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writeback: set max_pause to lowest value on zero bdi_dirty

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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>
This commit is contained in:
Wu Fengguang 2011-12-02 18:21:51 -06:00
parent c5c6343c4d
commit 82e230a07d
1 changed files with 1 additions and 2 deletions
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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).