Re: [PATCH v1 05/10] mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled()

[Zi Yan]

On 27 Mar 2026, at 8:42, Lorenzo Stoakes (Oracle) wrote:

> On Thu, Mar 26, 2026 at 09:42:50PM -0400, Zi Yan wrote:
>> Replace it with a check on the max folio order of the file's address space
>> mapping, making sure PMD_ORDER is supported.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> ---
>>  mm/huge_memory.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index c7873dbdc470..1da1467328a3 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -89,9 +89,6 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
>>  {
>>  	struct inode *inode;
>>
>> -	if (!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS))
>> -		return false;
>> -
>>  	if (!vma->vm_file)
>>  		return false;
>>
>> @@ -100,6 +97,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
>>  	if (IS_ANON_FILE(inode))
>>  		return false;
>>
>> +	if (mapping_max_folio_order(inode->i_mapping) < PMD_ORDER)
>> +		return false;
>> +
>
> At this point I think this should be a separate function quite honestly and
> share it with 2/10's use, and then you can put the comment in here re: anon
> shmem etc.
>
> Though that won't apply here of course as shmem_allowable_huge_orders() would
> have been invoked :)
>
> But no harm in refactoring it anyway, and the repetitive < PMD_ORDER stuff is
> unfortunate.
>
> Buuut having said that is this right actually?
>
> Because we have:
>
> 		if (((in_pf || smaps)) && vma->vm_ops->huge_fault)
> 			return orders;
>
> Above it, and now you're enabling huge folio file systems to do non-page fault
> THP and that's err... isn't that quite a big change?

That is what READ_ONLY_THP_FOR_FS does, creating THPs after page faults, right?
This patchset changes the condition from all FSes to FSes with large folio
support.

Will add a helper, mapping_support_pmd_folio(), for
mapping_max_folio_order(inode->i_mapping) < PMD_ORDER.

>
> So yeah probably no to this patch as is :) we should just drop
> file_thp_enabled()?



>
>>  	return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
>>  }
>>
>> --
>> 2.43.0
>>


Best Regards,
Yan, Zi