linux-kernel - Re: [RFC PATCH 01/26] hugetlb: make hstate accessor functions const

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Date:   Tue, 28 Jun 2022 10:08:18 -0700
From:   James Houghton <jthoughton@...gle.com>
To:     "manish.mishra" <manish.mishra@...anix.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Jue Wang <juew@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 01/26] hugetlb: make hstate accessor functions const

On Mon, Jun 27, 2022 at 5:09 AM manish.mishra <manish.mishra@...anix.com> wrote:
>
>
> On 27/06/22 5:06 pm, manish.mishra wrote:
>
>
> On 24/06/22 11:06 pm, James Houghton wrote:
>
> This is just a const-correctness change so that the new hugetlb_pte
> changes can be const-correct too.
>
> Acked-by: David Rientjes <rientjes@...gle.com>
>
> Signed-off-by: James Houghton <jthoughton@...gle.com>
> ---
>  include/linux/hugetlb.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index e4cff27d1198..498a4ae3d462 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -715,7 +715,7 @@ static inline struct hstate *hstate_vma(struct vm_area_struct *vma)
>   return hstate_file(vma->vm_file);
>  }
>
> -static inline unsigned long huge_page_size(struct hstate *h)
> +static inline unsigned long huge_page_size(const struct hstate *h)
>  {
>   return (unsigned long)PAGE_SIZE << h->order;
>  }
> @@ -729,27 +729,27 @@ static inline unsigned long huge_page_mask(struct hstate *h)
>   return h->mask;
>  }
>
> -static inline unsigned int huge_page_order(struct hstate *h)
> +static inline unsigned int huge_page_order(const struct hstate *h)
>  {
>   return h->order;
>  }
>
> -static inline unsigned huge_page_shift(struct hstate *h)
> +static inline unsigned huge_page_shift(const struct hstate *h)
>  {
>   return h->order + PAGE_SHIFT;
>  }
>
> -static inline bool hstate_is_gigantic(struct hstate *h)
> +static inline bool hstate_is_gigantic(const struct hstate *h)
>  {
>   return huge_page_order(h) >= MAX_ORDER;
>  }
>
> -static inline unsigned int pages_per_huge_page(struct hstate *h)
> +static inline unsigned int pages_per_huge_page(const struct hstate *h)
>  {
>   return 1 << h->order;
>  }
>
> -static inline unsigned int blocks_per_huge_page(struct hstate *h)
> +static inline unsigned int blocks_per_huge_page(const struct hstate *h)
>  {
>   return huge_page_size(h) / 512;
>  }
>
> James, Just wanted to check why you did it selectively only for these functions
>
> why not for something like hstate_index which too i see used in your code.

I'll look into which other functions can be made const. We need
huge_page_shift() to take `const struct hstate *h` so that the hstates
can be sorted, and it then followed to make the surrounding, related
functions const as well. I could also just leave it at
huge_page_shift().

The commit message here is wrong -- the hugetlb_pte const-correctness
is a separate issue that doesn't depend the constness of hstates. I'll
fix that -- sorry about that.