Page allocator: get rid of the list of cold pages

We have repeatedly discussed if the cold pages still have a point. There is
one way to join the two lists: Use a single list and put the cold pages at the
end and the hot pages at the beginning. That way a single list can serve for
both types of allocations.

The discussion of the RFC for this and Mel's measurements indicate that
there may not be too much of a point left to having separate lists for
hot and cold pages (see http://marc.info/?t=119492914200001&r=1&w=2).
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Martin Bligh <mbligh@mbligh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -113,7 +113,7 @@ struct per_cpu_pages {
 };
 
 struct per_cpu_pageset {
-	struct per_cpu_pages pcp[2];	/* 0: hot.  1: cold */
+	struct per_cpu_pages pcp;
 #ifdef CONFIG_NUMA
 	s8 expire;
 #endif

mm/page_alloc.c

@@ -901,25 +901,22 @@ static void drain_pages(unsigned int cpu)
 {
 	unsigned long flags;
 	struct zone *zone;
-	int i;
 
 	for_each_zone(zone) {
 		struct per_cpu_pageset *pset;
+		struct per_cpu_pages *pcp;
 
 		if (!populated_zone(zone))
 			continue;
 
 		pset = zone_pcp(zone, cpu);
-		for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
-			struct per_cpu_pages *pcp;
 
-			pcp = &pset->pcp[i];
+		pcp = &pset->pcp;
 		local_irq_save(flags);
 		free_pages_bulk(zone, pcp->count, &pcp->list, 0);
 		pcp->count = 0;
 		local_irq_restore(flags);
 	}
-	}
 }
 
 /*
@@ -993,9 +990,12 @@ static void fastcall free_hot_cold_page(struct page *page, int cold)
 	arch_free_page(page, 0);
 	kernel_map_pages(page, 1, 0);
 
-	pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
+	pcp = &zone_pcp(zone, get_cpu())->pcp;
 	local_irq_save(flags);
 	__count_vm_event(PGFREE);
+	if (cold)
+		list_add_tail(&page->lru, &pcp->list);
+	else
 		list_add(&page->lru, &pcp->list);
 	set_page_private(page, get_pageblock_migratetype(page));
 	pcp->count++;
@@ -1054,7 +1054,7 @@ again:
 	if (likely(order == 0)) {
 		struct per_cpu_pages *pcp;
 
-		pcp = &zone_pcp(zone, cpu)->pcp[cold];
+		pcp = &zone_pcp(zone, cpu)->pcp;
 		local_irq_save(flags);
 		if (!pcp->count) {
 			pcp->count = rmqueue_bulk(zone, 0,
@@ -1064,9 +1064,15 @@ again:
 		}
 
 		/* Find a page of the appropriate migrate type */
+		if (cold) {
+			list_for_each_entry_reverse(page, &pcp->list, lru)
+				if (page_private(page) == migratetype)
+					break;
+		} else {
 			list_for_each_entry(page, &pcp->list, lru)
 				if (page_private(page) == migratetype)
 					break;
+		}
 
 		/* Allocate more to the pcp list if necessary */
 		if (unlikely(&page->lru == &pcp->list)) {
@@ -1793,12 +1799,9 @@ void show_free_areas(void)
 
 			pageset = zone_pcp(zone, cpu);
 
-			printk("CPU %4d: Hot: hi:%5d, btch:%4d usd:%4d   "
-			       "Cold: hi:%5d, btch:%4d usd:%4d\n",
-			       cpu, pageset->pcp[0].high,
-			       pageset->pcp[0].batch, pageset->pcp[0].count,
-			       pageset->pcp[1].high, pageset->pcp[1].batch,
-			       pageset->pcp[1].count);
+			printk("CPU %4d: hi:%5d, btch:%4d usd:%4d\n",
+			       cpu, pageset->pcp.high,
+			       pageset->pcp.batch, pageset->pcp.count);
 		}
 	}
 
@@ -2596,17 +2599,11 @@ inline void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
 
 	memset(p, 0, sizeof(*p));
 
-	pcp = &p->pcp[0];		/* hot */
+	pcp = &p->pcp;
 	pcp->count = 0;
 	pcp->high = 6 * batch;
 	pcp->batch = max(1UL, 1 * batch);
 	INIT_LIST_HEAD(&pcp->list);
-
-	pcp = &p->pcp[1];		/* cold*/
-	pcp->count = 0;
-	pcp->high = 2 * batch;
-	pcp->batch = max(1UL, batch/2);
-	INIT_LIST_HEAD(&pcp->list);
 }
 
 /*
@@ -2619,7 +2616,7 @@ static void setup_pagelist_highmark(struct per_cpu_pageset *p,
 {
 	struct per_cpu_pages *pcp;
 
-	pcp = &p->pcp[0]; /* hot list */
+	pcp = &p->pcp;
 	pcp->high = high;
 	pcp->batch = max(1UL, high/4);
 	if ((high/4) > (PAGE_SHIFT * 8))

mm/vmstat.c

@@ -337,7 +337,7 @@ void refresh_cpu_vm_stats(int cpu)
 		 * 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))
+		if (!p->expire || !p->pcp.count)
 			continue;
 
 		/*
@@ -352,11 +352,8 @@ void refresh_cpu_vm_stats(int cpu)
 		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);
+		if (p->pcp.count)
+			drain_zone_pages(zone, &p->pcp);
 #endif
 	}
 
@@ -693,20 +690,17 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		   "\n  pagesets");
 	for_each_online_cpu(i) {
 		struct per_cpu_pageset *pageset;
-		int j;
 
 		pageset = zone_pcp(zone, i);
-		for (j = 0; j < ARRAY_SIZE(pageset->pcp); j++) {
 		seq_printf(m,
-				   "\n    cpu: %i pcp: %i"
+			   "\n    cpu: %i"
 			   "\n              count: %i"
 			   "\n              high:  %i"
 			   "\n              batch: %i",
-				   i, j,
-				   pageset->pcp[j].count,
-				   pageset->pcp[j].high,
-				   pageset->pcp[j].batch);
-			}
+			   i,
+			   pageset->pcp.count,
+			   pageset->pcp.high,
+			   pageset->pcp.batch);
 #ifdef CONFIG_SMP
 		seq_printf(m, "\n  vm stats threshold: %d",
 				pageset->stat_threshold);