On 27 Mar 2026, at 10:27, Lorenzo Stoakes (Oracle) wrote: > On Fri, Mar 27, 2026 at 02:46:43PM +0100, 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. > > And also please do some cleaning up of the mess we have in the code base if at > all possible :) I feel like we're constantly building on sand with this, and > should treat every major change as a chance to do this. > > Or otherwise we constantly keep leaving this mess around to deal with...
Got it. Let me read through feedbacks from individual patches and come up with a plan. > >> >> 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. > > Obviously everything should keep working throughout any version of this > series. > Ack. Best Regards, Yan, Zi
