1 files changed, 14 insertions, 7 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 6c79ca4a1ca7..3262740aa059 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -51,15 +51,22 @@ static inline void truncate_partial_page(struct page *page, unsigned partial)
                 do_invalidatepage(page, partial);
 }
 
+/*
+ * This cancels just the dirty bit on the kernel page itself, it
+ * does NOT actually remove dirty bits on any mmap's that may be
+ * around. It also leaves the page tagged dirty, so any sync
+ * activity will still find it on the dirty lists, and in particular,
+ * clear_page_dirty_for_io() will still look at the dirty bits in
+ * the VM.
+ *
+ * Doing this should *normally* only ever be done when a page
+ * is truncated, and is not actually mapped anywhere at all. However,
+ * fs/buffer.c does this when it notices that somebody has cleaned
+ * out all the buffers on a page without actually doing it through
+ * the VM. Can you say "ext3 is horribly ugly"? Tought you could.
+ */
 void cancel_dirty_page(struct page *page, unsigned int account_size)
 {
-        /* If we're cancelling the page, it had better not be mapped any more */
-        if (page_mapped(page)) {
-                static unsigned int warncount;
-
-                WARN_ON(++warncount < 5);
-        }
-                
         if (TestClearPageDirty(page)) {
                 struct address_space *mapping = page->mapping;
                 if (mapping && mapping_cap_account_dirty(mapping)) {