Re: [PATCH v1 01/10] mm: remove READ_ONLY_THP_FOR_FS Kconfig option

[Zi Yan <ziy@nvidia.com>]

On 27 Mar 2026, at 9:33, David Hildenbrand (Arm) wrote:

> On 3/27/26 02:42, Zi Yan wrote:
>> No one will be able to use it, so the related code can be removed in the
>> coming commits.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>>  mm/Kconfig | 11 -----------
>>  1 file changed, 11 deletions(-)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index bd283958d675..408fc7b82233 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -937,17 +937,6 @@ config THP_SWAP
>>
>>  	  For selection by architectures with reasonable THP sizes.
>>
>> -config READ_ONLY_THP_FOR_FS
>> -	bool "Read-only THP for filesystems (EXPERIMENTAL)"
>> -	depends on TRANSPARENT_HUGEPAGE
>> -
>> -	help
>> -	  Allow khugepaged to put read-only file-backed pages in THP.
>> -
>> -	  This is marked experimental because it is a new feature. Write
>> -	  support of file THPs will be developed in the next few release
>> -	  cycles.
>> -
>>  config NO_PAGE_MAPCOUNT
>>  	bool "No per-page mapcount (EXPERIMENTAL)"
>>  	help
>
> Isn't that usually what we do at the very end when we converted all the
> code?

The rationale is that after removing Kconfig, the related code is always
disabled and the following patches can remove it piece by piece. The approach
you are hinting at might be to 1) remove all users of READ_ONLY_THP_FOR_FS,
making collapse_file() reject FSes without large folio support, 2) remove
other READ_ONLY_THP_FOR_FS related code. It might still cause confusion
since READ_ONLY_THP_FOR_FS is still present while its functionality is gone.

But as you pointed out in the cover letter that MADV_COLLAPSE needs to
work throughout the patchset, I will move this patch in a later stage
when MADV_COLLAPSE works on FSes with large folio support.

WDYT?

Best Regards,
Yan, Zi