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

From: Mike Kravetz <mike.kravetz@oracle.com>
To: Muchun Song <songmuchun@bytedance.com>, Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Michal Hocko <mhocko@suse.com>,
	Naoya Horiguchi <naoya.horiguchi@linux.dev>,
	James Houghton <jthoughton@google.com>,
	Mina Almasry <almasrymina@google.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH 1/3] hugetlb: skip to end of PT page mapping when pte not present
Date: Tue, 31 May 2022 10:05:21 -0700	[thread overview]
Message-ID: <95bd9375-36d2-7e34-83a8-d9eedfe70956@oracle.com> (raw)
In-Reply-To: <YpV3qrSHGsIuvifX@FVFYT0MHHV2J.googleapis.com>

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