tree f7c8490ab23a20cb86874ca8112f3dd1fc6002ae
parent 57fc978cfb61ed40a7bbfe5a569359159ba31abd
author Wu Fengguang <fengguang.wu@intel.com> 1312517806 -0600
committer Wu Fengguang <fengguang.wu@intel.com> 1317647338 +0800

writeback: dirty position control - bdi reserve area

Keep a minimal pool of dirty pages for each bdi, so that the disk IO
queues won't underrun. Also gently increase a small bdi_thresh to avoid
it stuck in 0 for some light dirtied bdi.

It's particularly useful for JBOD and small memory system.

It may result in (pos_ratio > 1) at the setpoint and push the dirty
pages high. This is more or less intended because the bdi is in the
danger of IO queue underflow.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>