On 14 Apr 2026, at 11:43, Lance Yang wrote: > On Tue, Apr 14, 2026 at 11:37:24PM +0800, Lance Yang wrote: >> >> On Tue, Apr 14, 2026 at 12:29:04PM +0200, David Hildenbrand (Arm) wrote: >>> On 4/13/26 21:20, 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. >>>> >>>> In collapse_scan_file(), add FS eligibility check to avoid redundant scans. >>>> >>>> Signed-off-by: Zi Yan <[email protected]> >>>> --- >>>> mm/khugepaged.c | 12 ++++++++++-- >>>> 1 file changed, 10 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>>> index b8452dbdb043..d2f0acd2dac2 100644 >>>> --- a/mm/khugepaged.c >>>> +++ b/mm/khugepaged.c >>>> @@ -1892,8 +1892,9 @@ static enum scan_result collapse_file(struct >>>> mm_struct *mm, unsigned long addr, >>>> int nr_none = 0; >>>> bool is_shmem = shmem_file(file); >>>> >>>> - VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); >>>> - VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); >>>> + /* MADV_COLLAPSE ignores shmem huge config, so do not check shmem */ >>>> + VM_WARN_ON_ONCE(!is_shmem && mapping_max_folio_order(mapping) < >>>> PMD_ORDER); >>>> + VM_WARN_ON_ONCE(start & (HPAGE_PMD_NR - 1)); >>>> >>>> result = alloc_charge_folio(&new_folio, mm, cc); >>>> if (result != SCAN_SUCCEED) >>>> @@ -2321,6 +2322,13 @@ static enum scan_result collapse_scan_file(struct >>>> mm_struct *mm, >>>> int node = NUMA_NO_NODE; >>>> enum scan_result result = SCAN_SUCCEED; >>>> >>>> + /* >>>> + * skip files without PMD-order folio support >>>> + * do not check shmem, since MADV_COLLAPSE ignores shmem huge config >>>> + */ >>> >>> How is the !collapse path handled? Through thp_vma_allowable_order() in >>> collapse_scan_mm_slot()? >>> >>> Wouldn't it be better to have that check exactly there? >> >> Right! Looks like patch #03[1] already does that, as David also pointed >> out there :) >> >> With that in place, regular files should end up in file_thp_enabled(), >> which checks that mapping_max_folio_order() >= PMD_ORDER. > > Forgot to add: > > thp_vma_allowable_order() > -> file_thp_enabled() > -> mapping_max_folio_order() check > >> For khugepaged, collapse_scan_mm_slot() calls thp_vma_allowable_order() >> before entering the per-PMD scan loop, so ineligible regular file VMAs >> should already get filtered there. >> >> madvise_collapse() also calls thp_vma_allowable_order() early, so it >> should get the same filtering before reaching collapse_scan_file(). >> >> So the extra check here looks redundant :) >> >> [1] https://lore.kernel.org/linux-mm/[email protected]/ >>
Right. Will remove the extra check from collapse_scan_file(). Best Regards, Yan, Zi
