Le 23/01/2024 à 12:38, Ryan Roberts a écrit :
> On 23/01/2024 11:31, David Hildenbrand wrote:
>>>>
>>>>> If high bits are used for
>>>>> something else, then we might produce a garbage PTE on overflow, but that
>>>>> shouldn't really matter I concluded for folio_pte_batch() purposes, we'd not
>>>>> detect "belongs to this folio batch" either way.
>>>>
>>>> Exactly.
>>>>
>>>>>
>>>>> Maybe it's likely cleaner to also have a custom pte_next_pfn() on ppc, I just
>>>>> hope that we don't lose any other arbitrary PTE bits by doing the pte_pgprot().
>>>>
>>>> I don't see the need for ppc to implement pte_next_pfn().
>>>
>>> Agreed.
>>
>> So likely we should then do on top for powerpc (whitespace damage):
>>
>> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
>> index a04ae4449a025..549a440ed7f65 100644
>> --- a/arch/powerpc/mm/pgtable.c
>> +++ b/arch/powerpc/mm/pgtable.c
>> @@ -220,10 +220,7 @@ void set_ptes(struct mm_struct *mm, unsigned long addr,
>> pte_t *ptep,
>> break;
>> ptep++;
>> addr += PAGE_SIZE;
>> - /*
>> - * increment the pfn.
>> - */
>> - pte = pfn_pte(pte_pfn(pte) + 1, pte_pgprot((pte)));
>> + pte = pte_next_pfn(pte);
>> }
>> }
>
> Looks like commit 47b8def9358c ("powerpc/mm: Avoid calling
> arch_enter/leave_lazy_mmu() in set_ptes") changed from doing the simple
> increment to this more complex approach, but the log doesn't say why.
Right. There was a discussion about it without any conclusion:
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20231024143604.16749-1-aneesh.kumar@xxxxxxxxxxxxx/
As far as understand the simple increment is better on ppc/32 but worse
in ppc/64.
Christophe
