mm: fix warning in __set_page_dirty_nobuffers

New tmpfs use of !PageUptodate pages for fallocate() is triggering the
WARNING: at mm/page-writeback.c:1990 when __set_page_dirty_nobuffers()
is called from migrate_page_copy() for compaction.

It is anomalous that migration should use __set_page_dirty_nobuffers()
on an address_space that does not participate in dirty and writeback
accounting; and this has also been observed to insert surprising dirty
tags into a tmpfs radix_tree, despite tmpfs not using tags at all.

We should probably give migrate_page_copy() a better way to preserve the
tag and migrate accounting info, when mapping_cap_account_dirty().  But
that needs some more work: so in the interim, avoid the warning by using
a simple SetPageDirty on PageSwapBacked pages.

Reported-and-tested-by: Dave Jones <davej@redhat.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index ab81d48..be26d5c 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -436,7 +436,10 @@ void migrate_page_copy(struct page *newpage, struct page *page)
                 * is actually a signal that all of the page has become dirty.
                 * Whereas only part of our page may be dirty.
                 */
-               __set_page_dirty_nobuffers(newpage);
+               if (PageSwapBacked(page))
+                       SetPageDirty(newpage);
+               else
+                       __set_page_dirty_nobuffers(newpage);
        }
 
        mlock_migrate_page(newpage, page);