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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

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").