For background, mm/userfaultfd.c provides a general mcopy_atomic implementation. But some types of memory (e.g., hugetlb and shmem) need a slightly different implementation, so they provide their own helpers for this. In other words, userfaultfd is the only caller of this function.
This patch achieves two things: 1. Don't spend time compiling code which will end up never being referenced anyway (a small build time optimization). 2. In future patches (e.g. [1]), we plan to extend the signature of these helpers with UFFD-specific state (e.g., enums or structs defined conditionally in userfaultfd_k.h). Once this happens, this patch will be needed to avoid build errors (or, we'd need to define more UFFD-only stuff unconditionally, which seems messier to me). Peter Xu suggested this be sent as a standalone patch, in the mailing list discussion for [1]. [1] https://patchwork.kernel.org/project/linux-mm/list/?series=424091 Signed-off-by: Axel Rasmussen <axelrasmus...@google.com> --- include/linux/hugetlb.h | 4 ++++ mm/hugetlb.c | 2 ++ 2 files changed, 6 insertions(+) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ebca2ef02212..749701b5c153 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -134,11 +134,13 @@ void hugetlb_show_meminfo(void); unsigned long hugetlb_total_pages(void); vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags); +#ifdef CONFIG_USERFAULTFD int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, pte_t *dst_pte, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, struct page **pagep); +#endif int hugetlb_reserve_pages(struct inode *inode, long from, long to, struct vm_area_struct *vma, vm_flags_t vm_flags); @@ -308,6 +310,7 @@ static inline void hugetlb_free_pgd_range(struct mmu_gather *tlb, BUG(); } +#ifdef CONFIG_USERFAULTFD static inline int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, pte_t *dst_pte, struct vm_area_struct *dst_vma, @@ -318,6 +321,7 @@ static inline int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, BUG(); return 0; } +#endif static inline pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 18f6ee317900..821bfa9c0c80 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4615,6 +4615,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, return ret; } +#ifdef CONFIG_USERFAULTFD /* * Used by userfaultfd UFFDIO_COPY. Based on mcopy_atomic_pte with * modifications for huge pages. @@ -4745,6 +4746,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, put_page(page); goto out; } +#endif long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, -- 2.30.0.365.g02bc693789-goog
