[PATCH v5 01/14] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Zi Yan <ziy@nvidia.com>]

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.

Add a helper function mapping_pmd_folio_support() for FSes supporting large
folio with at least PMD_ORDER.

Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 include/linux/pagemap.h | 26 ++++++++++++++++++++++++++
 mm/khugepaged.c         | 10 ++++++++--
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 1f50991b43e3b..1fed3414fe9b8 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -513,6 +513,32 @@ static inline bool mapping_large_folio_support(const struct address_space *mappi
 	return mapping_max_folio_order(mapping) > 0;
 }
 
+/**
+ * mapping_pmd_folio_support() - Check if a mapping support PMD-sized folio
+ * @mapping: The address_space
+ *
+ * Some file supports large folio but does not support as large as PMD order.
+ * If a PMD-sized pagecache folio is attempted to be created on a filesystem,
+ * this check needs to be performed first.
+ *
+ * Return: true - PMD-sized folio is supported, false - PMD-sized folio is not
+ * supported.
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
+{
+	/* AS_FOLIO_ORDER is only reasonable for pagecache folios */
+	VM_WARN_ON_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON);
+
+	return mapping_max_folio_order(mapping) >= PMD_ORDER;
+}
+#else
+static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
+{
+	return false;
+}
+#endif
+
 /* Return the maximum folio size for this pagecache mapping, in bytes. */
 static inline size_t mapping_max_folio_size(const struct address_space *mapping)
 {
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e112525c4aa9c..6808f2b48d864 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2235,8 +2235,14 @@ 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
+	 *
+	 * TODO: once shmem always calls mapping_set_large_folios() on its
+	 * mapping, the shmem check can be removed.
+	 */
+	VM_WARN_ON_ONCE(!is_shmem && !mapping_pmd_folio_support(mapping));
+	VM_WARN_ON_ONCE(start & (HPAGE_PMD_NR - 1));
 
 	result = alloc_charge_folio(&new_folio, mm, cc, HPAGE_PMD_ORDER);
 	if (result != SCAN_SUCCEED)
-- 
2.53.0