From 6e7a81b5aa1db2f1e35a1859c5107ff57aa51272 Mon Sep 17 00:00:00 2001 From: KOSAKI Motohiro Date: Tue, 5 Nov 2013 16:55:55 +1100 Subject: [PATCH] mm: __rmqueue_fallback() should respect pageblock type When __rmqueue_fallback() doesn't find a free block with the required size it splits a larger page and puts the rest of the page onto the free list. But it has one serious mistake. When putting back, __rmqueue_fallback() always use start_migratetype if type is not CMA. However, __rmqueue_fallback() is only called when all of the start_migratetype queue is empty. That said, __rmqueue_fallback always puts back memory to the wrong queue except try_to_steal_freepages() changed pageblock type (i.e. requested size is smaller than half of page block). The end result is that the antifragmentation framework increases fragmenation instead of decreasing it. Mel's original anti fragmentation does the right thing. But commit 47118af076 ("mm: mmzone: MIGRATE_CMA migration type added") broke it. This patch restores sane and old behavior. And also it remvoe an incorrect comment which introduced at commit fef903efcf (mm/page_alloc.c: restructure free-page stealing code and fix a bug). Signed-off-by: KOSAKI Motohiro Cc: Mel Gorman Cc: Michal Nazarewicz Signed-off-by: Andrew Morton --- mm/page_alloc.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4fb74a8294b0..3dc034f842ab 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1027,6 +1027,10 @@ static int try_to_steal_freepages(struct zone *zone, struct page *page, { int current_order = page_order(page); + /* + * When borrowing from MIGRATE_CMA, we need to release the excess + * buddy pages to CMA itself. + */ if (is_migrate_cma(fallback_type)) return fallback_type; @@ -1091,17 +1095,8 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype) list_del(&page->lru); rmv_page_order(page); - /* - * Borrow the excess buddy pages as well, irrespective - * of whether we stole freepages, or took ownership of - * the pageblock or not. - * - * Exception: When borrowing from MIGRATE_CMA, release - * the excess buddy pages to CMA itself. - */ expand(zone, page, order, current_order, area, - is_migrate_cma(migratetype) - ? migratetype : start_migratetype); + new_type); trace_mm_page_alloc_extfrag(page, order, current_order, start_migratetype, migratetype, new_type); -- 2.39.5