[RFC 2/5] mm, page_alloc: calculate pageset high and batch once per zone

[Vlastimil Babka]

We currently call pageset_set_high_and_batch() for each possible cpu,
which repeats the same calculations of high and batch values.

Instead call it once per zone, and it applies the calculated values
to all per-cpu pagesets of the zone.

This also allows removing zone_pageset_init() and __zone_pcp_update() wrappers.

No functional change.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/page_alloc.c | 40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0b516208afda..f669a251f654 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6236,12 +6236,13 @@ static void setup_pageset(struct per_cpu_pageset *p)
 	pageset_update(&p->pcp, 0, 1);
 }
 
-static void pageset_set_high_and_batch(struct zone *zone,
-				       struct per_cpu_pageset *p)
+static void zone_set_pageset_high_and_batch(struct zone *zone)
 {
 	unsigned long new_high;
 	unsigned long new_batch;
 	int fraction = READ_ONCE(percpu_pagelist_fraction);
+	int cpu;
+	struct per_cpu_pageset *p;
 
 	if (fraction) {
 		new_high = zone_managed_pages(zone) / fraction;
@@ -6253,23 +6254,25 @@ static void pageset_set_high_and_batch(struct zone *zone,
 		new_high = 6 * new_batch;
 		new_batch = max(1UL, 1 * new_batch);
 	}
-	pageset_update(&p->pcp, new_high, new_batch);
-}
-
-static void __meminit zone_pageset_init(struct zone *zone, int cpu)
-{
-	struct per_cpu_pageset *pcp = per_cpu_ptr(zone->pageset, cpu);
 
-	pageset_init(pcp);
-	pageset_set_high_and_batch(zone, pcp);
+	for_each_possible_cpu(cpu) {
+		p = per_cpu_ptr(zone->pageset, cpu);
+		pageset_update(&p->pcp, new_high, new_batch);
+	}
 }
 
 void __meminit setup_zone_pageset(struct zone *zone)
 {
 	int cpu;
+	struct per_cpu_pageset *p;
+
 	zone->pageset = alloc_percpu(struct per_cpu_pageset);
-	for_each_possible_cpu(cpu)
-		zone_pageset_init(zone, cpu);
+	for_each_possible_cpu(cpu) {
+		p = per_cpu_ptr(zone->pageset, cpu);
+		pageset_init(p);
+	}
+
+	zone_set_pageset_high_and_batch(zone);
 }
 
 /*
@@ -8002,15 +8005,6 @@ int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *table, int write,
 	return 0;
 }
 
-static void __zone_pcp_update(struct zone *zone)
-{
-	unsigned int cpu;
-
-	for_each_possible_cpu(cpu)
-		pageset_set_high_and_batch(zone,
-				per_cpu_ptr(zone->pageset, cpu));
-}
-
 /*
  * percpu_pagelist_fraction - changes the pcp->high for each zone on each
  * cpu.  It is the fraction of total pages in each zone that a hot per cpu
@@ -8043,7 +8037,7 @@ int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *table, int write,
 		goto out;
 
 	for_each_populated_zone(zone)
-		__zone_pcp_update(zone);
+		zone_set_pageset_high_and_batch(zone);
 out:
 	mutex_unlock(&pcp_batch_high_lock);
 	return ret;
@@ -8659,7 +8653,7 @@ EXPORT_SYMBOL(free_contig_range);
 void __meminit zone_pcp_update(struct zone *zone)
 {
 	mutex_lock(&pcp_batch_high_lock);
-	__zone_pcp_update(zone);
+	zone_set_pageset_high_and_batch(zone);
 	mutex_unlock(&pcp_batch_high_lock);
 }
 
-- 
2.28.0