From 97a7e4733b9b221d012ae68fcd3b3251febf6341 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Fri, 12 Mar 2021 21:07:26 -0800 Subject: mm: introduce page_needs_cow_for_dma() for deciding whether cow We've got quite a few places (pte, pmd, pud) that explicitly checked against whether we should break the cow right now during fork(). It's easier to provide a helper, especially before we work the same thing on hugetlbfs. Since we'll reference is_cow_mapping() in mm.h, move it there too. Actually it suites mm.h more since internal.h is mm/ only, but mm.h is exported to the whole kernel. With that we should expect another patch to use is_cow_mapping() whenever we can across the kernel since we do use it quite a lot but it's always done with raw code against VM_* flags. Link: https://lkml.kernel.org/r/20210217233547.93892-4-peterx@redhat.com Signed-off-by: Peter Xu Reviewed-by: Jason Gunthorpe Cc: Alexey Dobriyan Cc: Andrea Arcangeli Cc: Christoph Hellwig Cc: Daniel Vetter Cc: David Airlie Cc: David Gibson Cc: Gal Pressman Cc: Jan Kara Cc: Jann Horn Cc: Kirill Shutemov Cc: Kirill Tkhai Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Mike Kravetz Cc: Mike Rapoport Cc: Roland Scheidegger Cc: VMware Graphics Cc: Wei Zhang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index c8e357627318..523230005db1 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -809,12 +809,8 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss, struct page **prealloc, pte_t pte, struct page *page) { - struct mm_struct *src_mm = src_vma->vm_mm; struct page *new_page; - if (!is_cow_mapping(src_vma->vm_flags)) - return 1; - /* * What we want to do is to check whether this page may * have been pinned by the parent process. If so, @@ -828,9 +824,7 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma * the page count. That might give false positives for * for pinning, but it will work correctly. */ - if (likely(!atomic_read(&src_mm->has_pinned))) - return 1; - if (likely(!page_maybe_dma_pinned(page))) + if (likely(!page_needs_cow_for_dma(src_vma, page))) return 1; new_page = *prealloc; -- cgit