Re: [RFC PATCH v4 7/8] hugetlb: create hugetlb_unmap_file_folio to unmap single file folio

Miaohe Lin
2022-07-29T02:02:56Z

On 2022/7/7 4:23, Mike Kravetz wrote:
> Create the new routine hugetlb_unmap_file_folio that will unmap a single
> file folio. This is refactored code from hugetlb_vmdelete_list. It is
> modified to do locking within the routine itself and check whether the
> page is mapped within a specific vma before unmapping.
>
> This refactoring will be put to use and expanded upon in a subsequent
> patch adding vma specific locking.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> fs/hugetlbfs/inode.c | 124 +++++++++++++++++++++++++++++++++----------
> 1 file changed, 95 insertions(+), 29 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 31bd4325fce5..0eac0ea2a245 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -396,6 +396,94 @@ static int hugetlbfs_write_end(struct file *file, struct address_space *mapping,
> return -EINVAL;
> }
>
> +/*
> + * Called with i_mmap_rwsem held for inode based vma maps. This makes
> + * sure vma (and vm_mm) will not go away. We also hold the hugetlb fault
> + * mutex for the page in the mapping. So, we can not race with page being
> + * faulted into the vma.
> + */
> +static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
> + unsigned long addr, struct page *page)
> +{
> + pte_t *ptep, pte;
> +
> + ptep = huge_pte_offset(vma->vm_mm, addr,
> + huge_page_size(hstate_vma(vma)));
> +
> + if (!ptep)
> + return false;
> +
> + pte = huge_ptep_get(ptep);
> + if (huge_pte_none(pte) || !pte_present(pte))
> + return false;
> +
> + if (pte_page(pte) == page)
> + return true;
> +
> + return false; /* WTH??? */

I'm sorry but what does WTH means? IIUC, this could happen if pte_page is a COW-ed private page?
vma_interval_tree_foreach doesn't exclude the private mapping even after cow?

Except from above (trivial one), this patch looks good to me.

Thanks.