linux-kernel - Re: [PATCH 1/4] mm/hugetlb: Enable PUD level huge page migration

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Date:   Tue, 2 Oct 2018 18:26:49 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     punit.agrawal@....com, will.deacon@....com, Steven.Price@....com,
        catalin.marinas@....com, mhocko@...nel.org,
        mike.kravetz@...cle.com, n-horiguchi@...jp.nec.com
Subject: Re: [PATCH 1/4] mm/hugetlb: Enable PUD level huge page migration



On 10/02/2018 06:08 PM, Suzuki K Poulose wrote:
> Hi Anshuman
> 
> On 02/10/18 13:15, Anshuman Khandual wrote:
>> Architectures like arm64 have PUD level HugeTLB pages for certain configs
>> (1GB huge page is PUD based on ARM64_4K_PAGES base page size) that can be
>> enabled for migration. It can be achieved through checking for PUD_SHIFT
>> order based HugeTLB pages during migration.
>>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>   include/linux/hugetlb.h | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>> index 6b68e34..9c1b77f 100644
>> --- a/include/linux/hugetlb.h
>> +++ b/include/linux/hugetlb.h
>> @@ -483,7 +483,8 @@ static inline bool hugepage_migration_supported(struct hstate *h)
>>   {
>>   #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>>       if ((huge_page_shift(h) == PMD_SHIFT) ||
>> -        (huge_page_shift(h) == PGDIR_SHIFT))
>> +        (huge_page_shift(h) == PUD_SHIFT) ||
> 
> 
>> +            (huge_page_shift(h) == PGDIR_SHIFT))
> 
> nit: Extra Tab ^^.

The tab is in there when you apply this patch and all three checks are tab separated
in a newline.

> Also, if only arm64 supports PUD_SHIFT, should this be added only in the arm64 specific backend, which we introduce later ?

Even if with the platform can add this up in the back end, I would think having this
on for default fall back function makes it complete.