Clean up and export cancel_dirty_page() to modules

Make cancel_dirty_page() act more like all the other dirty and writeback
accounting functions: test for "mapping" being NULL, and do the
NR_FILE_DIRY accounting purely based on mapping_cap_account_dirty()).

Also, add it to the exports, so that modular filesystems can use it.

Acked-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 4a38dd1a4ce8..ecdfdcc50522 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -60,12 +60,16 @@ void cancel_dirty_page(struct page *page, unsigned int account_size)
                 WARN_ON(++warncount < 5);
         }
                 
-        if (TestClearPageDirty(page) && account_size &&
-                        mapping_cap_account_dirty(page->mapping)) {
-                dec_zone_page_state(page, NR_FILE_DIRTY);
-                task_io_account_cancelled_write(account_size);
+        if (TestClearPageDirty(page)) {
+                struct address_space *mapping = page->mapping;
+                if (mapping && mapping_cap_account_dirty(mapping)) {
+                        dec_zone_page_state(page, NR_FILE_DIRTY);
+                        if (account_size)
+                                task_io_account_cancelled_write(account_size);
+                }
         }
 }
+EXPORT_SYMBOL(cancel_dirty_page);
 
 /*
  * If truncate cannot remove the fs-private metadata from the page, the page