On Thu, Jan 26, 2012 at 10:00:50AM +0100, Marek Szyprowski wrote:

quoted

From: Michal Nazarewicz <redacted>

@@ -875,10 +895,15 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
  * This array describes the order lists are fallen back to when
  * the free lists for the desirable migrate type are depleted
  */
-static int fallbacks[MIGRATE_TYPES][3] = {
+static int fallbacks[MIGRATE_TYPES][4] = {
 	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_RESERVE },
 	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_RESERVE },
+#ifdef CONFIG_CMA
+	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_CMA    , MIGRATE_RESERVE },

On Mon, 30 Jan 2012 13:35:42 +0100, Mel Gorman [off-list ref] wrote:

This is a curious choice. MIGRATE_CMA is allowed to contain movable
pages. By using MIGRATE_RECLAIMABLE and MIGRATE_UNMOVABLE for movable
pages instead of MIGRATE_CMA, you increase the changes that unmovable
pages will need to use MIGRATE_MOVABLE in the future which impacts
fragmentation avoidance. I would recommend that you change this to

{ MIGRATE_CMA, MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE }

At the beginning the idea was to try hard not to get pages from MIGRATE_CMA
allocated at all, thus it was put at the end of the fallbacks list, but on
a busy system this probably won't help anyway, so I'll change it per your
suggestion.

quoted

@@ -1017,11 +1049,14 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
 			rmv_page_order(page);

 			/* Take ownership for orders >= pageblock_order */
-			if (current_order >= pageblock_order)
+			if (current_order >= pageblock_order &&
+			    !is_pageblock_cma(page))
 				change_pageblock_range(page, current_order,
 							start_migratetype);

-			expand(zone, page, order, current_order, area, migratetype);
+			expand(zone, page, order, current_order, area,
+			       is_migrate_cma(start_migratetype)
+			     ? start_migratetype : migratetype);

What is this check meant to be doing?

start_migratetype is determined by allocflags_to_migratetype() and
that never will be MIGRATE_CMA so is_migrate_cma(start_migratetype)
should always be false.

Right, thanks!  This should be the other way around, ie.:

+			expand(zone, page, order, current_order, area,
+			       is_migrate_cma(migratetype)
+			     ? migratetype : start_migratetype);

I'll fix this and the calls to is_pageblock_cma().

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Micha? ?mina86? Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--