From bcd51a3c679d179cf526414f859c57d081fd37e7 Mon Sep 17 00:00:00 2001 From: Mike Kravetz Date: Tue, 21 Jun 2022 16:56:20 -0700 Subject: [PATCH] hugetlb: lazy page table copies in fork() Lazy page table copying at fork time was introduced with commit d992895ba2b2 ("[PATCH] Lazy page table copies in fork()"). At the time, hugetlb was very new and did not support page faulting. As a result, it was excluded. When full page fault support was added for hugetlb, the exclusion was not removed. Simply remove the check that prevents lazy copying of hugetlb page tables at fork. Of course, like other mappings this only applies to shared mappings. Lazy page table copying at fork will be less advantageous for hugetlb mappings because: - There are fewer page table entries with hugetlb - hugetlb pmds can be shared instead of copied In any case, completely eliminating the copy at fork time should speed things up. Link: https://lkml.kernel.org/r/20220621235620.291305-5-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz Acked-by: Muchun Song Acked-by: David Hildenbrand Cc: "Aneesh Kumar K.V" Cc: Anshuman Khandual Cc: Baolin Wang Cc: Catalin Marinas Cc: Christian Borntraeger Cc: James Houghton Cc: kernel test robot Cc: Michal Hocko Cc: Mina Almasry Cc: Naoya Horiguchi Cc: Paul Walmsley Cc: Peter Xu Cc: Rolf Eike Beer Cc: Will Deacon Signed-off-by: Andrew Morton --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 2392d5db473a..7cd0d4c086db 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1253,7 +1253,7 @@ vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) if (userfaultfd_wp(dst_vma)) return true; - if (src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) + if (src_vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) return true; if (src_vma->anon_vma) -- 2.34.1