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

[David Hildenbrand (Arm)]

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. But has Willy says, maybe we can just
unconditionally set it and have it even simpler.

-- 
Cheers,

David