---

yaml
---
r: 45814
b: refs/heads/master
c: ecdfc97
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5ad0d383ddbf0d2fce43b8aac267a6c299fd2dff
+refs/heads/master: ecdfc9787fe527491baefc22dce8b2dbd5b2908d

trunk/fs/buffer.c

@@ -2834,7 +2834,7 @@ int try_to_free_buffers(struct page *page)
 	int ret = 0;
 
 	BUG_ON(!PageLocked(page));
-	if (PageDirty(page) || PageWriteback(page))
+	if (PageWriteback(page))
 		return 0;
 
 	if (mapping == NULL) {		/* can this still happen? */
@@ -2845,6 +2845,19 @@ int try_to_free_buffers(struct page *page)
 	spin_lock(&mapping->private_lock);
 	ret = drop_buffers(page, &buffers_to_free);
 	spin_unlock(&mapping->private_lock);
+
+	/*
+	 * If the filesystem writes its buffers by hand (eg ext3)
+	 * then we can have clean buffers against a dirty page.  We
+	 * clean the page here; otherwise the VM will never notice
+	 * that the filesystem did any IO at all.
+	 *
+	 * Also, during truncate, discard_buffer will have marked all
+	 * the page's buffers clean.  We discover that here and clean
+	 * the page also.
+	 */
+	if (ret)
+		cancel_dirty_page(page, PAGE_CACHE_SIZE);
 out:
 	if (buffers_to_free) {
 		struct buffer_head *bh = buffers_to_free;

trunk/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)) {