Re: [PATCH v2] mm: shmem: don't set large-order range for internal shmem mount

[Zi Yan]

On 15 Apr 2026, at 21:05, Baolin Wang wrote:

> On 4/15/26 10:36 PM, David Hildenbrand (Arm) wrote:
>> On 4/15/26 12:05, Baolin Wang wrote:
>>>
>>>
>>> On 4/15/26 5:54 PM, David Hildenbrand (Arm) wrote:
>>>>>
>>>>> Yes, that makes sense.
>>>>>
>>>>> However, it’s also possible that the mapping does not support large
>>>>> folios, yet anonymous shmem can still allocate large folios via the
>>>>> sysfs interfaces. That doesn't make sense, right?
>>>>
>>>> That's what I am saying: if there could be large folios in there, then
>>>> let's tell the world.
>>>>
>>>> Getting in a scenario where the mapping claims to not support large
>>>> folios, but then we have large folios in there is inconsistent, not?
>>>>
>>>> [...]
>>>>
>>>>>
>>>>> For the current anonymous shmem (tmpfs is already clear, no questions),
>>>>> I don’t think there will be any "will never have/does never allow"
>>>>> cases, because it can be changed dynamically via the sysfs interfaces.
>>>>
>>>> Right. It's about non-anon shmem with huge=off.
>>>>
>>>>>
>>>>> If we still want that logic, then for anonymous shmem we can treat it as
>>>>> always "might have large folios".
>>>
>>> OK. To resolve the confusion about 1, the logic should be changed as
>>> follows. Does that make sense to you?
>>>
>>> if (sbinfo->huge || (sb->s_flags & SB_KERNMOUNT))
>>>      mapping_set_large_folios(inode->i_mapping);
>>
>> I think that's better.
>
> Thanks for your valuable input.
>
> But has Willy says, maybe we can just
>> unconditionally set it and have it even simpler.
>
> However, for tmpfs mounts, we should still respect the 'huge=' mount option. See commit 5a90c155defa ("tmpfs: don't enable large folios if not supported").

Is it possible to get sbinfo->huge during tmpfs’s folio allocation time, so that
even if all tmpfs has mapping_set_large_folios() but sbinfo->huge can still
decide whether huge page will be allocated for a tmpfs?

Best Regards,
Yan, Zi