On 24 Apr 2026, at 11:07, Zi Yan wrote: > On 24 Apr 2026, at 8:54, David Hildenbrand (Arm) wrote: > >> On 4/24/26 04:49, Zi Yan wrote: >>> After READ_ONLY_THP_FOR_FS is removed, FS either supports large folio or >>> not. folio_split() can be used on a FS with large folio support without >>> worrying about getting a THP on a FS without large folio support. >>> >>> When READ_ONLY_THP_FOR_FS was present, a PMD large pagecache folio can >>> appear in a FS without large folio support after khugepaged or >>> madvise(MADV_COLLAPSE) creates it. During truncate_inode_partial_folio(), >>> such a PMD large pagecache folio is split and if the FS does not support >>> large folio, it needs to be split to order-0 ones and could not be split >>> non uniformly to ones with various orders. try_folio_split_to_order() was >>> added to handle this situation by checking folio_check_splittable(..., >>> SPLIT_TYPE_NON_UNIFORM) to detect if the large folio is created due to >>> READ_ONLY_THP_FOR_FS and the FS does not support large folio. Now >>> READ_ONLY_THP_FOR_FS is removed, all large pagecache folios are created >>> with FSes supporting large folio, this function is no longer needed and all >>> large pagecache folios can be split non uniformly. >> >> In general looks good. Just one question: >> >> folio_check_splittable() also rejects SPLIT_TYPE_NON_UNIFORM / new_order for >> swapcache pages. > > Since swapcache only supports PMD order or 0 order yet. > >> >> It's confusing, but truncate would never stumble over such folios, correct? > > Right.
BTW, sashiko had a similar question when it reviewed v2[1]. It also complained about when the split fails, the entire folio remains in memory. But that is the consequence of failed split, unless we want to keep retrying the split. [1] https://sashiko.dev/#/patchset/20260413192030.3275825-1-ziy%40nvidia.com?part=9 Best Regards, Yan, Zi
