Resurrect 'try_to_free_buffers()' VM hackery
It's not pretty, but it appears that ext3 with data=journal will clean
pages without ever actually telling the VM that they are clean. This,
in turn, will result in the VM (and balance_dirty_pages() in particular)
to never realize that the pages got cleaned, and wait forever for an
event that already happened.
Technically, this seems to be a problem with ext3 itself, but it used to
be hidden by 'try_to_free_buffers()' noticing this situation on its own,
and just working around the filesystem problem.
This commit re-instates that hack, in order to avoid a regression for
the 2.6.20 release. This fixes bugzilla 7844:
http://bugzilla.kernel.org/show_bug.cgi?id=7844
Peter Zijlstra points out that we should probably retain the debugging
code that this removes from cancel_dirty_page(), and I agree, but for
the imminent release we might as well just silence the warning too
(since it's not a new bug: anything that triggers that warning has been
around forever).
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/buffer.c b/fs/buffer.c
index 3b11607..460f1c4 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2834,7 +2834,7 @@
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 @@
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;
