[PATCH 7.2 v2 01/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

Zi Yan
2026-04-13T19:20:48Z

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 <ziy@nvidia.com>
---
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
+ */
+ if (!shmem_file(file) && mapping_max_folio_order(mapping) < PMD_ORDER)
+ return SCAN_FAIL;
+
present = 0;
swap = 0;
memset(cc->node_load, 0, sizeof(cc->node_load));
--
2.43.0