Re: [RFC PATCH 1/5] hugetlb: add hugetlb helpers for soft dirty support

[Mike Kravetz]

On 2/17/21 8:24 AM, Peter Xu wrote:
> On Wed, Feb 10, 2021 at 04:03:18PM -0800, Mike Kravetz wrote:
>> Add interfaces to set and clear soft dirty in hugetlb ptes.  Make
>> hugetlb interfaces needed for /proc clear_refs available outside
>> hugetlb.c.
>>
>> arch/s390 has it's own version of most routines in asm-generic/hugetlb.h,
>> so add new routines there as well.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>> ---
>>  arch/s390/include/asm/hugetlb.h | 30 ++++++++++++++++++++++++++++++
>>  include/asm-generic/hugetlb.h   | 30 ++++++++++++++++++++++++++++++
>>  include/linux/hugetlb.h         |  1 +
>>  mm/hugetlb.c                    | 10 +---------
>>  4 files changed, 62 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/hugetlb.h b/arch/s390/include/asm/hugetlb.h
>> index 60f9241e5e4a..b7d26248fb1c 100644
>> --- a/arch/s390/include/asm/hugetlb.h
>> +++ b/arch/s390/include/asm/hugetlb.h
>> @@ -105,6 +105,11 @@ static inline pte_t huge_pte_mkdirty(pte_t pte)
>>  	return pte_mkdirty(pte);
>>  }
>>  
>> +static inline pte_t huge_pte_mkyoung(pte_t pte)
>> +{
>> +	return pte_mkyoung(pte);
>> +}
>> +
>>  static inline pte_t huge_pte_wrprotect(pte_t pte)
>>  {
>>  	return pte_wrprotect(pte);
>> @@ -115,9 +120,34 @@ static inline pte_t huge_pte_modify(pte_t pte, pgprot_t newprot)
>>  	return pte_modify(pte, newprot);
>>  }
>>  
>> +static inline bool huge_pte_soft_dirty(pte_t pte)
>> +{
>> +	return pte_soft_dirty(pte);
>> +}
>> +
>> +static inline pte_t huge_pte_clear_soft_dirty(pte_t pte)
>> +{
>> +	return pte_clear_soft_dirty(pte);
>> +}
>> +
>> +static inline pte_t huge_pte_swp_clear_soft_dirty(pte_t pte)
>> +{
>> +	return pte_swp_clear_soft_dirty(pte);
>> +}
>> +
> 
> Indeed asm/hugetlb.h of s390 didn't include asm-generic/hugetlb.h as what was
> normally done by asm/hugetlb.h of other archs.  Do you know why it's special?
> E.g. huge_pte_wrprotect() of s390 version is actually the same of the default
> version.
> 
> When I looked at the huge_pte_wrprotect() I also see that there seems to have
> no real user of __HAVE_ARCH_HUGE_PTE_WRPROTECT.  Not sure whether it can be
> dropped.  My gut feeling is that s390 should also include asm-generic/hugetlb.h
> but only redefine the helper only if necessary, since I see no point defining
> the same helper multiple times.

I do not know why s390 is special in this way.  However, I did cc some s390
people and the list.  Perhaps they know?

> 
>>  static inline bool gigantic_page_runtime_supported(void)
>>  {
>>  	return true;
>>  }
>>  
>> +#if !defined(__HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE) && !defined(MODULE)
>> +#include <asm/tlbflush.h>
>> +
>> +static inline void flush_hugetlb_tlb_range(struct vm_area_struct *vma,
>> +					unsigned long start, unsigned long end)
>> +{
>> +	flush_tlb_range(vma, start, end);
>> +}
>> +#endif
> 
> Similar question here, only ppc defined __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE, so
> IIUC it means s390 should simply use the default version, and it'll be great if
> we don't need to redefine it here.

Actually, your patch "mm/hugetlb: Move flush_hugetlb_tlb_range() into
hugetlb.h" makes this change unnecessary.  But, the question about ppc
remains.
-- 
Mike Kravetz