[PATCH] mm: page_state opt

Optimise page_state manipulations by introducing interrupt unsafe accessors
to page_state fields.  Callers must provide their own locking (either
disable interrupts or not update from interrupt context).

Switch over the hot callsites that can easily be moved under interrupts off
sections.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 72 insertions, 54 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7f58077..fd47494 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -424,9 +424,9 @@ void __free_pages_ok(struct page *page, unsigned int order)
 		return;
 
 	list_add(&page->lru, &list);
-	mod_page_state(pgfree, 1 << order);
 	kernel_map_pages(page, 1<<order, 0);
 	local_irq_save(flags);
+	__mod_page_state(pgfree, 1 << order);
 	free_pages_bulk(page_zone(page), 1, &list, order);
 	local_irq_restore(flags);
 }
@@ -674,18 +674,14 @@ void drain_local_pages(void)
 }
 #endif /* CONFIG_PM */
 
-static void zone_statistics(struct zonelist *zonelist, struct zone *z)
+static void zone_statistics(struct zonelist *zonelist, struct zone *z, int cpu)
 {
 #ifdef CONFIG_NUMA
-	unsigned long flags;
-	int cpu;
 	pg_data_t *pg = z->zone_pgdat;
 	pg_data_t *orig = zonelist->zones[0]->zone_pgdat;
 	struct per_cpu_pageset *p;
 
-	local_irq_save(flags);
-	cpu = smp_processor_id();
-	p = zone_pcp(z,cpu);
+	p = zone_pcp(z, cpu);
 	if (pg == orig) {
 		p->numa_hit++;
 	} else {
@@ -696,7 +692,6 @@ static void zone_statistics(struct zonelist *zonelist, struct zone *z)
 		p->local_node++;
 	else
 		p->other_node++;
-	local_irq_restore(flags);
 #endif
 }
 
@@ -716,11 +711,11 @@ static void fastcall free_hot_cold_page(struct page *page, int cold)
 	if (free_pages_check(page))
 		return;
 
-	inc_page_state(pgfree);
 	kernel_map_pages(page, 1, 0);
 
 	pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
 	local_irq_save(flags);
+	__inc_page_state(pgfree);
 	list_add(&page->lru, &pcp->list);
 	pcp->count++;
 	if (pcp->count >= pcp->high)
@@ -753,49 +748,58 @@ static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
  * we cheat by calling it from here, in the order > 0 path.  Saves a branch
  * or two.
  */
-static struct page *
-buffered_rmqueue(struct zone *zone, int order, gfp_t gfp_flags)
+static struct page *buffered_rmqueue(struct zonelist *zonelist,
+			struct zone *zone, int order, gfp_t gfp_flags)
 {
 	unsigned long flags;
 	struct page *page;
 	int cold = !!(gfp_flags & __GFP_COLD);
+	int cpu;
 
 again:
+	cpu  = get_cpu();
 	if (order == 0) {
 		struct per_cpu_pages *pcp;
 
-		page = NULL;
-		pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
+		pcp = &zone_pcp(zone, cpu)->pcp[cold];
 		local_irq_save(flags);
-		if (!pcp->count)
+		if (!pcp->count) {
 			pcp->count += rmqueue_bulk(zone, 0,
 						pcp->batch, &pcp->list);
-		if (likely(pcp->count)) {
-			page = list_entry(pcp->list.next, struct page, lru);
-			list_del(&page->lru);
-			pcp->count--;
+			if (unlikely(!pcp->count))
+				goto failed;
 		}
-		local_irq_restore(flags);
-		put_cpu();
+		page = list_entry(pcp->list.next, struct page, lru);
+		list_del(&page->lru);
+		pcp->count--;
 	} else {
 		spin_lock_irqsave(&zone->lock, flags);
 		page = __rmqueue(zone, order);
-		spin_unlock_irqrestore(&zone->lock, flags);
+		spin_unlock(&zone->lock);
+		if (!page)
+			goto failed;
 	}
 
-	if (page != NULL) {
-		BUG_ON(bad_range(zone, page));
-		mod_page_state_zone(zone, pgalloc, 1 << order);
-		if (prep_new_page(page, order))
-			goto again;
+	__mod_page_state_zone(zone, pgalloc, 1 << order);
+	zone_statistics(zonelist, zone, cpu);
+	local_irq_restore(flags);
+	put_cpu();
 
-		if (gfp_flags & __GFP_ZERO)
-			prep_zero_page(page, order, gfp_flags);
+	BUG_ON(bad_range(zone, page));
+	if (prep_new_page(page, order))
+		goto again;
 
-		if (order && (gfp_flags & __GFP_COMP))
-			prep_compound_page(page, order);
-	}
+	if (gfp_flags & __GFP_ZERO)
+		prep_zero_page(page, order, gfp_flags);
+
+	if (order && (gfp_flags & __GFP_COMP))
+		prep_compound_page(page, order);
 	return page;
+
+failed:
+	local_irq_restore(flags);
+	put_cpu();
+	return NULL;
 }
 
 #define ALLOC_NO_WATERMARKS	0x01 /* don't check watermarks at all */
@@ -871,9 +875,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order,
 				continue;
 		}
 
-		page = buffered_rmqueue(*z, order, gfp_mask);
+		page = buffered_rmqueue(zonelist, *z, order, gfp_mask);
 		if (page) {
-			zone_statistics(zonelist, *z);
 			break;
 		}
 	} while (*(++z) != NULL);
@@ -1248,7 +1251,7 @@ void get_full_page_state(struct page_state *ret)
 	__get_page_state(ret, sizeof(*ret) / sizeof(unsigned long), &mask);
 }
 
-unsigned long __read_page_state(unsigned long offset)
+unsigned long read_page_state_offset(unsigned long offset)
 {
 	unsigned long ret = 0;
 	int cpu;
@@ -1262,18 +1265,26 @@ unsigned long __read_page_state(unsigned long offset)
 	return ret;
 }
 
-void __mod_page_state(unsigned long offset, unsigned long delta)
+void __mod_page_state_offset(unsigned long offset, unsigned long delta)
+{
+	void *ptr;
+
+	ptr = &__get_cpu_var(page_states);
+	*(unsigned long *)(ptr + offset) += delta;
+}
+EXPORT_SYMBOL(__mod_page_state_offset);
+
+void mod_page_state_offset(unsigned long offset, unsigned long delta)
 {
 	unsigned long flags;
-	void* ptr;
+	void *ptr;
 
 	local_irq_save(flags);
 	ptr = &__get_cpu_var(page_states);
-	*(unsigned long*)(ptr + offset) += delta;
+	*(unsigned long *)(ptr + offset) += delta;
 	local_irq_restore(flags);
 }
-
-EXPORT_SYMBOL(__mod_page_state);
+EXPORT_SYMBOL(mod_page_state_offset);
 
 void __get_zone_counts(unsigned long *active, unsigned long *inactive,
 			unsigned long *free, struct pglist_data *pgdat)
diff --git a/mm/rmap.c b/mm/rmap.c
index 4107f64..6f3f7db 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -451,7 +451,11 @@ static void __page_set_anon_rmap(struct page *page,
 
 	page->index = linear_page_index(vma, address);
 
-	inc_page_state(nr_mapped);
+	/*
+	 * nr_mapped state can be updated without turning off
+	 * interrupts because it is not modified via interrupt.
+	 */
+	__inc_page_state(nr_mapped);
 }
 
 /**
@@ -498,7 +502,7 @@ void page_add_file_rmap(struct page *page)
 	BUG_ON(!pfn_valid(page_to_pfn(page)));
 
 	if (atomic_inc_and_test(&page->_mapcount))
-		inc_page_state(nr_mapped);
+		__inc_page_state(nr_mapped);
 }
 
 /**
@@ -522,7 +526,7 @@ void page_remove_rmap(struct page *page)
 		 */
 		if (page_test_and_clear_dirty(page))
 			set_page_dirty(page);
-		dec_page_state(nr_mapped);
+		__dec_page_state(nr_mapped);
 	}
 }
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7681d8e..be8235f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -645,16 +645,17 @@ static void shrink_cache(struct zone *zone, struct scan_control *sc)
 			goto done;
 
 		max_scan -= nr_scan;
-		if (current_is_kswapd())
-			mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
-		else
-			mod_page_state_zone(zone, pgscan_direct, nr_scan);
 		nr_freed = shrink_list(&page_list, sc);
-		if (current_is_kswapd())
-			mod_page_state(kswapd_steal, nr_freed);
-		mod_page_state_zone(zone, pgsteal, nr_freed);
 
-		spin_lock_irq(&zone->lru_lock);
+		local_irq_disable();
+		if (current_is_kswapd()) {
+			__mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
+			__mod_page_state(kswapd_steal, nr_freed);
+		} else
+			__mod_page_state_zone(zone, pgscan_direct, nr_scan);
+		__mod_page_state_zone(zone, pgsteal, nr_freed);
+
+		spin_lock(&zone->lru_lock);
 		/*
 		 * Put back any unfreeable pages.
 		 */
@@ -816,11 +817,13 @@ refill_inactive_zone(struct zone *zone, struct scan_control *sc)
 		}
 	}
 	zone->nr_active += pgmoved;
-	spin_unlock_irq(&zone->lru_lock);
-	pagevec_release(&pvec);
+	spin_unlock(&zone->lru_lock);
+
+	__mod_page_state_zone(zone, pgrefill, pgscanned);
+	__mod_page_state(pgdeactivate, pgdeactivate);
+	local_irq_enable();
 
-	mod_page_state_zone(zone, pgrefill, pgscanned);
-	mod_page_state(pgdeactivate, pgdeactivate);
+	pagevec_release(&pvec);
 }
 
 /*