[PATCH] remove truncate mapped BUG

It's time to remove truncate_complete_page's BUG_ON(page_mapped(page)): it
was there to give confidence in the new vm_truncate_count mechanism. 
Earlier releases had no such check, and it wouldn't be at all helpful if it
ever bugged up file truncation on a production system - though we don't
know of any scenario in which that could happen now.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/truncate.c

@@ -45,7 +45,6 @@ static inline void truncate_partial_page(struct page *page, unsigned partial)
 static void
 truncate_complete_page(struct address_space *mapping, struct page *page)
 {
-	BUG_ON(page_mapped(page));
 	if (page->mapping != mapping)
 		return;