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?
