[PATCH] mm: page_alloc: simpify page del and expand

[Huan Yang <link@xxxxxxxx>]

When page del from buddy and need expand, it will account free_pages
in zone's migratetype.

The current way is to subtract the page number of the current order
when deleting, and then add it back when expanding.

This is unnecessary, as when migrating the same type, we can directly
record the difference between the high-order pages and the expand
added, and then subtract it directly.

This patch merge that, only when del and expand done, then account
free_pages.

Signed-off-by: Huan Yang <link@xxxxxxxx>
---
 mm/page_alloc.c | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 023132f66d29..900b0947c6e1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1363,11 +1363,11 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
  *
  * -- nyc
  */
-static inline void expand(struct zone *zone, struct page *page,
-	int low, int high, int migratetype)
+static inline unsigned int expand(struct zone *zone, struct page *page, int low,
+				  int high, int migratetype)
 {
-	unsigned long size = 1 << high;
-	unsigned long nr_added = 0;
+	unsigned int size = 1 << high;
+	unsigned int nr_added = 0;
 
 	while (high > low) {
 		high--;
@@ -1387,7 +1387,19 @@ static inline void expand(struct zone *zone, struct page *page,
 		set_buddy_order(&page[size], high);
 		nr_added += size;
 	}
-	account_freepages(zone, nr_added, migratetype);
+
+	return nr_added;
+}
+
+static __always_inline void page_del_and_expand(struct zone *zone,
+						struct page *page, int low,
+						int high, int migratetype)
+{
+	int nr_pages = 1 << high;
+
+	__del_page_from_free_list(page, zone, high, migratetype);
+	nr_pages -= expand(zone, page, low, high, migratetype);
+	account_freepages(zone, -nr_pages, migratetype);
 }
 
 static void check_new_page_bad(struct page *page)
@@ -1557,8 +1569,9 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 		page = get_page_from_free_area(area, migratetype);
 		if (!page)
 			continue;
-		del_page_from_free_list(page, zone, current_order, migratetype);
-		expand(zone, page, order, current_order, migratetype);
+
+		page_del_and_expand(zone, page, order, current_order,
+				    migratetype);
 		trace_mm_page_alloc_zone_locked(page, order, migratetype,
 				pcp_allowed_order(order) &&
 				migratetype < MIGRATE_PCPTYPES);
@@ -1888,9 +1901,12 @@ steal_suitable_fallback(struct zone *zone, struct page *page,
 
 	/* Take ownership for orders >= pageblock_order */
 	if (current_order >= pageblock_order) {
+		unsigned int nr_added;
+
 		del_page_from_free_list(page, zone, current_order, block_type);
 		change_pageblock_range(page, current_order, start_type);
-		expand(zone, page, order, current_order, start_type);
+		nr_added = expand(zone, page, order, current_order, start_type);
+		account_freepages(zone, nr_added, start_type);
 		return page;
 	}
 
@@ -1943,8 +1959,7 @@ steal_suitable_fallback(struct zone *zone, struct page *page,
 	}
 
 single_page:
-	del_page_from_free_list(page, zone, current_order, block_type);
-	expand(zone, page, order, current_order, block_type);
+	page_del_and_expand(zone, page, order, current_order, block_type);
 	return page;
 }
 
-- 
2.45.2