mm: page_alloc: introduce MIGRATE_FREE

To cut down on type mixing, put empty pageblocks on separate freelists
and make them the first fallback preference before stealing space from
incompatible blocks.

The neutral block designation will also be handy in subsequent patches
that simplify compaction, add per-mt freelist counts and make
compaction_suitable() more precise, and ultimately make pageblocks the
basis of free memory management.

Signed-off-by: Johannes Weiner <[email protected]>

include/linux/mmzone.h

@@ -45,6 +45,7 @@ enum migratetype {
 	MIGRATE_RECLAIMABLE,
 	MIGRATE_PCPTYPES,	/* the number of types on the pcp lists */
 	MIGRATE_HIGHATOMIC = MIGRATE_PCPTYPES,
+	MIGRATE_FREE,
 #ifdef CONFIG_CMA
 	/*
 	 * MIGRATE_CMA migration type is designed to mimic the way
@@ -88,7 +89,7 @@ static inline bool is_migrate_movable(int mt)
  */
 static inline bool migratetype_is_mergeable(int mt)
 {
-	return mt < MIGRATE_PCPTYPES;
+	return mt < MIGRATE_PCPTYPES || mt == MIGRATE_FREE;
 }
 
 #define for_each_migratetype_order(order, type) \

mm/memory_hotplug.c

@@ -1129,7 +1129,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 		build_all_zonelists(NULL);
 
 	/* Basic onlining is complete, allow allocation of onlined pages. */
-	undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
+	undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_FREE);
 
 	/*
 	 * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
@@ -1951,7 +1951,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 
 failed_removal_isolated:
 	/* pushback to free area */
-	undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
+	undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_FREE);
 	memory_notify(MEM_CANCEL_OFFLINE, &arg);
 failed_removal_pcplists_disabled:
 	lru_cache_enable();

mm/page_alloc.c

@@ -380,6 +380,7 @@ const char * const migratetype_names[MIGRATE_TYPES] = {
 	"Movable",
 	"Reclaimable",
 	"HighAtomic",
+	"Free",
 #ifdef CONFIG_CMA
 	"CMA",
 #endif
@@ -1222,6 +1223,13 @@ static inline void __free_one_page(struct page *page,
 done_merging:
 	set_buddy_order(page, order);
 
+	/* If we freed one or normal page blocks, mark them free. */
+	if (unlikely(order >= pageblock_order &&
+		     migratetype_is_mergeable(migratetype))) {
+		change_pageblock_range(page, order, MIGRATE_FREE);
+		migratetype = MIGRATE_FREE;
+	}
+
 	if (fpi_flags & FPI_TO_TAIL)
 		to_tail = true;
 	else if (is_shuffle_order(order))
@@ -1961,14 +1969,14 @@ static void __init deferred_free_range(unsigned long pfn,
 
 	/* Free a large naturally-aligned chunk if possible */
 	if (nr_pages == pageblock_nr_pages && pageblock_aligned(pfn)) {
-		set_pageblock_migratetype(page, MIGRATE_MOVABLE);
+		set_pageblock_migratetype(page, MIGRATE_FREE);
 		__free_pages_core(page, pageblock_order);
 		return;
 	}
 
 	for (i = 0; i < nr_pages; i++, page++, pfn++) {
 		if (pageblock_aligned(pfn))
-			set_pageblock_migratetype(page, MIGRATE_MOVABLE);
+			set_pageblock_migratetype(page, MIGRATE_FREE);
 		__free_pages_core(page, 0);
 	}
 }
@@ -2612,10 +2620,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
  *
  * The other migratetypes do not have fallbacks.
  */
-static int fallbacks[MIGRATE_TYPES][3] = {
-	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_TYPES },
-	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
-	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_TYPES },
+static int fallbacks[MIGRATE_TYPES][4] = {
+	[MIGRATE_UNMOVABLE]   = { MIGRATE_FREE, MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_TYPES },
+	[MIGRATE_MOVABLE]     = { MIGRATE_FREE, MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
+	[MIGRATE_RECLAIMABLE] = { MIGRATE_FREE, MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_TYPES },
 };
 
 #ifdef CONFIG_CMA
@@ -2705,8 +2713,13 @@ int move_freepages_block(struct zone *zone, struct page *page,
  * is worse than movable allocations stealing from unmovable and reclaimable
  * pageblocks.
  */
-static bool can_steal_fallback(unsigned int order, int start_mt)
+static bool can_steal_fallback(unsigned int order, int start_mt,
+			       int fallback_mt)
 {
+	/* The first allocation in a free block *must* claim it. */
+	if (fallback_mt == MIGRATE_FREE)
+		return true;
+
 	/*
 	 * Leaving this order check is intended, although there is
 	 * relaxed order check in next check. The reason is that
@@ -2808,6 +2821,21 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
 	free_pages = move_freepages_block(zone, page, old_block_type,
 					  start_type, &movable_pages);
 
+	/*
+	 * If we fell back into a free block, claim the whole thing
+	 */
+	if (old_block_type == MIGRATE_FREE) {
+		set_pageblock_migratetype(page, start_type);
+		if (!free_pages) {
+			/*
+			 * This can leave some non-FREE pages on the
+			 * FREE list. Future fallbacks will get them.
+			 */
+			goto single_page;
+		}
+		return;
+	}
+
 	/*
 	 * Determine how many pages are compatible with our allocation.
 	 * For movable allocation, it's the number of movable pages which
@@ -2873,7 +2901,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
 		if (free_area_empty(area, fallback_mt))
 			continue;
 
-		if (can_steal_fallback(order, migratetype))
+		if (can_steal_fallback(order, migratetype, fallback_mt))
 			*can_steal = true;
 
 		if (!only_stealable)
@@ -3485,7 +3513,7 @@ void free_unref_page(struct page *page, unsigned int order)
 	 */
 	migratetype = get_pcppage_migratetype(page);
 	if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
-		if (unlikely(is_migrate_isolate(migratetype))) {
+		if (unlikely(is_migrate_isolate(migratetype) || migratetype == MIGRATE_FREE)) {
 			free_one_page(page_zone(page), page, pfn, order, migratetype, FPI_NONE);
 			return;
 		}
@@ -3529,7 +3557,7 @@ void free_unref_page_list(struct list_head *list)
 		 * comment in free_unref_page.
 		 */
 		migratetype = get_pcppage_migratetype(page);
-		if (unlikely(is_migrate_isolate(migratetype))) {
+		if (unlikely(is_migrate_isolate(migratetype) || migratetype == MIGRATE_FREE)) {
 			list_del(&page->lru);
 			free_one_page(page_zone(page), page, pfn, 0, migratetype, FPI_NONE);
 			continue;
@@ -3632,10 +3660,10 @@ int __isolate_free_page(struct page *page, unsigned int order)
 	del_page_from_free_list(page, zone, order, mt);
 
 	/*
-	 * Set the pageblock if the isolated page is at least half of a
-	 * pageblock
+	 * Set the pageblock if the isolated page is from a free block
+	 * or at least half of a pageblock
 	 */
-	if (order >= pageblock_order - 1) {
+	if (mt == MIGRATE_FREE || order >= pageblock_order - 1) {
 		struct page *endpage = page + (1 << order) - 1;
 		for (; page < endpage; page += pageblock_nr_pages) {
 			int mt = get_pageblock_migratetype(page);
@@ -4020,6 +4048,9 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 		if (!area->nr_free)
 			continue;
 
+		if (!free_area_empty(area, MIGRATE_FREE))
+			return true;
+
 		for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) {
 			if (!free_area_empty(area, mt))
 				return true;
@@ -6073,6 +6104,7 @@ static void show_migration_types(unsigned char type)
 		[MIGRATE_MOVABLE]	= 'M',
 		[MIGRATE_RECLAIMABLE]	= 'E',
 		[MIGRATE_HIGHATOMIC]	= 'H',
+		[MIGRATE_FREE]		= 'F',
 #ifdef CONFIG_CMA
 		[MIGRATE_CMA]		= 'C',
 #endif
@@ -7017,7 +7049,7 @@ static void __init memmap_init_zone_range(struct zone *zone,
 		return;
 
 	memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn,
-			  zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
+			  zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_FREE);
 
 	if (*hole_pfn < start_pfn)
 		init_unavailable_range(*hole_pfn, start_pfn, zone_id, nid);
@@ -9414,8 +9446,7 @@ static int __alloc_contig_pages(unsigned long start_pfn,
 {
 	unsigned long end_pfn = start_pfn + nr_pages;
 
-	return alloc_contig_range(start_pfn, end_pfn, MIGRATE_MOVABLE,
-				  gfp_mask);
+	return alloc_contig_range(start_pfn, end_pfn, MIGRATE_FREE, gfp_mask);
 }
 
 static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,