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a/include/linux/hugetlb.h~mm-userfaultfd-fix-hugetlb-fault-mutex-hash-calculation >> +++ a/include/linux/hugetlb.h >> @@ -796,6 +796,23 @@ static inline unsigned huge_page_shift(s >> return h->order + PAGE_SHIFT; >> } >> >> +/** >> + * hugetlb_linear_page_index() - linear_page_index() but in hugetlb >> + * page size granularity. >> + * @vma: the hugetlb VMA >> + * @address: the virtual address within the VMA >> + * >> + * Return: the page offset within the mapping in huge page units. >> + */ >> +static inline pgoff_t hugetlb_linear_page_index(struct vm_area_struct *vma, >> + unsigned long address) >> +{ >> + struct hstate *h = hstate_vma(vma); >> + >> + return ((address - vma->vm_start) >> huge_page_shift(h)) + >> + (vma->vm_pgoff >> huge_page_order(h)); >> +} >> + >> static inline bool order_is_gigantic(unsigned int order) >> { >> return order > MAX_PAGE_ORDER; >> --- a/mm/userfaultfd.c~mm-userfaultfd-fix-hugetlb-fault-mutex-hash-calculation >> +++ a/mm/userfaultfd.c >> @@ -573,7 +573,7 @@ retry: >> * in the case of shared pmds. fault mutex prevents >> * races with other faulting threads. >> */ >> - idx = linear_page_index(dst_vma, dst_addr); >> + idx = hugetlb_linear_page_index(dst_vma, dst_addr); >> mapping = dst_vma->vm_file->f_mapping; >> hash = hugetlb_fault_mutex_hash(mapping, idx); >> mutex_lock(&hugetlb_fault_mutex_table[hash]); >> _ >> > > Let's take a look at other hugetlb_fault_mutex_hash() users: > > * remove_inode_hugepages: uses folio->index >> huge_page_order(h) > -> hugetlb granularity > * hugetlbfs_fallocate(): start/index is in hugetlb granularity > -> hugetlb granularity > * memfd_alloc_folio(): idx >>= huge_page_order(h); > -> hugetlb granularity > * hugetlb_wp(): uses vma_hugecache_offset() > -> hugetlb granularity > * hugetlb_handle_userfault(): uses vmf->pgoff, which hugetlb_fault() > sets to vma_hugecache_offset() > -> hugetlb granularity > * hugetlb_no_page(): similarly uses vmf->pgoff > -> hugetlb granularity > * hugetlb_fault(): similarly uses vmf->pgoff > -> hugetlb granularity > > So this change here looks good to me > > Reviewed-by: David Hildenbrand (Arm) > > > But it raises the question: > > (1) should be convert all that to just operate on the ordinary index, > such that we don't even need hugetlb_linear_page_index()? That would be > an addon patch. > Do you mean to convert all callers of hugetlb_linear_page_index() and vma_hugepcache_offset() to use index and huge_page_order(h) ? May I add, to improve readability, rename the huge-page-granularity 'idx' to huge_idx or hidx ? > (2) Alternatively, could we replace all users of vma_hugecache_offset() > by the much cleaner hugetlb_linear_page_index() ? > The difference between the two helpers is hstate_vma() in the latter that is about 5 pointer de-references, not sure of any performance implication though. At minimum, we could have hugetlb_linear_page_index(vma, addr) -> __hugetlb_linear_page_index(h, vma, addr) basically renaming vma_hugecache_offset(). > In general, I think we should look into having idx/vmf->pgoff being > consistent with the remainder of MM, converting all code in hugetlb to > do that. > > Any takers? > I'd be happy to, just to make sure I understand the proposal clearly. thanks! -jane