[patch 11/47] write-back: fix nr_to_write counter

Greg KH
2009-02-14T01:05:38Z

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2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

commit dcf6a79dda5cc2a2bec183e50d829030c0972aaa upstream.

Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 introduced some
@wbc->nr_to_write breakage.

It made the following changes:
1. Decrement wbc->nr_to_write instead of nr_to_write
2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE
3. If synced nr_to_write pages, stop only if if wbc->sync_mode ==
WB_SYNC_NONE, otherwise keep going.

However, according to the commit message, the intention was to only make
change 3. Change 1 is a bug. Change 2 does not seem to be necessary,
and it breaks UBIFS expectations, so if needed, it should be done
separately later. And change 2 does not seem to be documented in the
commit message.

This patch does the following:
1. Undo changes 1 and 2
2. Add a comment explaining change 3 (it very useful to have comments
in _code_, not only in the commit).

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
mm/page-writeback.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)

--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -985,13 +985,22 @@ continue_unlock:
}
}

- if (wbc->sync_mode == WB_SYNC_NONE) {
+ if (wbc->nr_to_write > 0)
wbc->nr_to_write--;
- if (wbc->nr_to_write <= 0) {
- done = 1;
- break;
- }
+ else if (wbc->sync_mode == WB_SYNC_NONE) {
+ /*
+ * We stop writing back only if we are not
+ * doing integrity sync. In case of integrity
+ * sync we have to keep going because someone
+ * may be concurrently dirtying pages, and we
+ * might have synced a lot of newly appeared
+ * dirty pages, but have not synced all of the
+ * old dirty pages.
+ */
+ done = 1;
+ break;
}
+
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
done = 1;