linux-kernel - Re: [RFC PATCH 1/3] hugetlb: skip to end of PT page mapping when pte not present

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Date:   Wed, 15 Jun 2022 14:22:34 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Muchun Song <songmuchun@...edance.com>,
        Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        James Houghton <jthoughton@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 1/3] hugetlb: skip to end of PT page mapping when pte
 not present

On 05/30/22 18:10, Baolin Wang wrote:
> 
> 
> On 5/28/2022 6:58 AM, Mike Kravetz wrote:
> > HugeTLB address ranges are linearly scanned during fork, unmap and
> > remap operations.  If a non-present entry is encountered, the code
> > currently continues to the next huge page aligned address.  However,
> > a non-present entry implies that the page table page for that entry
> > is not present.  Therefore, the linear scan can skip to the end of
> > range mapped by the page table page.  This can speed operations on
> > large sparsely populated hugetlb mappings.
> > 
> > Create a new routine hugetlb_mask_last_hp() that will return an
> > address mask.  When the mask is ORed with an address, the result
> > will be the address of the last huge page mapped by the associated
> > page table page.  Use this mask to update addresses in routines which
> > linearly scan hugetlb address ranges when a non-present pte is
> > encountered.
> > 
> > hugetlb_mask_last_hp is related to the implementation of huge_pte_offset
> > as hugetlb_mask_last_hp is called when huge_pte_offset returns NULL.
> > This patch only provides a complete hugetlb_mask_last_hp implementation
> > when CONFIG_ARCH_WANT_GENERAL_HUGETLB is defined.  Architectures which
> > provide their own versions of huge_pte_offset can also provide their own
> > version of hugetlb_mask_last_hp.
> 
> I tested on my ARM64 machine with implementing arm64 specific
> hugetlb_mask_last_hp() as below, and it works well.
> 
> Just a few nits inline, otherwise looks good to me.
> Tested-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index d93ba128a2b0..e04a097ffcc4 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -376,6 +376,28 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>         return NULL;
>  }
> 
> +unsigned long hugetlb_mask_last_hp(struct hstate *h)
> +{
> +       unsigned long hp_size = huge_page_size(h);
> +
> +       switch (hp_size) {
> +       case P4D_SIZE:
> +               return PGDIR_SIZE - P4D_SIZE;
> +       case PUD_SIZE:
> +               return P4D_SIZE - PUD_SIZE;
> +       case CONT_PMD_SIZE:
> +               return PUD_SIZE - CONT_PMD_SIZE;
> +       case PMD_SIZE:
> +               return PUD_SIZE - PMD_SIZE;
> +       case CONT_PTE_SIZE:
> +               return PMD_SIZE - CONT_PTE_SIZE;
> +       default:
> +               break;
> +       }
> +
> +       return ~(0UL);
> +}

Hello Baolin,

Would you mind sending this as a proper patch with commit message and
'Signed-off-by:'?  I would like to include it in the upcoming patch series.

-- 
Mike Kravetz