From 5eb5cea11dcbafaa37685bc4e89e1d4ae9c434ea Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Wed, 11 Jan 2023 14:29:02 +0000 Subject: [PATCH] mm: reimplement compound_order() Make compound_order() use struct folio. It can't be turned into a wrapper around folio_order() as a page can be turned into a tail page between a check in compound_order() and the assertion in folio_test_large(). Link: https://lkml.kernel.org/r/20230111142915.1001531-17-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Andrew Morton --- include/linux/mm.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 7ff6e2410aa33..3adc37cebe6f3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -719,11 +719,20 @@ int vma_is_stack_for_current(struct vm_area_struct *vma); struct mmu_gather; struct inode; +/* + * compound_order() can be called without holding a reference, which means + * that niceties like page_folio() don't work. These callers should be + * prepared to handle wild return values. For example, PG_head may be + * set before _folio_order is initialised, or this may be a tail page. + * See compaction.c for some good examples. + */ static inline unsigned int compound_order(struct page *page) { - if (!PageHead(page)) + struct folio *folio = (struct folio *)page; + + if (!test_bit(PG_head, &folio->flags)) return 0; - return page[1].compound_order; + return folio->_folio_order; } /** -- 2.30.2