Commit 6dda9d55 ( page allocator: reduce fragmentation in buddy allocator by adding buddies that are merging to the tail of the free lists) classified pages according to their probability of being part of a high order merge. This made sense when the number of pages being freed was relatively small as part of a per-cpu list drain.
However, with the introduction of magazines, a drain of the magazines frees larger number of pages in batch and the heuristic is less likely to benefit but adds a lot of weight to the free path in the normal case. The free path can be very hot for workloads with short-lived processes, are fault intensive or work with many in-kernel short-lived buffers. As THP is the main benefit of such a heuristic, it's too marginal a gain to impact the free path so heavily, remove it. Signed-off-by: Mel Gorman <[email protected]> --- mm/page_alloc.c | 22 ---------------------- 1 file changed, 22 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b30abe8..6760e00 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -577,29 +577,7 @@ static inline void __free_one_page(struct page *page, } set_page_order(page, order); - /* - * If this is not the largest possible page, check if the buddy - * of the next-highest order is free. If it is, it's possible - * that pages are being freed that will coalesce soon. In case, - * that is happening, add the free page to the tail of the list - * so it's less likely to be used soon and more likely to be merged - * as a higher order page - */ - if ((order < MAX_ORDER-2) && pfn_valid_within(page_to_pfn(buddy))) { - struct page *higher_page, *higher_buddy; - combined_idx = buddy_idx & page_idx; - higher_page = page + (combined_idx - page_idx); - buddy_idx = __find_buddy_index(combined_idx, order + 1); - higher_buddy = higher_page + (buddy_idx - combined_idx); - if (page_is_buddy(higher_page, higher_buddy, order + 1)) { - list_add_tail(&page->lru, - &zone->free_area[order].free_list[migratetype]); - goto out; - } - } - list_add(&page->lru, &zone->free_area[order].free_list[migratetype]); -out: zone->free_area[order].nr_free++; } -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
