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Wu Fengguang authored
We do "floating proportions" to let active devices to grow its target share of dirty pages and stalled/inactive devices to decrease its target share over time. It works well except in the case of "an inactive disk suddenly goes busy", where the initial target share may be too small. To mitigate this, bdi_position_ratio() has the below line to raise a small bdi_thresh when it's safe to do so, so that the disk be feed with enough dirty pages for efficient IO and in turn fast rampup of bdi_thresh: bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); balance_dirty_pages() normally does negative feedback control which adjusts ratelimit to balance the bdi dirty pages around the target. In some extreme cases when that is not enough, it will have to block the tasks completely until the bdi dirty pages drop below bdi_thresh. Acked-by: Jan Kara <jack@suse.cz> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
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