linux-kernel - Re: [RFC PATCH 09/26] hugetlb: add hugetlb_hgm

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Date:   Tue, 28 Jun 2022 13:33:19 -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 09/26] hugetlb: add hugetlb_hgm_enabled

On Fri, Jun 24, 2022 at 10:37 AM James Houghton <jthoughton@...gle.com> wrote:
>
> Currently, this is always true if the VMA is shared. In the future, it's
> possible that private mappings will get some or all HGM functionality.
>
> Signed-off-by: James Houghton <jthoughton@...gle.com>

Reviewed-by: Mina Almasry <almasrymina@...gle.com>

> ---
>  include/linux/hugetlb.h | 10 ++++++++++
>  mm/hugetlb.c            |  8 ++++++++
>  2 files changed, 18 insertions(+)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 33ba48fac551..e7a6b944d0cc 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -1174,6 +1174,16 @@ static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
>  }
>  #endif /* CONFIG_HUGETLB_PAGE */
>
> +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> +/* If HugeTLB high-granularity mappings are enabled for this VMA. */
> +bool hugetlb_hgm_enabled(struct vm_area_struct *vma);
> +#else
> +static inline bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
> +{
> +       return false;
> +}
> +#endif
> +
>  static inline spinlock_t *huge_pte_lock(struct hstate *h,
>                                         struct mm_struct *mm, pte_t *pte)
>  {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a2d2ffa76173..8b10b941458d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6983,6 +6983,14 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>
>  #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
>
> +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> +bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
> +{
> +       /* All shared VMAs have HGM enabled. */

Personally I find the comment redundant; the next line does just that.

What about VM_MAYSHARE? Should those also have HGM enabled?

Is it possible to get some docs with this series for V1? This would be
something to highlight in the docs.

> +       return vma->vm_flags & VM_SHARED;
> +}
> +#endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
> +
>  /*
>   * These functions are overwritable if your architecture needs its own
>   * behavior.
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>