From: Wei Yang Date: Fri, 5 Sep 2025 14:03:58 +0000 (+0000) Subject: mm/page_alloc: check the correct buddy if it is a starting block X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=db8e0ce12c8f063bf35ee571503d20bded026656;p=users%2Fjedix%2Flinux-maple.git mm/page_alloc: check the correct buddy if it is a starting block find_large_buddy() search buddy based on start_pfn, which maybe different from page's pfn, e.g. when page is not pageblock aligned, because prep_move_freepages_block() always align start_pfn to pageblock. This means when we found a starting block at start_pfn, it may check on the wrong page theoretically. And not split the free page as it is supposed to, causing a freelist migratetype mismatch. The good news is the page passed to __move_freepages_block_isolate() has only two possible cases: * page is pageblock aligned * page is __first_valid_page() of this block So it is safe for the first case, and it won't get a buddy larger than pageblock for the second case. To fix the issue, check the returned pfn of find_large_buddy() to decide whether to split the free page: 1. if it is not a PageBuddy pfn, no split; 2. if it is a PageBuddy pfn but order <= pageblock_order, no split; 3. if it is a PageBuddy pfn with order > pageblock_order, start_pfn is either in the starting block or tail block, split the PageBuddy at pageblock_order level. Link: https://lkml.kernel.org/r/20250905140358.28849-1-richard.weiyang@gmail.com Signed-off-by: Wei Yang Reviewed-by: Zi Yan Cc: Johannes Weiner Cc: David Hildenbrand Cc: Baolin Wang Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 8de5fb5528eb..df6df302d0c5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2090,9 +2090,10 @@ static inline void toggle_pageblock_isolate(struct page *page, bool isolate) static bool __move_freepages_block_isolate(struct zone *zone, struct page *page, bool isolate) { - unsigned long start_pfn, pfn; + unsigned long start_pfn, buddy_pfn; int from_mt; int to_mt; + struct page *buddy; if (isolate == get_pageblock_isolate(page)) { VM_WARN_ONCE(1, "%s a pageblock that is already in that state", @@ -2107,29 +2108,19 @@ static bool __move_freepages_block_isolate(struct zone *zone, if (pageblock_order == MAX_PAGE_ORDER) goto move; - /* We're a tail block in a larger buddy */ - pfn = find_large_buddy(start_pfn); - if (pfn != start_pfn) { - struct page *buddy = pfn_to_page(pfn); + buddy_pfn = find_large_buddy(start_pfn); + buddy = pfn_to_page(buddy_pfn); + /* We're a part of a larger buddy */ + if (PageBuddy(buddy) && buddy_order(buddy) > pageblock_order) { int order = buddy_order(buddy); del_page_from_free_list(buddy, zone, order, - get_pfnblock_migratetype(buddy, pfn)); + get_pfnblock_migratetype(buddy, buddy_pfn)); toggle_pageblock_isolate(page, isolate); - split_large_buddy(zone, buddy, pfn, order, FPI_NONE); + split_large_buddy(zone, buddy, buddy_pfn, order, FPI_NONE); return true; } - /* We're the starting block of a larger buddy */ - if (PageBuddy(page) && buddy_order(page) > pageblock_order) { - int order = buddy_order(page); - - del_page_from_free_list(page, zone, order, - get_pfnblock_migratetype(page, pfn)); - toggle_pageblock_isolate(page, isolate); - split_large_buddy(zone, page, pfn, order, FPI_NONE); - return true; - } move: /* Use MIGRATETYPE_MASK to get non-isolate migratetype */ if (isolate) {