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

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Message-ID: <255ccf96-2c12-9ca0-9f8b-8a8461253952@linux.alibaba.com>
Date:   Thu, 16 Jun 2022 11:48:56 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Mike Kravetz <mike.kravetz@...cle.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 6/16/2022 5:22 AM, Mike Kravetz wrote:
> 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.

Sure. I've sent it out [1], and please fold it into your series. Thanks.

[1] 
https://lore.kernel.org/all/7256dbe078d7231f45b0f47c2c52a3bd3aa10da7.1655350193.git.baolin.wang@linux.alibaba.com/