On 7 May 2026, at 11:29, Lance Yang wrote: > On Sun, May 03, 2026 at 09:48:40PM -0600, Nico Pache wrote: >> >> >> On 4/29/26 9:29 AM, Zi Yan wrote: >>> collapse_file() requires FSes supporting large folio with at least >>> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. >>> MADV_COLLAPSE ignores shmem huge config, so exclude the check for shmem. >>> >>> While at it, replace VM_BUG_ON with VM_WARN_ON_ONCE. >>> >>> Add a helper function mapping_pmd_folio_support() for FSes supporting large >>> folio with at least PMD_ORDER. >>> >>> Signed-off-by: Zi Yan <[email protected]> >>> Reviewed-by: Lance Yang <[email protected]> >>> Reviewed-by: Baolin Wang <[email protected]> >>> --- >>> include/linux/pagemap.h | 26 ++++++++++++++++++++++++++ >>> mm/khugepaged.c | 10 ++++++++-- >>> 2 files changed, 34 insertions(+), 2 deletions(-) >>> >>> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h >>> index 1f50991b43e3b..1fed3414fe9b8 100644 >>> --- a/include/linux/pagemap.h >>> +++ b/include/linux/pagemap.h >>> @@ -513,6 +513,32 @@ static inline bool mapping_large_folio_support(const >>> struct address_space *mappi >>> return mapping_max_folio_order(mapping) > 0; >>> } >>> >>> +/** >>> + * mapping_pmd_folio_support() - Check if a mapping support PMD-sized folio >>> + * @mapping: The address_space >>> + * >>> + * Some file supports large folio but does not support as large as PMD >>> order. >>> + * If a PMD-sized pagecache folio is attempted to be created on a >>> filesystem, >>> + * this check needs to be performed first. >>> + * >>> + * Return: true - PMD-sized folio is supported, false - PMD-sized folio is >>> not >>> + * supported. >>> + */ >>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> +static inline bool mapping_pmd_folio_support(const struct address_space >>> *mapping) >>> +{ >>> + /* AS_FOLIO_ORDER is only reasonable for pagecache folios */ >>> + VM_WARN_ON_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON); >>> + >>> + return mapping_max_folio_order(mapping) >= PMD_ORDER; >> >> Probably a stupid question, but I dont know FS thats well. >> >> Here we are checking that the max allowed folio order is greater than >> (or eq) to the PMD_ORDER. Yet the function asks if PMD specifically is >> supported. In the future could we have some FS that does not support PMD >> orders, but does support larger orders (eg. PUD)? > > Good point. > > IIUC, mapping_max_folio_order() means "maximum supported order" not > "the only supported order", so mapping_pmd_folio_support() just means > "PMD order is within the supported range". > > Also, mapping_set_large_folios() sets the range to: > > mapping_set_folio_order_range(mapping, 0, MAX_PAGECACHE_ORDER); > > and __filemap_get_folio_mpol() treats max as a cap, then falls back down > towards min. > > That said, if we want the helper name to mean "PMD order specifically is > supported", the more future-proof test would be: > > mapping_min_folio_order(mapping) <= PMD_ORDER && > mapping_max_folio_order(mapping) >= PMD_ORDER > > Thoughs?
Thank both for raising this up. I agree just <= PMD_ORDER might not cover the exact requirement here. Let me send a fixup. Best Regards, Yan, Zi
