linux-kernel - Re: [RFC PATCH 08/26] hugetlb: add hugetlb_free

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Date:   Tue, 28 Jun 2022 13:27:44 -0700
From:   Mina Almasry <almasrymina@...gle.com>
To:     James Houghton <jthoughton@...gle.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>,
        Jue Wang <juew@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 08/26] hugetlb: add hugetlb_free_range to free PT structures

On Fri, Jun 24, 2022 at 10:37 AM James Houghton <jthoughton@...gle.com> wrote:
>
> This is a helper function for freeing the bits of the page table that
> map a particular HugeTLB PTE.
>
> Signed-off-by: James Houghton <jthoughton@...gle.com>
> ---
>  include/linux/hugetlb.h |  2 ++
>  mm/hugetlb.c            | 17 +++++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 1d4ec9dfdebf..33ba48fac551 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -107,6 +107,8 @@ bool hugetlb_pte_none_mostly(const struct hugetlb_pte *hpte);
>  pte_t hugetlb_ptep_get(const struct hugetlb_pte *hpte);
>  void hugetlb_pte_clear(struct mm_struct *mm, const struct hugetlb_pte *hpte,
>                        unsigned long address);
> +void hugetlb_free_range(struct mmu_gather *tlb, const struct hugetlb_pte *hpte,
> +                       unsigned long start, unsigned long end);
>
>  struct hugepage_subpool {
>         spinlock_t lock;
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1a1434e29740..a2d2ffa76173 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1120,6 +1120,23 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg)
>         return false;
>  }
>
> +void hugetlb_free_range(struct mmu_gather *tlb, const struct hugetlb_pte *hpte,
> +                       unsigned long start, unsigned long end)
> +{
> +       unsigned long floor = start & hugetlb_pte_mask(hpte);
> +       unsigned long ceiling = floor + hugetlb_pte_size(hpte);
> +
> +       if (hugetlb_pte_size(hpte) >= PGDIR_SIZE) {
> +               free_p4d_range(tlb, (pgd_t *)hpte->ptep, start, end, floor, ceiling);
> +       } else if (hugetlb_pte_size(hpte) >= P4D_SIZE) {
> +               free_pud_range(tlb, (p4d_t *)hpte->ptep, start, end, floor, ceiling);
> +       } else if (hugetlb_pte_size(hpte) >= PUD_SIZE) {
> +               free_pmd_range(tlb, (pud_t *)hpte->ptep, start, end, floor, ceiling);
> +       } else if (hugetlb_pte_size(hpte) >= PMD_SIZE) {
> +               free_pte_range(tlb, (pmd_t *)hpte->ptep, start);
> +       }

Same as the previous patch: I wonder about >=, and if possible
calculate hugetlb_pte_size() once, or use *_SHIFT comparison.

> +}
> +
>  bool hugetlb_pte_present_leaf(const struct hugetlb_pte *hpte)
>  {
>         pgd_t pgd;
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>