Re: [PATCH v1 00/10] Remove READ_ONLY_THP_FOR_FS Kconfig

Zi Yan
2026-03-27T14:26:11Z

On 27 Mar 2026, at 9:46, David Hildenbrand (Arm) wrote:

> On 3/27/26 02:42, Zi Yan wrote:
>> Hi all,
>>
>> This patchset removes READ_ONLY_THP_FOR_FS Kconfig and enables creating
>> read-only THPs for FSes with large folio support (the supported orders
>> need to include PMD_ORDER) by default.
>>
>> The changes are:
>> 1. collapse_file() from mm/khugepaged.c, instead of checking
>> CONFIG_READ_ONLY_THP_FOR_FS, makes sure the mapping_max_folio_order()
>> of struct address_space of the file is at least PMD_ORDER.
>> 2. file_thp_enabled() also checks mapping_max_folio_order() instead.
>> 3. truncate_inode_partial_folio() calls folio_split() directly instead
>> of the removed try_folio_split_to_order(), since large folios can
>> only show up on a FS with large folio support.
>> 4. nr_thps is removed from struct address_space, since it is no longer
>> needed to drop all read-only THPs from a FS without large folio
>> support when the fd becomes writable. Its related filemap_nr_thps*()
>> are removed too.
>> 5. folio_check_splittable() no longer checks READ_ONLY_THP_FOR_FS.
>> 6. Updated comments in various places.
>>
>> Changelog
>> ===
>> From RFC[1]:
>> 1. instead of removing READ_ONLY_THP_FOR_FS function entirely, turn it
>> on by default for all FSes with large folio support and the supported
>> orders includes PMD_ORDER.
>>
>> Suggestions and comments are welcome.
>
> Hi! :)
>
> The patch set might be better structured by
>
> 1) Teaching code paths to not only respect READ_ONLY_THP_FOR_FS but also
> filesystems with large folios. At that point, READ_ONLY_THP_FOR_FS would
> have no effect.
>
> 2) Removing READ_ONLY_THP_FOR_FS along with all the old cruft that is no
> longer required
>
> MADV_COLLAPSE will keep working the whole time.

OK. I will give this a try.

Best Regards,
Yan, Zi