From: Muchun Song songmuchun@bytedance.com
commit 7ad69832f37e3cea8557db6df7c793905f1135e8 upstream.
When we free a page whose order is very close to MAX_ORDER and greater than pageblock_order, it wastes some CPU cycles to increase max_order to MAX_ORDER one by one and check the pageblock migratetype of that page repeatedly especially when MAX_ORDER is much larger than pageblock_order.
We also should not be checking migratetype of buddy when "order == MAX_ORDER - 1" as the buddy pfn may be invalid, so adjust the condition. With the new check, we don't need the max_order check anymore, so we replace it.
Also adjust max_order initialization so that it's lower by one than previously, which makes the code hopefully more clear.
Link: https://lkml.kernel.org/r/20201204155109.55451-1-songmuchun@bytedance.com Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks") Signed-off-by: Muchun Song songmuchun@bytedance.com Acked-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: Oscar Salvador osalvador@suse.de Reviewed-by: David Hildenbrand david@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/page_alloc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -814,7 +814,7 @@ static inline void __free_one_page(struc struct page *buddy; unsigned int max_order;
- max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1); + max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order);
VM_BUG_ON(!zone_is_initialized(zone)); VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page); @@ -829,7 +829,7 @@ static inline void __free_one_page(struc VM_BUG_ON_PAGE(bad_range(zone, page), page);
continue_merging: - while (order < max_order - 1) { + while (order < max_order) { buddy_idx = __find_buddy_index(page_idx, order); buddy = page + (buddy_idx - page_idx); if (!page_is_buddy(page, buddy, order)) @@ -850,7 +850,7 @@ continue_merging: page_idx = combined_idx; order++; } - if (max_order < MAX_ORDER) { + if (order < MAX_ORDER - 1) { /* If we are here, it means order is >= pageblock_order. * We want to prevent merge between freepages on isolate * pageblock and normal pageblock. Without this, pageblock @@ -871,7 +871,7 @@ continue_merging: is_migrate_isolate(buddy_mt))) goto done_merging; } - max_order++; + max_order = order + 1; goto continue_merging; }