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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@ -989,8 +989,7 @@ static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
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*
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* 8 serves as the safety ratio.
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*/
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if (bdi_dirty)
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t = min(t, bdi_dirty * HZ / (8 * bw + 1));
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t = min(t, bdi_dirty * HZ / (8 * bw + 1));
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/*
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* The pause time will be settled within range (max_pause/4, max_pause).
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