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. 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]/ Cheers, Lance
