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| author | Wu Fengguang <fengguang.wu@intel.com> | 2011-08-04 22:16:46 -0600 |
|---|---|---|
| committer | Wu Fengguang <fengguang.wu@intel.com> | 2011-10-03 21:08:58 +0800 |
| commit | 8927f66c4ede9a18b4b58f7e6f9debca67065f6b (patch) | |
| tree | f7c8490ab23a20cb86874ca8112f3dd1fc6002ae /mm/page-writeback.c | |
| parent | 57fc978cfb61ed40a7bbfe5a569359159ba31abd (diff) | |
| download | lwn-8927f66c4ede9a18b4b58f7e6f9debca67065f6b.tar.gz lwn-8927f66c4ede9a18b4b58f7e6f9debca67065f6b.zip | |
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>
Diffstat (limited to 'mm/page-writeback.c')
| -rw-r--r-- | mm/page-writeback.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 6a8bb693b429..325f753c80ed 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -599,6 +599,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, */ if (unlikely(bdi_thresh > thresh)) bdi_thresh = thresh; + bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); /* * scale global setpoint to bdi's: * bdi_setpoint = setpoint * bdi_thresh / thresh @@ -622,6 +623,20 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, } else pos_ratio /= 4; + /* + * bdi reserve area, safeguard against dirty pool underrun and disk idle + * It may push the desired control point of global dirty pages higher + * than setpoint. + */ + x_intercept = bdi_thresh / 2; + if (bdi_dirty < x_intercept) { + if (bdi_dirty > x_intercept / 8) { + pos_ratio *= x_intercept; + do_div(pos_ratio, bdi_dirty); + } else + pos_ratio *= 8; + } + return pos_ratio; } |