On 3/18/20 3:15 PM, Dave Hansen wrote:
> Hi Mike,
>
> The series looks like a great idea to me. One nit on the x86 bits,
> though...
>
>> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
>> index 5bfd5aef5378..51e6208fdeec 100644
>> --- a/arch/x86/mm/hugetlbpage.c
>> +++ b/arch/x86/mm/hugetlbpage.c
>> @@ -181,16 +181,25 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>> #endif /* CONFIG_HUGETLB_PAGE */
>>
>> #ifdef CONFIG_X86_64
>> +bool __init arch_hugetlb_valid_size(unsigned long long size)
>> +{
>> + if (size == PMD_SIZE)
>> + return true;
>> + else if (size == PUD_SIZE && boot_cpu_has(X86_FEATURE_GBPAGES))
>> + return true;
>> + else
>> + return false;
>> +}
>
> I'm pretty sure it's possible to have a system without 2M/PMD page
> support. We even have a handy-dandy comment about it in
> arch/x86/include/asm/required-features.h:
>
> #ifdef CONFIG_X86_64
> #ifdef CONFIG_PARAVIRT
> /* Paravirtualized systems may not have PSE or PGE available */
> #define NEED_PSE 0
> ...
>
> I *think* you need an X86_FEATURE_PSE check here to be totally correct.
>
> if (size == PMD_SIZE && cpu_feature_enabled(X86_FEATURE_PSE))
> return true;
>
> BTW, I prefer cpu_feature_enabled() to boot_cpu_has() because it
> includes disabled-features checking. I don't think any of it matters
> for these specific features, but I generally prefer it on principle.
Sounds good. I'll incorporate those changes into a v2, unless someone
else with has a different opinion.
BTW, this patch should not really change the way the code works today.
It is mostly a movement of code. Unless I am missing something, the
existing code will always allow setup of PMD_SIZE hugetlb pages.
--
Mike Kravetz
