;
 
 	for_each_populated_zone(zone) {
 		unsigned long max_drift, tolerate_drift;
 
 		threshold = calculate_normal_threshold(zone);
+		new_vmpressure_win += threshold;
 
 		for_each_online_cpu(cpu)
 			per_cpu_ptr(zone->pageset, cpu)->stat_threshold
@@ -184,6 +203,11 @@ void refresh_zone_stat_thresholds(void)
 			zone->percpu_drift_mark = high_wmark_pages(zone) +
 					max_drift;
 	}
+#ifdef CONFIG_MEMCG
+	spin_lock(&vmpressure_win_lock);
+	vmpressure_win = new_vmpressure_win * SWAP_CLUSTER_MAX;
+	spin_unlock(&vmpressure_win_lock);
+#endif
 }
 
 void set_pgdat_percpu_threshold(pg_data_t *pgdat,
-- 
1.8.4.5