Re: [PATCH v5 5/6] mm: convert copy_user_huge_page() to copy_user_folio()

Mike Kravetz
2023-04-06T23:56:19Z

On 03/31/23 17:39, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
>
> Replace copy_user_huge_page() with copy_user_folio(). copy_user_folio()
> does the same as copy_user_huge_page(), but takes in folios instead of
> pages. Convert copy_user_gigantic_page() to take in folios.
> Remove pages_per_huge_page from copy_user_folio(), because we can get
> that from folio_nr_pages(dst).
>
> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
> ---
> include/linux/mm.h | 7 +++----
> mm/hugetlb.c | 10 ++++------
> mm/memory.c | 28 ++++++++++++++--------------
> 3 files changed, 21 insertions(+), 24 deletions(-)

No technical problems with the patch, but ...
>
> @@ -5847,15 +5847,15 @@ static void copy_subpage(unsigned long addr, int idx, void *arg)
> addr, copy_arg->vma);
> }
>
> -void copy_user_huge_page(struct page *dst, struct page *src,
> - unsigned long addr_hint, struct vm_area_struct *vma,
> - unsigned int pages_per_huge_page)
> +void copy_user_folio(struct folio *dst, struct folio *src,
> + unsigned long addr_hint, struct vm_area_struct *vma)
> {
> + unsigned int pages_per_huge_page = folio_nr_pages(dst);
> unsigned long addr = addr_hint &
> ~(((unsigned long)pages_per_huge_page << PAGE_SHIFT) - 1);
> struct copy_subpage_arg arg = {
> - .dst = dst,
> - .src = src,
> + .dst = &dst->page,
> + .src = &src->page,
> .vma = vma,
> };
>

I seem to recall that Matthew suggested changing the function name to
copy_user_folio. My only concern is that the name now sounds like a
general purpose routine for copying folios. It certainly would work
for a single page folio, but there is a bunch of unnecessary overhead
in that case.

That makes me think there should perhaps be an optimized path for single
page folios that just does copy_user_highpage(). But, the argument addr_hint
does not make much sense in the single page folio case. So, I am not
sure if I agree with leaving large/huge out of the function name.

Just wondering if Matthew has any additional thoughts?
--
Mike Kravetz