Move remote node draining out of slab allocators

Currently the slab allocators contain callbacks into the page allocator to
perform the draining of pagesets on remote nodes.  This requires SLUB to have
a whole subsystem in order to be compatible with SLAB.  Moving node draining
out of the slab allocators avoids a section of code in SLUB.

Move the node draining so that is is done when the vm statistics are updated.
At that point we are already touching all the cachelines with the pagesets of
a processor.

Add a expire counter there.  If we have to update per zone or global vm
statistics then assume that the pageset will require subsequent draining.

The expire counter will be decremented on each vm stats update pass until it
reaches zero.  Then we will drain one batch from the pageset.  The draining
will cause vm counter updates which will then cause another expiration until
the pcp is empty.  So we will drain a batch every 3 seconds.

Note that remote node draining is a somewhat esoteric feature that is required
on large NUMA systems because otherwise significant portions of system memory
can become trapped in pcp queues.  The number of pcp is determined by the
number of processors and nodes in a system.  A system with 4 processors and 2
nodes has 8 pcps which is okay.  But a system with 1024 processors and 512
nodes has 512k pcps with a high potential for large amount of memory being
caught in them.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Christoph Lameter

include/linux/gfp.h

@@ -176,10 +176,6 @@ extern void FASTCALL(free_cold_page(struct page *page));
 #define free_page(addr) free_pages((addr),0)
 
 void page_alloc_init(void);
-#ifdef CONFIG_NUMA
-void drain_node_pages(int node);
-#else
-static inline void drain_node_pages(int node) { };
-#endif
+void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp);
 
 #endif /* __LINUX_GFP_H */

include/linux/mmzone.h

@@ -83,6 +83,9 @@ struct per_cpu_pages {
 
 struct per_cpu_pageset {
 	struct per_cpu_pages pcp[2];	/* 0: hot.  1: cold */
+#ifdef CONFIG_NUMA
+	s8 expire;
+#endif
 #ifdef CONFIG_SMP
 	s8 stat_threshold;
 	s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];

mm/page_alloc.c

@@ -691,43 +691,26 @@ static void __init setup_nr_node_ids(void) {}
 
 #ifdef CONFIG_NUMA
 /*
- * Called from the slab reaper to drain pagesets on a particular node that
- * belongs to the currently executing processor.
+ * Called from the vmstat counter updater to drain pagesets of this
+ * currently executing processor on remote nodes after they have
+ * expired.
+ *
  * Note that this function must be called with the thread pinned to
  * a single processor.
  */
-void drain_node_pages(int nodeid)
+void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
 {
-	int i;
-	enum zone_type z;
 	unsigned long flags;
+	int to_drain;
 
-	for (z = 0; z < MAX_NR_ZONES; z++) {
-		struct zone *zone = NODE_DATA(nodeid)->node_zones + z;
-		struct per_cpu_pageset *pset;
-
-		if (!populated_zone(zone))
-			continue;
-
-		pset = zone_pcp(zone, smp_processor_id());
-		for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
-			struct per_cpu_pages *pcp;
-
-			pcp = &pset->pcp[i];
-			if (pcp->count) {
-				int to_drain;
-
-				local_irq_save(flags);
-				if (pcp->count >= pcp->batch)
-					to_drain = pcp->batch;
-				else
-					to_drain = pcp->count;
-				free_pages_bulk(zone, to_drain, &pcp->list, 0);
-				pcp->count -= to_drain;
-				local_irq_restore(flags);
-			}
-		}
-	}
+	local_irq_save(flags);
+	if (pcp->count >= pcp->batch)
+		to_drain = pcp->batch;
+	else
+		to_drain = pcp->count;
+	free_pages_bulk(zone, to_drain, &pcp->list, 0);
+	pcp->count -= to_drain;
+	local_irq_restore(flags);
 }
 #endif
 

mm/slab.c

@@ -928,12 +928,6 @@ static void next_reap_node(void)
 {
 	int node = __get_cpu_var(reap_node);
 
-	/*
-	 * Also drain per cpu pages on remote zones
-	 */
-	if (node != numa_node_id())
-		drain_node_pages(node);
-
 	node = next_node(node, node_online_map);
 	if (unlikely(node >= MAX_NUMNODES))
 		node = first_node(node_online_map);

mm/slub.c

@@ -2530,90 +2530,6 @@ static struct notifier_block __cpuinitdata slab_notifier =
 
 #endif
 
-#ifdef CONFIG_NUMA
-
-/*****************************************************************
- * Generic reaper used to support the page allocator
- * (the cpu slabs are reaped by a per slab workqueue).
- *
- * Maybe move this to the page allocator?
- ****************************************************************/
-
-static DEFINE_PER_CPU(unsigned long, reap_node);
-
-static void init_reap_node(int cpu)
-{
-	int node;
-
-	node = next_node(cpu_to_node(cpu), node_online_map);
-	if (node == MAX_NUMNODES)
-		node = first_node(node_online_map);
-
-	__get_cpu_var(reap_node) = node;
-}
-
-static void next_reap_node(void)
-{
-	int node = __get_cpu_var(reap_node);
-
-	/*
-	 * Also drain per cpu pages on remote zones
-	 */
-	if (node != numa_node_id())
-		drain_node_pages(node);
-
-	node = next_node(node, node_online_map);
-	if (unlikely(node >= MAX_NUMNODES))
-		node = first_node(node_online_map);
-	__get_cpu_var(reap_node) = node;
-}
-#else
-#define init_reap_node(cpu) do { } while (0)
-#define next_reap_node(void) do { } while (0)
-#endif
-
-#define REAPTIMEOUT_CPUC	(2*HZ)
-
-#ifdef CONFIG_SMP
-static DEFINE_PER_CPU(struct delayed_work, reap_work);
-
-static void cache_reap(struct work_struct *unused)
-{
-	next_reap_node();
-	schedule_delayed_work(&__get_cpu_var(reap_work),
-				      REAPTIMEOUT_CPUC);
-}
-
-static void __devinit start_cpu_timer(int cpu)
-{
-	struct delayed_work *reap_work = &per_cpu(reap_work, cpu);
-
-	/*
-	 * When this gets called from do_initcalls via cpucache_init(),
-	 * init_workqueues() has already run, so keventd will be setup
-	 * at that time.
-	 */
-	if (keventd_up() && reap_work->work.func == NULL) {
-		init_reap_node(cpu);
-		INIT_DELAYED_WORK(reap_work, cache_reap);
-		schedule_delayed_work_on(cpu, reap_work, HZ + 3 * cpu);
-	}
-}
-
-static int __init cpucache_init(void)
-{
-	int cpu;
-
-	/*
-	 * Register the timers that drain pcp pages and update vm statistics
-	 */
-	for_each_online_cpu(cpu)
-		start_cpu_timer(cpu);
-	return 0;
-}
-__initcall(cpucache_init);
-#endif
-
 void *__kmalloc_track_caller(size_t size, gfp_t gfpflags, void *caller)
 {
 	struct kmem_cache *s = get_slab(size, gfpflags);

mm/vmstat.c

@@ -281,6 +281,17 @@ EXPORT_SYMBOL(dec_zone_page_state);
 
 /*
  * Update the zone counters for one cpu.
+ *
+ * Note that refresh_cpu_vm_stats strives to only access
+ * node local memory. The per cpu pagesets on remote zones are placed
+ * in the memory local to the processor using that pageset. So the
+ * loop over all zones will access a series of cachelines local to
+ * the processor.
+ *
+ * The call to zone_page_state_add updates the cachelines with the
+ * statistics in the remote zone struct as well as the global cachelines
+ * with the global counters. These could cause remote node cache line
+ * bouncing and will have to be only done when necessary.
  */
 void refresh_cpu_vm_stats(int cpu)
 {
@@ -289,21 +300,54 @@ void refresh_cpu_vm_stats(int cpu)
 	unsigned long flags;
 
 	for_each_zone(zone) {
-		struct per_cpu_pageset *pcp;
+		struct per_cpu_pageset *p;
 
 		if (!populated_zone(zone))
 			continue;
 
-		pcp = zone_pcp(zone, cpu);
+		p = zone_pcp(zone, cpu);
 
 		for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
-			if (pcp->vm_stat_diff[i]) {
+			if (p->vm_stat_diff[i]) {
 				local_irq_save(flags);
-				zone_page_state_add(pcp->vm_stat_diff[i],
+				zone_page_state_add(p->vm_stat_diff[i],
 					zone, i);
-				pcp->vm_stat_diff[i] = 0;
+				p->vm_stat_diff[i] = 0;
+#ifdef CONFIG_NUMA
+				/* 3 seconds idle till flush */
+				p->expire = 3;
+#endif
 				local_irq_restore(flags);
 			}
+#ifdef CONFIG_NUMA
+		/*
+		 * Deal with draining the remote pageset of this
+		 * processor
+		 *
+		 * Check if there are pages remaining in this pageset
+		 * if not then there is nothing to expire.
+		 */
+		if (!p->expire || (!p->pcp[0].count && !p->pcp[1].count))
+			continue;
+
+		/*
+		 * We never drain zones local to this processor.
+		 */
+		if (zone_to_nid(zone) == numa_node_id()) {
+			p->expire = 0;
+			continue;
+		}
+
+		p->expire--;
+		if (p->expire)
+			continue;
+
+		if (p->pcp[0].count)
+			drain_zone_pages(zone, p->pcp + 0);
+
+		if (p->pcp[1].count)
+			drain_zone_pages(zone, p->pcp + 1);
+#endif
 	}
 }