Re: [PATCH v2 1/3] mm: change huge_ptep_clear_flush() to return the original pte

Muchun Song
2022-05-08T11:09:45Z

On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
> table when unmapping or migrating a hugetlb page, and will change
> to use huge_ptep_clear_flush() instead in the following patches.
>
> So this is a preparation patch, which changes the huge_ptep_clear_flush()
> to return the original pte to help to nuke a hugetlb page table.
>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: Mike Kravetz <mike.kravetz@oracle.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

But one nit below:

[...]
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8605d7e..61a21af 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
> ClearHPageRestoreReserve(new_page);
>
> /* Break COW or unshare */
> - huge_ptep_clear_flush(vma, haddr, ptep);
> + (void)huge_ptep_clear_flush(vma, haddr, ptep);

Why add a "(void)" here? Is there any warning if no "(void)"?
IIUC, I think we can remove this, right?

> mmu_notifier_invalidate_range(mm, range.start, range.end);
> page_remove_rmap(old_page, vma, true);
> hugepage_add_new_anon_rmap(new_page, vma, haddr);
> --
> 1.8.3.1
>
>