[PATCHv6 11/22] thp, mm: warn if we try to use replace_page_cache_page() with THP

[Kirill A. Shutemov]

replace_page_cache_page() is only used by FUSE. It's unlikely that we
will support THP in FUSE page cache any soon.

Let's pospone implemetation of THP handling in replace_page_cache_page()
until any will use it. -EINVAL and WARN_ONCE() for now.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/filemap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index 60478ebeda..3421bcaed4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -417,6 +417,10 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
 {
 	int error;
 
+	if (WARN_ONCE(PageTransHuge(old) || PageTransHuge(new),
+		     "unexpected transhuge page\n"))
+		return -EINVAL;
+
 	VM_BUG_ON(!PageLocked(old));
 	VM_BUG_ON(!PageLocked(new));
 	VM_BUG_ON(new->mapping);
-- 
1.8.4.rc3

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