On 5 Apr 2026, at 13:38, Nico Pache wrote: > On Thu, Mar 26, 2026 at 7:43 PM Zi Yan <[email protected]> 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. > > Hi Zi, > > Thank you for tackling this :) Ill try to review the next version as > I'm a little behind on this thread.
Sure. Thanks. > > Should we guard collapsing READ_ONLY_THPs with a sysctl? My fear is > workloads that convert READ_ONLY THPs into writable pages (assuming > this is common/possible; my understanding of FS is rather low), > leading to storms of thp splitting. Do you think this is a real > concern? I guess this is also true of read-only-->writable fs-THPS > even without khugepaged, correct? Why would a read-only THP need to be split when it becomes writable? After this patchset, a read-only THP can only be created on a FS that supports large folios (to be precise PMD THP). That means any write to that read-only THP would just change it to a writable THP. Let me know if I miss anything. > > Cheers, > -- Nico > >> >> 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. >> >> Link: https://lore.kernel.org/all/[email protected]/ >> [1] >> >> Zi Yan (10): >> mm: remove READ_ONLY_THP_FOR_FS Kconfig option >> mm/khugepaged: remove READ_ONLY_THP_FOR_FS check >> mm: fs: remove filemap_nr_thps*() functions and their users >> fs: remove nr_thps from struct address_space >> mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled() >> mm/huge_memory: remove folio split check for READ_ONLY_THP_FOR_FS >> mm/truncate: use folio_split() in truncate_inode_partial_folio() >> fs/btrfs: remove a comment referring to READ_ONLY_THP_FOR_FS >> selftests/mm: remove READ_ONLY_THP_FOR_FS in khugepaged >> selftests/mm: remove READ_ONLY_THP_FOR_FS from comments in >> guard-regions >> >> fs/btrfs/defrag.c | 3 -- >> fs/inode.c | 3 -- >> fs/open.c | 27 ---------------- >> include/linux/fs.h | 5 --- >> include/linux/huge_mm.h | 25 ++------------- >> include/linux/pagemap.h | 29 ----------------- >> mm/Kconfig | 11 ------- >> mm/filemap.c | 1 - >> mm/huge_memory.c | 29 ++--------------- >> mm/khugepaged.c | 36 +++++----------------- >> mm/truncate.c | 8 ++--- >> tools/testing/selftests/mm/guard-regions.c | 9 +++--- >> tools/testing/selftests/mm/khugepaged.c | 4 +-- >> 13 files changed, 23 insertions(+), 167 deletions(-) >> >> -- >> 2.43.0 >> -- Best Regards, Yan, Zi
