writeback: remove the internal 5% low bound on dirty_ratio

The dirty_ratio was silently limited in global_dirty_limits() to >= 5%.
This is not a user expected behavior.  And it's inconsistent with
calc_period_shift(), which uses the plain vm_dirty_ratio value.

Let's remove the internal bound.

At the same time, fix balance_dirty_pages() to work with the
dirty_thresh=0 case.  This allows applications to proceed when
dirty+writeback pages are all cleaned.

And ">" fits with the name "exceeded" better than ">=" does.  Neil thinks
it is an aesthetic improvement as well as a functional one :)

Signed-off-by: Wu Fengguang <[email protected]>
Cc: Jan Kara <[email protected]>
Proposed-by: Con Kolivas <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Reviewed-by: Neil Brown <[email protected]>
Reviewed-by: KOSAKI Motohiro <[email protected]>
Cc: Michael Rubin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ab38fef1c9a1..97d2951bd4d1 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -582,7 +582,7 @@ static inline bool over_bground_thresh(void)
 	global_dirty_limits(&background_thresh, &dirty_thresh);
 
 	return (global_page_state(NR_FILE_DIRTY) +
-		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
+		global_page_state(NR_UNSTABLE_NFS) > background_thresh);
 }
 
 /*