1 files changed, 130 insertions, 8 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5888126..55e9c56 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1615,6 +1615,101 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
 	return -1;
 }
 
+/*
+ * Reserve a pageblock for exclusive use of high-order atomic allocations if
+ * there are no empty page blocks that contain a page with a suitable order
+ */
+static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
+				unsigned int alloc_order)
+{
+	int mt;
+	unsigned long max_managed, flags;
+
+	/*
+	 * Limit the number reserved to 1 pageblock or roughly 1% of a zone.
+	 * Check is race-prone but harmless.
+	 */
+	max_managed = (zone->managed_pages / 100) + pageblock_nr_pages;
+	if (zone->nr_reserved_highatomic >= max_managed)
+		return;
+
+	spin_lock_irqsave(&zone->lock, flags);
+
+	/* Recheck the nr_reserved_highatomic limit under the lock */
+	if (zone->nr_reserved_highatomic >= max_managed)
+		goto out_unlock;
+
+	/* Yoink! */
+	mt = get_pageblock_migratetype(page);
+	if (mt != MIGRATE_HIGHATOMIC &&
+			!is_migrate_isolate(mt) && !is_migrate_cma(mt)) {
+		zone->nr_reserved_highatomic += pageblock_nr_pages;
+		set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
+		move_freepages_block(zone, page, MIGRATE_HIGHATOMIC);
+	}
+
+out_unlock:
+	spin_unlock_irqrestore(&zone->lock, flags);
+}
+
+/*
+ * Used when an allocation is about to fail under memory pressure. This
+ * potentially hurts the reliability of high-order allocations when under
+ * intense memory pressure but failed atomic allocations should be easier
+ * to recover from than an OOM.
+ */
+static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
+{
+	struct zonelist *zonelist = ac->zonelist;
+	unsigned long flags;
+	struct zoneref *z;
+	struct zone *zone;
+	struct page *page;
+	int order;
+
+	for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->high_zoneidx,
+								ac->nodemask) {
+		/* Preserve at least one pageblock */
+		if (zone->nr_reserved_highatomic <= pageblock_nr_pages)
+			continue;
+
+		spin_lock_irqsave(&zone->lock, flags);
+		for (order = 0; order < MAX_ORDER; order++) {
+			struct free_area *area = &(zone->free_area[order]);
+
+			if (list_empty(&area->free_list[MIGRATE_HIGHATOMIC]))
+				continue;
+
+			page = list_entry(area->free_list[MIGRATE_HIGHATOMIC].next,
+						struct page, lru);
+
+			/*
+			 * It should never happen but changes to locking could
+			 * inadvertently allow a per-cpu drain to add pages
+			 * to MIGRATE_HIGHATOMIC while unreserving so be safe
+			 * and watch for underflows.
+			 */
+			zone->nr_reserved_highatomic -= min(pageblock_nr_pages,
+				zone->nr_reserved_highatomic);
+
+			/*
+			 * Convert to ac->migratetype and avoid the normal
+			 * pageblock stealing heuristics. Minimally, the caller
+			 * is doing the work and needs the pages. More
+			 * importantly, if the block was always converted to
+			 * MIGRATE_UNMOVABLE or another type then the number
+			 * of pageblocks that cannot be completely freed
+			 * may increase.
+			 */
+			set_pageblock_migratetype(page, ac->migratetype);
+			move_freepages_block(zone, page, ac->migratetype);
+			spin_unlock_irqrestore(&zone->lock, flags);
+			return;
+		}
+		spin_unlock_irqrestore(&zone->lock, flags);
+	}
+}
+
 /* Remove an element from the buddy allocator from the fallback list */
 static inline struct page *
 __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
@@ -1670,7 +1765,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
  * Call me with the zone->lock already held.
  */
 static struct page *__rmqueue(struct zone *zone, unsigned int order,
-						int migratetype)
+				int migratetype, gfp_t gfp_flags)
 {
 	struct page *page;
 
@@ -1700,7 +1795,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
 
 	spin_lock(&zone->lock);
 	for (i = 0; i < count; ++i) {
-		struct page *page = __rmqueue(zone, order, migratetype);
+		struct page *page = __rmqueue(zone, order, migratetype, 0);
 		if (unlikely(page == NULL))
 			break;
 
@@ -2072,7 +2167,7 @@ int split_free_page(struct page *page)
 static inline
 struct page *buffered_rmqueue(struct zone *preferred_zone,
 			struct zone *zone, unsigned int order,
-			gfp_t gfp_flags, int migratetype)
+			gfp_t gfp_flags, int alloc_flags, int migratetype)
 {
 	unsigned long flags;
 	struct page *page;
@@ -2115,7 +2210,15 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
 			WARN_ON_ONCE(order > 1);
 		}
 		spin_lock_irqsave(&zone->lock, flags);
-		page = __rmqueue(zone, order, migratetype);
+
+		page = NULL;
+		if (alloc_flags & ALLOC_HARDER) {
+			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
+			if (page)
+				trace_mm_page_alloc_zone_locked(page, order, migratetype);
+		}
+		if (!page)
+			page = __rmqueue(zone, order, migratetype, gfp_flags);
 		spin_unlock(&zone->lock);
 		if (!page)
 			goto failed;
@@ -2226,15 +2329,24 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
 			unsigned long mark, int classzone_idx, int alloc_flags,
 			long free_pages)
 {
-	/* free_pages may go negative - that's OK */
 	long min = mark;
 	int o;
 	long free_cma = 0;
 
+	/* free_pages may go negative - that's OK */
 	free_pages -= (1 << order) - 1;
+
 	if (alloc_flags & ALLOC_HIGH)
 		min -= min / 2;
-	if (alloc_flags & ALLOC_HARDER)
+
+	/*
+	 * If the caller does not have rights to ALLOC_HARDER then subtract
+	 * the high-atomic reserves. This will over-estimate the size of the
+	 * atomic reserve but it avoids a search.
+	 */
+	if (likely(!(alloc_flags & ALLOC_HARDER)))
+		free_pages -= z->nr_reserved_highatomic;
+	else
 		min -= min / 4;
 
 #ifdef CONFIG_CMA
@@ -2419,10 +2531,18 @@ zonelist_scan:
 
 try_this_zone:
 		page = buffered_rmqueue(ac->preferred_zone, zone, order,
-						gfp_mask, ac->migratetype);
+				gfp_mask, alloc_flags, ac->migratetype);
 		if (page) {
 			if (prep_new_page(page, order, gfp_mask, alloc_flags))
 				goto try_this_zone;
+
+			/*
+			 * If this is a high-order atomic allocation then check
+			 * if the pageblock should be reserved for the future
+			 */
+			if (unlikely(order && (alloc_flags & ALLOC_HARDER)))
+				reserve_highatomic_pageblock(page, zone, order);
+
 			return page;
 		}
 	}
@@ -2695,9 +2815,11 @@ retry:
 
 	/*
 	 * If an allocation failed after direct reclaim, it could be because
-	 * pages are pinned on the per-cpu lists. Drain them and try again
+	 * pages are pinned on the per-cpu lists or in high alloc reserves.
+	 * Shrink them them and try again
 	 */
 	if (!page && !drained) {
+		unreserve_highatomic_pageblock(ac);
 		drain_all_pages(NULL);
 		drained = true;
 		goto retry;