Re: [PATCH v3 2/5] mm: userfaultfd: don't pass around both mm and vma

Peter Xu
2023-03-07T01:03:33Z

On Mon, Mar 06, 2023 at 02:50:21PM -0800, Axel Rasmussen wrote:
> Quite a few userfaultfd functions took both mm and vma pointers as
> arguments. Since the mm is trivially accessible via vma->vm_mm, there's
> no reason to pass both; it just needlessly extends the already long
> argument list.
>
> Get rid of the mm pointer, where possible, to shorten the argument list.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>

Acked-by: Peter Xu <peterx@redhat.com>

One nit below:

> @@ -6277,7 +6276,7 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
> folio_in_pagecache = true;
> }
>
> - ptl = huge_pte_lock(h, dst_mm, dst_pte);
> + ptl = huge_pte_lock(h, dst_vma->vm_mm, dst_pte);
>
> ret = -EIO;
> if (folio_test_hwpoison(folio))
> @@ -6319,9 +6318,9 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
> if (wp_copy)
> _dst_pte = huge_pte_mkuffd_wp(_dst_pte);
>
> - set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
> + set_huge_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
>
> - hugetlb_count_add(pages_per_huge_page(h), dst_mm);
> + hugetlb_count_add(pages_per_huge_page(h), dst_vma->vm_mm);

When vm_mm referenced multiple times (say, >=3?), let's still cache it in a
temp var?

I'm not sure whether compiler is smart enough to already do that with a
reg, even if so it may slightly improve readability too, imho, by avoiding
the multiple but same indirection for the reader.

Thanks,

--
Peter Xu