[PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

Zi Yan
2026-03-27T01:43:23Z

collapse_file() requires FSes supporting large folio with at least
PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with
huge option turned on also sets large folio order on mapping, so the check
also applies to shmem.

While at it, replace VM_BUG_ON with returning failure values.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
mm/khugepaged.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d06d84219e1b..45b12ffb1550 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1899,8 +1899,11 @@ 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));
+ /* "huge" shmem sets mapping folio order and passes the check below */
+ if (mapping_max_folio_order(mapping) < PMD_ORDER)
+ return SCAN_FAIL;
+ if (start & (HPAGE_PMD_NR - 1))
+ return SCAN_ADDRESS_RANGE;

result = alloc_charge_folio(&new_folio, mm, cc);
if (result != SCAN_SUCCEED)
--
2.43.0