[PATCH v2 2/2] smaps: set THPeligible if file mapping supports large folios

["Zach O'Keefe" <zokeefe@google.com>]

File-backed memory can be backed by THPs either through collapse, when
CONFIG_READ_ONLY_THP_FOR_FS is enabled, or through fault, when the
filesystem supports large folio mappings.

Currently, smaps only knows about the former, so teach it about the
latter.

Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
---
 mm/huge_memory.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cd379b2c077b..d8d6e83820f3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -136,7 +136,16 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
 			 */
 			!!vma->vm_ops->huge_fault :
 			/* Only regular file is valid in collapse path */
-			file_thp_enabled(vma);
+			file_thp_enabled(vma) ||
+			 /*
+			  * THPeligible bit of smaps should surface the
+			  * possibility of THP through fault if the filesystem
+			  * supports it.  We don't check this in fault path,
+			  * because we want to fallback to the actual ->fault()
+			  * handler to make the decision.
+			  */
+			 (smaps && vma->vm_file &&
+			 mapping_large_folio_support(vma->vm_file->f_mapping));
 
 	if (vma_is_temporary_stack(vma))
 		return false;
-- 
2.42.0.rc1.204.g551eb34607-goog