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

[Zi Yan]

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@xxxxxxxxxx>
---
 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