Re: [PATCH 2/5] mm/page_alloc: Add a bulk page allocator

Signed-off-by: Mel Gorman <redacted>

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 4a304fd39916..fb6234e1fe59 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h

@@ -520,13 +520,20 @@ struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid,
 
 int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 				nodemask_t *nodemask, int nr_pages,
-				struct list_head *list);
+				struct list_head *page_list,
+				struct page **page_array);
 
 /* Bulk allocate order-0 pages */
 static inline unsigned long
-alloc_pages_bulk(gfp_t gfp, unsigned long nr_pages, struct list_head *list)
+alloc_pages_bulk_list(gfp_t gfp, unsigned long nr_pages, struct list_head *list)
 {
-	return __alloc_pages_bulk(gfp, numa_mem_id(), NULL, nr_pages, list);
+	return __alloc_pages_bulk(gfp, numa_mem_id(), NULL, nr_pages, list, NULL);
+}
+
+static inline unsigned long
+alloc_pages_bulk_array(gfp_t gfp, unsigned long nr_pages, struct page **page_array)
+{
+	return __alloc_pages_bulk(gfp, numa_mem_id(), NULL, nr_pages, NULL, page_array);
 }
 
 /*

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3e0c87c588d3..96590f0726c7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -4965,13 +4965,20 @@ static inline bool prepare_alloc_pages(gfp_t gfp, unsigned int order,
 
 /*
  * This is a batched version of the page allocator that attempts to
- * allocate nr_pages quickly from the preferred zone and add them to list.
+ * allocate nr_pages quickly from the preferred zone. Pages are added
+ * to page_list if page_list is not NULL, otherwise it is assumed
+ * that the page_array is valid.
+ *
+ * If using page_array, only NULL elements are populated with pages.
+ * The caller must ensure that the array has enough NULL elements
+ * to store nr_pages or the buffer overruns.
  *
  * Returns the number of pages allocated.
  */
 int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 			nodemask_t *nodemask, int nr_pages,
-			struct list_head *alloc_list)
+			struct list_head *page_list,
+			struct page **page_array)
 {
 	struct page *page;
 	unsigned long flags;

@@ -4987,6 +4994,9 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 	if (WARN_ON_ONCE(nr_pages <= 0))
 		return 0;
 
+	if (WARN_ON_ONCE(!page_list && !page_array))
+		return 0;
+
 	if (nr_pages == 1)
 		goto failed;
 

@@ -5035,7 +5045,24 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 			break;
 		}
 
-		list_add(&page->lru, alloc_list);
+		if (page_list) {
+			/* New page prep is deferred */
+			list_add(&page->lru, page_list);
+		} else {
+			/* Skip populated elements */
+			while (*page_array)
+				page_array++;

+
+			/*
+			 * Array pages must be prepped immediately to
+			 * avoid tracking which pages are new and
+			 * which ones were already on the array.
+			 */
+			prep_new_page(page, 0, gfp, 0);
+			*page_array = page;
+			page_array++;
+		}
+
 		allocated++;
 	}
 

@@ -5044,9 +5071,12 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 
 	local_irq_restore(flags);
 
-	/* Prep page with IRQs enabled to reduce disabled times */
-	list_for_each_entry(page, alloc_list, lru)
-		prep_new_page(page, 0, gfp, 0);
+	/* Prep pages with IRQs enabled if using a list */
+	if (page_list) {
+		list_for_each_entry(page, page_list, lru) {
+			prep_new_page(page, 0, gfp, 0);
+		}
+	}
 
 	return allocated;
 

@@ -5056,7 +5086,10 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 failed:
 	page = __alloc_pages(gfp, 0, preferred_nid, nodemask);
 	if (page) {
-		list_add(&page->lru, alloc_list);
+		if (page_list)
+			list_add(&page->lru, page_list);
+		else
+			*page_array = page;
 		allocated = 1;
 	}