[RFC PATCH 5/5] mm/page_alloc: claim blocks captured for non-movable use

[Rik van Riel <riel@surriel.com>]

compaction_capture() hands any merged block to the compacting task
with no type change, except it refuses a movable block to a
non-movable request below pageblock order. A non-movable request
capturing a whole movable block leaves non-movable content in a
movable-typed block.

Make a non-movable capture claim a movable block: convert it to
the request. A partial block cannot be retyped, so the refusal
below pageblock order stays; reaching the conversion means a
whole block. A movable capture steals: it takes the pages and
leaves the type alone.

Assisted-by: LLM
Signed-off-by: Rik van Riel <riel@surriel.com>
---
 mm/page_alloc.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 16d3594d913a0..edb69d8a74c73 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -728,6 +728,9 @@ static inline struct capture_control *task_capc(struct zone *zone)
 		capc->zone == zone ? capc : NULL;
 }
 
+static void change_pageblock_range(struct page *pageblock_page,
+				   int start_order, int migratetype);
+
 static inline bool
 compaction_capture(struct capture_control *capc, struct page *page,
 		   int order, int migratetype)
@@ -751,6 +754,19 @@ compaction_capture(struct capture_control *capc, struct page *page,
 	    capc->migratetype != MIGRATE_MOVABLE)
 		return false;
 
+	/*
+	 * A non-movable capture claims a movable block: convert it to
+	 * the request. A movable capture steals: take the pages and
+	 * leave the type alone. Partial movable blocks returned above,
+	 * so reaching here means a whole block.
+	 */
+	if (capc->migratetype != MIGRATE_MOVABLE &&
+	    migratetype == MIGRATE_MOVABLE) {
+		change_pageblock_range(page, order, capc->migratetype);
+		/* Converted whole, so no fragmentation to report below. */
+		migratetype = capc->migratetype;
+	}
+
 	if (migratetype != capc->migratetype)
 		trace_mm_page_alloc_extfrag(page, capc->order, order,
 					    capc->migratetype, migratetype);
-- 
2.53.0-Meta