[RFC PATCH 08/26] mm: page_alloc: claim blocks during compaction capturing

[Johannes Weiner <hannes@cmpxchg.org>]

When capturing a whole block, update the migratetype accordingly. For
example, a THP allocation might capture an unmovable block. If the THP
gets split and partially freed later, the remainder should group up
with movable allocations.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/internal.h   |  1 +
 mm/page_alloc.c | 42 ++++++++++++++++++++++++------------------
 2 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 024affd4e4b5..39f65a463631 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -432,6 +432,7 @@ struct compact_control {
  */
 struct capture_control {
 	struct compact_control *cc;
+	int migratetype;
 	struct page *page;
 };
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4d20513c83be..8e5996f8b4b4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -615,6 +615,17 @@ void set_pageblock_migratetype(struct page *page, int migratetype)
 				page_to_pfn(page), MIGRATETYPE_MASK);
 }
 
+static void change_pageblock_range(struct page *pageblock_page,
+					int start_order, int migratetype)
+{
+	int nr_pageblocks = 1 << (start_order - pageblock_order);
+
+	while (nr_pageblocks--) {
+		set_pageblock_migratetype(pageblock_page, migratetype);
+		pageblock_page += pageblock_nr_pages;
+	}
+}
+
 #ifdef CONFIG_DEBUG_VM
 static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 {
@@ -962,14 +973,19 @@ compaction_capture(struct capture_control *capc, struct page *page,
 	    is_migrate_isolate(migratetype))
 		return false;
 
-	/*
-	 * Do not let lower order allocations pollute a movable pageblock.
-	 * This might let an unmovable request use a reclaimable pageblock
-	 * and vice-versa but no more than normal fallback logic which can
-	 * have trouble finding a high-order free page.
-	 */
-	if (order < pageblock_order && migratetype == MIGRATE_MOVABLE)
+	if (order >= pageblock_order) {
+		migratetype = capc->migratetype;
+		change_pageblock_range(page, order, migratetype);
+	} else if (migratetype == MIGRATE_MOVABLE) {
+		/*
+		 * Do not let lower order allocations pollute a
+		 * movable pageblock.  This might let an unmovable
+		 * request use a reclaimable pageblock and vice-versa
+		 * but no more than normal fallback logic which can
+		 * have trouble finding a high-order free page.
+		 */
 		return false;
+	}
 
 	capc->page = page;
 	return true;
@@ -2674,17 +2690,6 @@ int move_freepages_block(struct zone *zone, struct page *page,
 			      old_mt, new_mt, num_movable);
 }
 
-static void change_pageblock_range(struct page *pageblock_page,
-					int start_order, int migratetype)
-{
-	int nr_pageblocks = 1 << (start_order - pageblock_order);
-
-	while (nr_pageblocks--) {
-		set_pageblock_migratetype(pageblock_page, migratetype);
-		pageblock_page += pageblock_nr_pages;
-	}
-}
-
 /*
  * When we are falling back to another migratetype during allocation, try to
  * steal extra free pages from the same pageblocks to satisfy further
@@ -4481,6 +4486,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 	unsigned long pflags;
 	unsigned int noreclaim_flag;
 	struct capture_control capc = {
+		.migratetype = ac->migratetype,
 		.page = NULL,
 	};
 
-- 
2.39.2