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: <95bd9375-36d2-7e34-83a8-d9eedfe70956@oracle.com>
Date:   Tue, 31 May 2022 10:05:21 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Michal Hocko <mhocko@...e.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 5/30/22 19:04, Muchun Song wrote:
> On Mon, May 30, 2022 at 03:56:43PM -0400, Peter Xu wrote:
>> Hi, Mike,
>>
>> On Fri, May 27, 2022 at 03:58:47PM -0700, Mike Kravetz wrote:
>>> +unsigned long hugetlb_mask_last_hp(struct hstate *h)
>>> +{
>>> +	unsigned long hp_size = huge_page_size(h);
>>> +
>>> +	if (hp_size == P4D_SIZE)
>>> +		return PGDIR_SIZE - P4D_SIZE;
>>> +	else if (hp_size == PUD_SIZE)
>>> +		return P4D_SIZE - PUD_SIZE;
>>> +	else if (hp_size == PMD_SIZE)
>>> +		return PUD_SIZE - PMD_SIZE;
>>> +
>>> +	return ~(0);
>>> +}
>>
>> How about:
>>
>> unsigned long hugetlb_mask_last_hp(struct hstate *h)
>> {
>> 	unsigned long hp_size = huge_page_size(h);
>>
>> 	return hp_size * (PTRS_PER_PTE - 1);
>> }
>>
> 
> +1
>  


I like this as well, but I wonder if we should put something like the
following in just to be safe.

BUILD_BUG_ON(PTRS_PER_PTE != PTRS_PER_PMD);
BUILD_BUG_ON(PTRS_PER_PTE != PTRS_PER_PUD);
BUILD_BUG_ON(PTRS_PER_PTE != PTRS_PER_P4D);

-- 
Mike Kravetz