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writeback: set max_pause to lowest value on zero bdi_dirty

Some trace shows lots of bdi_dirty=0 lines where it's actually some
small value if w/o the accounting errors in the per-cpu bdi stats.

In this case the max pause time should really be set to the smallest
(non-zero) value to avoid IO queue underrun and improve throughput.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
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1 parent c5c6343 commit 82e230a07de3812a5e87a27979f033dad59172e3 @fengguang fengguang committed Dec 3, 2011
Showing with 1 addition and 2 deletions.
  1. +1 −2 mm/page-writeback.c
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@@ -989,8 +989,7 @@ static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
*
* 8 serves as the safety ratio.
*/
- if (bdi_dirty)
- t = min(t, bdi_dirty * HZ / (8 * bw + 1));
+ t = min(t, bdi_dirty * HZ / (8 * bw + 1));
/*
* The pause time will be settled within range (max_pause/4, max_pause).

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