From 293ffa5ebb9c08a77d8de458166c31b4d7b0cd65 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Thu, 15 Oct 2020 20:09:30 -0700 Subject: mm/page_alloc: move pages to tail in move_to_free_list() Whenever we move pages between freelists via move_to_free_list()/ move_freepages_block(), we don't actually touch the pages: 1. Page isolation doesn't actually touch the pages, it simply isolates pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist. When undoing isolation, we move the pages back to the target list. 2. Page stealing (steal_suitable_fallback()) moves free pages directly between lists without touching them. 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves free pages directly between freelists without touching them. We already place pages to the tail of the freelists when undoing isolation via __putback_isolated_page(), let's do it in any case (e.g., if order <= pageblock_order) and document the behavior. To simplify, let's move the pages to the tail for all move_to_free_list()/move_freepages_block() users. In 2., the target list is empty, so there should be no change. In 3., we might observe a change, however, highatomic is more concerned about allocations succeeding than cache hotness - if we ever realize this change degrades a workload, we can special-case this instance and add a proper comment. This change results in all pages getting onlined via online_pages() to be placed to the tail of the freelist. Signed-off-by: David Hildenbrand Signed-off-by: Andrew Morton Reviewed-by: Oscar Salvador Reviewed-by: Wei Yang Acked-by: Pankaj Gupta Acked-by: Michal Hocko Cc: Alexander Duyck Cc: Mel Gorman Cc: Dave Hansen Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Scott Cheloha Cc: Michael Ellerman Cc: Haiyang Zhang Cc: "K. Y. Srinivasan" Cc: Matthew Wilcox Cc: Michal Hocko Cc: Stephen Hemminger Cc: Wei Liu Link: https://lkml.kernel.org/r/20201005121534.15649-4-david@redhat.com Signed-off-by: Linus Torvalds --- mm/page_isolation.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'mm/page_isolation.c') diff --git a/mm/page_isolation.c b/mm/page_isolation.c index abfe26ad59fd..83692b937784 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -106,6 +106,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) * If we isolate freepage with more than pageblock_order, there * should be no freepage in the range, so we could avoid costly * pageblock scanning for freepage moving. + * + * We didn't actually touch any of the isolated pages, so place them + * to the tail of the freelist. This is an optimization for memory + * onlining - just onlined memory won't immediately be considered for + * allocation. */ if (!isolated_page) { nr_pages = move_freepages_block(zone, page, migratetype, NULL); -- cgit v1.2.3