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 <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Proposed-by: Con Kolivas <kernel@kolivas.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Rubin <mrubin@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4dd91f7..b840afa 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -415,14 +415,8 @@
if (vm_dirty_bytes)
dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
- else {
- int dirty_ratio;
-
- dirty_ratio = vm_dirty_ratio;
- if (dirty_ratio < 5)
- dirty_ratio = 5;
- dirty = (dirty_ratio * available_memory) / 100;
- }
+ else
+ dirty = (vm_dirty_ratio * available_memory) / 100;
if (dirty_background_bytes)
background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
@@ -510,7 +504,7 @@
* catch-up. This avoids (excessively) small writeouts
* when the bdi limits are ramping up.
*/
- if (nr_reclaimable + nr_writeback <
+ if (nr_reclaimable + nr_writeback <=
(background_thresh + dirty_thresh) / 2)
break;
@@ -542,8 +536,8 @@
* the last resort safeguard.
*/
dirty_exceeded =
- (bdi_nr_reclaimable + bdi_nr_writeback >= bdi_thresh)
- || (nr_reclaimable + nr_writeback >= dirty_thresh);
+ (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
+ || (nr_reclaimable + nr_writeback > dirty_thresh);
if (!dirty_exceeded)
break;