Re: [PATCHv6 06/17] LoongArch/mm: Align vmemmap to maximal folio size

David Hildenbrand (Arm)
2026-02-05T13:57:32Z

On 2/5/26 14:52, Kiryl Shutsemau wrote:
> On Wed, Feb 04, 2026 at 05:56:45PM +0100, David Hildenbrand (arm) wrote:
>> On 2/2/26 16:56, Kiryl Shutsemau wrote:
>>> The upcoming change to the HugeTLB vmemmap optimization (HVO) requires
>>> struct pages of the head page to be naturally aligned with regard to the
>>> folio size.
>>>
>>> Align vmemmap to MAX_FOLIO_NR_PAGES.
>>>
>>> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
>>> ---
>>> arch/loongarch/include/asm/pgtable.h | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
>>> index c33b3bcb733e..f9416acb9156 100644
>>> --- a/arch/loongarch/include/asm/pgtable.h
>>> +++ b/arch/loongarch/include/asm/pgtable.h
>>> @@ -113,7 +113,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
>>> min(PTRS_PER_PGD * PTRS_PER_PUD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE, (1UL << cpu_vabits) / 2) - PMD_SIZE - VMEMMAP_SIZE - KFENCE_AREA_SIZE)
>>> #endif
>>> -#define vmemmap ((struct page *)((VMALLOC_END + PMD_SIZE) & PMD_MASK))
>>> +#define VMEMMAP_ALIGN max(PMD_SIZE, MAX_FOLIO_NR_PAGES * sizeof(struct page))
>>> +#define vmemmap ((struct page *)(ALIGN(VMALLOC_END, VMEMMAP_ALIGN)))
>>
>>
>> Same comment, the "MAX_FOLIO_NR_PAGES * sizeof(struct page)" is just black magic here
>> and the description of the situation is wrong.
>>
>> Maybe you want to pull the magic "MAX_FOLIO_NR_PAGES * sizeof(struct page)" into the core and call it
>>
>> #define MAX_FOLIO_VMEMMAP_ALIGN (MAX_FOLIO_NR_PAGES * sizeof(struct page))
>>
>> But then special case it base on (a) HVO being configured in an (b) HVO being possible
>>
>> #ifdef HUGETLB_PAGE_OPTIMIZE_VMEMMAP && is_power_of_2(sizeof(struct page)
>
> This would require some kind of asm-offsets.c/bounds.c magic to pull the
> struct page size condition to the preprocessor level.
>

Right.

I guess you could move that into the macro and let the compiler handle it.

--
Cheers,

David