linux-kernel - Re: [PATCH v2 08/46] hugetlb: add HugeTLB HGM enablement helpers

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Date:   Fri, 24 Feb 2023 15:08:19 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Frank van der Linden <fvdl@...gle.com>,
        Jiaqi Yan <jiaqiyan@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/46] hugetlb: add HugeTLB HGM enablement helpers

On 02/18/23 00:27, James Houghton wrote:
> hugetlb_hgm_eligible indicates that a VMA is eligible to have HGM
> explicitly enabled via MADV_SPLIT, and hugetlb_hgm_enabled indicates
> that HGM has been enabled.
> 
> Signed-off-by: James Houghton <jthoughton@...gle.com>
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 7c977d234aba..efd2635a87f5 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -1211,6 +1211,20 @@ static inline void hugetlb_unregister_node(struct node *node)
>  }
>  #endif	/* CONFIG_HUGETLB_PAGE */
>  
> +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> +bool hugetlb_hgm_enabled(struct vm_area_struct *vma);
> +bool hugetlb_hgm_eligible(struct vm_area_struct *vma);
> +#else
> +static inline bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
> +{
> +	return false;
> +}
> +static inline bool hugetlb_hgm_eligible(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 6c008c9de80e..0576dcc98044 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -7004,6 +7004,10 @@ static bool pmd_sharing_possible(struct vm_area_struct *vma)
>  #ifdef CONFIG_USERFAULTFD
>  	if (uffd_disable_huge_pmd_share(vma))
>  		return false;
> +#endif
> +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> +	if (hugetlb_hgm_enabled(vma))
> +		return false;
>  #endif
>  	/*
>  	 * Only shared VMAs can share PMDs.
> @@ -7267,6 +7271,18 @@ __weak unsigned long hugetlb_mask_last_page(struct hstate *h)
>  
>  #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
>  
> +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> +bool hugetlb_hgm_eligible(struct vm_area_struct *vma)
> +{
> +	/* All shared VMAs may have HGM. */
> +	return vma && (vma->vm_flags & VM_MAYSHARE);

I think the only user is madvise_split().  We should probably check here
or more likely at the beginning of madvise_split for VM_HUGETLB_HGM already
set.  No sense in invoking the overhead of hugetlb_unshare_all_pmds if
not needed.
-- 
Mike Kravetz

> +}
> +bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
> +{
> +	return vma && (vma->vm_flags & VM_HUGETLB_HGM);
> +}
> +#endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
> +
>  /*
>   * These functions are overwritable if your architecture needs its own
>   * behavior.
> -- 
> 2.39.2.637.g21b0678d19-goog
>