Re: [PATCH] mm: madvise: make MADV_NOHUGEPAGE a no-op if !THP

[Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@kuka.com>]

On 5/14/2025 10:15 PM, James Houghton wrote:
> On Thu, May 8, 2025 at 3:20 AM Ignacio Moreno Gonzalez via B4 Relay
> <devnull+Ignacio.MorenoGonzalez.kuka.com@kernel.org> wrote:
>>
>> From: Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@kuka.com>
>>
>> VM_NOHUGEPAGE is a no-op if CONFIG_TRANSPARENT_HUGEPAGE is disabled. So
>> it makes no sense to return an error when calling madvise() with
>> MADV_NOHUGEPAGE in that case.
>>
>> Suggested-by: Matthew Wilcox <willy@infradead.org>
>> Signed-off-by: Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@kuka.com>
>> ---
>> https://lore.kernel.org/linux-mm/20250502-map-map_stack-to-vm_nohugepage-only-if-thp-is-enabled-v1-1-113cc634cd51@kuka.com
>>
>> Here it is presented as a separate thread to avoid mixing stable and
>> non-stable patches.
>>
>> This change makes calling madvise(addr, size, MADV_NOHUGEPAGE) on !THP
>> kernels to return 0 instead of -EINVAL.
>> ---
>>  include/linux/huge_mm.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index e893d546a49f464f7586db639fe216231f03651a..5fca742dc5ba784ffccea055b07247707d16cc67 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -509,6 +509,8 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
>>
>>  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>>
>> +#include <uapi/asm/mman.h>
>> +
>>  static inline bool folio_test_pmd_mappable(struct folio *folio)
>>  {
>>         return false;
>> @@ -598,6 +600,9 @@ static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma,
>>  static inline int hugepage_madvise(struct vm_area_struct *vma,
>>                                    unsigned long *vm_flags, int advice)
>>  {
>> +       /* On a !THP kernel, MADV_NOHUGEPAGE is a no-op, but MADV_NOHUGEPAGE is not supported */
> 
> Do you mean "but MADV_HUGEPAGE is not supported"? Just want to make
> sure; it seems like no one else has asked about this yet.
>

Yes, this is a typo. It should be MADV_HUGEPAGE. Thanks!

>> +       if (advice == MADV_NOHUGEPAGE)
>> +               return 0;
>>         return -EINVAL;
>>  }
>