[PATCH 18/22] mm: page allocator: Split magazine lock in two to reduce contention

Mel Gorman
2013-05-08T16:05:20Z

This is the simpliest example of how the lock can be split arbitrarily
on a boundary. Ideally it would be based on SMT characteristics but lets
just split it in two to start with and prefer a magazine based on the
processor ID.

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
include/linux/mmzone.h | 12 ++++--
mm/page_alloc.c | 114 +++++++++++++++++++++++++++++++++++--------------
mm/vmstat.c | 8 ++--
3 files changed, 95 insertions(+), 39 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 4eb5151..c0a8958 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -90,6 +90,11 @@ struct free_area_magazine {
unsigned long nr_free;
};

+struct free_magazine {
+ spinlock_t lock;
+ struct free_area_magazine area;
+};
+
struct pglist_data;

/*
@@ -305,6 +310,8 @@ enum zone_type {

#ifndef __GENERATING_BOUNDS_H

+#define NR_MAGAZINES 2
+
struct zone {
/* Fields commonly accessed by the page allocator */

@@ -368,10 +375,9 @@ struct zone {

/*
* Keep some order-0 pages on a separate free list
- * protected by an irq-unsafe lock
+ * protected by an irq-unsafe lock.
*/
- spinlock_t _magazine_lock;
- struct free_area_magazine _noirq_magazine;
+ struct free_magazine noirq_magazine[NR_MAGAZINES];

#ifndef CONFIG_SPARSEMEM
/*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 36ffff0..63952f6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1074,33 +1074,76 @@ void mark_free_pages(struct zone *zone)
#define MAGAZINE_ALLOC_BATCH (384)
#define MAGAZINE_FREE_BATCH (64)

-static inline struct free_area_magazine *find_lock_magazine(struct zone *zone)
+static inline struct free_magazine *lock_magazine(struct zone *zone)
{
- struct free_area_magazine *area = &zone->_noirq_magazine;
- spin_lock(&zone->_magazine_lock);
- return area;
+ int i = (raw_smp_processor_id() >> 1) & (NR_MAGAZINES-1);
+ spin_lock(&zone->noirq_magazine[i].lock);
+ return &zone->noirq_magazine[i];
}

-static inline struct free_area_magazine *find_lock_filled_magazine(struct zone *zone)
+static inline struct free_magazine *find_lock_magazine(struct zone *zone)
{
- struct free_area_magazine *area = &zone->_noirq_magazine;
- if (!area->nr_free)
+ int i = (raw_smp_processor_id() >> 1) & (NR_MAGAZINES-1);
+ int start = i;
+
+ do {
+ if (spin_trylock(&zone->noirq_magazine[i].lock))
+ goto out;
+ i = (i + 1) & (NR_MAGAZINES-1);
+ } while (i != start);
+
+ spin_lock(&zone->noirq_magazine[i].lock);
+out:
+ return &zone->noirq_magazine[i];
+}
+
+static struct free_magazine *find_lock_filled_magazine(struct zone *zone)
+{
+ int i = (raw_smp_processor_id() >> 1) & (NR_MAGAZINES-1);
+ int start = i;
+ bool all_empty = true;
+
+ /* Pass 1. Find an unlocked magazine with free pages */
+ do {
+ if (zone->noirq_magazine[i].area.nr_free) {
+ all_empty = false;
+ if (spin_trylock(&zone->noirq_magazine[i].lock))
+ goto out;
+ }
+ i = (i + 1) & (NR_MAGAZINES-1);
+ } while (i != start);
+
+ /* If all area empty then a second pass is pointness */
+ if (all_empty)
return NULL;
- spin_lock(&zone->_magazine_lock);
- return area;
+
+ /* Pass 2. Find a magazine with pages and wait on it */
+ do {
+ if (zone->noirq_magazine[i].area.nr_free) {
+ spin_lock(&zone->noirq_magazine[i].lock);
+ goto out;
+ }
+ i = (i + 1) & (NR_MAGAZINES-1);
+ } while (i != start);
+
+ /* Lock holder emptied the last magazine or raced */
+ return NULL;
+
+out:
+ return &zone->noirq_magazine[i];
}

-static inline void unlock_magazine(struct free_area_magazine *area)
+static inline void unlock_magazine(struct free_magazine *mag)
{
- struct zone *zone = container_of(area, struct zone, _noirq_magazine);
- spin_unlock(&zone->_magazine_lock);
+ spin_unlock(&mag->lock);
}

static
-struct page *__rmqueue_magazine(struct free_area_magazine *area,
+struct page *__rmqueue_magazine(struct free_magazine *mag,
int migratetype)
{
struct page *page;
+ struct free_area_magazine *area = &mag->area;

if (list_empty(&area->free_list[migratetype]))
return NULL;
@@ -1114,7 +1157,7 @@ struct page *__rmqueue_magazine(struct free_area_magazine *area,
return page;
}

-static void magazine_drain(struct zone *zone, struct free_area_magazine *area,
+static void magazine_drain(struct zone *zone, struct free_magazine *mag,
int migratetype)
{
struct list_head *list;
@@ -1123,10 +1166,11 @@ static void magazine_drain(struct zone *zone, struct free_area_magazine *area,
unsigned int to_free = MAGAZINE_FREE_BATCH;
unsigned int nr_freed_cma = 0;
unsigned long flags;
+ struct free_area_magazine *area = &mag->area;
LIST_HEAD(free_list);

if (area->nr_free < MAGAZINE_LIMIT) {
- unlock_magazine(area);
+ unlock_magazine(mag);
return;
}

@@ -1161,7 +1205,7 @@ static void magazine_drain(struct zone *zone, struct free_area_magazine *area,
}

/* Free the list of pages to the buddy allocator */
- unlock_magazine(area);
+ unlock_magazine(mag);
spin_lock_irqsave(&zone->lock, flags);
while (!list_empty(&free_list)) {
page = list_entry(free_list.prev, struct page, lru);
@@ -1179,8 +1223,8 @@ static void magazine_drain(struct zone *zone, struct free_area_magazine *area,
void free_base_page(struct page *page)
{
struct zone *zone = page_zone(page);
+ struct free_magazine *mag;
int migratetype;
- struct free_area_magazine *area;

if (!free_pages_prepare(page, 0))
return;
@@ -1210,12 +1254,12 @@ void free_base_page(struct page *page)
}

/* Put the free page on the magazine list */
- area = find_lock_magazine(zone);
- list_add(&page->lru, &area->free_list[migratetype]);
- area->nr_free++;
+ mag = lock_magazine(zone);
+ list_add(&page->lru, &mag->area.free_list[migratetype]);
+ mag->area.nr_free++;

/* Drain the magazine if necessary, releases the magazine lock */
- magazine_drain(zone, area, migratetype);
+ magazine_drain(zone, mag, migratetype);
}

/* Free a list of 0-order pages */
@@ -1328,12 +1372,12 @@ static
struct page *rmqueue_magazine(struct zone *zone, int migratetype)
{
struct page *page = NULL;
- struct free_area_magazine *area = find_lock_filled_magazine(zone);
+ struct free_magazine *mag = find_lock_filled_magazine(zone);

retry:
- if (area) {
- page = __rmqueue_magazine(area, migratetype);
- unlock_magazine(area);
+ if (mag) {
+ page = __rmqueue_magazine(mag, migratetype);
+ unlock_magazine(mag);
}

/* Try refilling the magazine on allocaion failure */
@@ -1359,9 +1403,9 @@ retry:
if (!nr_alloced)
return NULL;

- area = find_lock_magazine(zone);
- list_splice(&alloc_list, &area->free_list[migratetype]);
- area->nr_free += nr_alloced;
+ mag = find_lock_magazine(zone);
+ list_splice(&alloc_list, &mag->area.free_list[migratetype]);
+ mag->area.nr_free += nr_alloced;
goto retry;
}

@@ -3797,12 +3841,14 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,

static void __meminit zone_init_free_lists(struct zone *zone)
{
- unsigned int order, t;
+ unsigned int order, t, i;
for_each_migratetype_order(order, t) {
INIT_LIST_HEAD(&zone->free_area[order].free_list[t]);
zone->free_area[order].nr_free = 0;
- INIT_LIST_HEAD(&zone->_noirq_magazine.free_list[t]);
- zone->_noirq_magazine.nr_free = 0;
+ for (i = 0; i < NR_MAGAZINES && t < MIGRATE_PCPTYPES; i++) {
+ INIT_LIST_HEAD(&zone->noirq_magazine[i].area.free_list[t]);
+ zone->noirq_magazine[i].area.nr_free = 0;
+ }
}
}

@@ -4284,7 +4330,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
enum zone_type j;
int nid = pgdat->node_id;
unsigned long zone_start_pfn = pgdat->node_start_pfn;
- int ret;
+ int ret, i;

pgdat_resize_init(pgdat);
#ifdef CONFIG_NUMA_BALANCING
@@ -4352,7 +4398,9 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
zone->name = zone_names[j];
spin_lock_init(&zone->lock);
spin_lock_init(&zone->lru_lock);
- spin_lock_init(&zone->_magazine_lock);
+
+ for (i = 0; i < NR_MAGAZINES; i++)
+ spin_lock_init(&zone->noirq_magazine[i].lock);
zone_seqlock_init(zone);
zone->zone_pgdat = pgdat;

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3db0d52..1374f92 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1002,9 +1002,11 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
seq_printf(m,
")"
"\n noirq magazine");
- seq_printf(m,
- "\n count: %lu",
- zone->_noirq_magazine.nr_free);
+ for (i = 0; i < NR_MAGAZINES; i++) {
+ seq_printf(m,
+ "\n count: %lu",
+ zone->noirq_magazine[i].area.nr_free);
+ }

#ifdef CONFIG_SMP
for_each_online_cpu(i) {
--
1.8.1.4