Messages in this thread Patch in this message | | | Subject | Re: bdi_min_ratio never shrinks, ultimately preventing valid setting of min_ratio | From | Peter Zijlstra <> | Date | Thu, 02 Jun 2011 23:25:58 +0200 |
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On Thu, 2011-06-02 at 13:32 -0500, lkml@pengaru.com wrote: > > > There is no place in this listing where the value is decremented by the > > > respective bdi's min_ratio when a bdi is torn down. > > > > There is, adding a negative number is equal to a subtraction. > > > > min_ratio -= bdi->min_ratio; > > if (bdi_min_ratio + min_ratio < 100) { > > bdi_min_ratio += min_ratio; > > bdi->min_ratio += min_ratio; > > } > > > > is the relevant piece, note that bdi->min_ratio is the current setting, > > this makes min_ratio the difference between the new and old setting, and > > adding this to both bdi_min_ratio (the global sum) and bdi->min_ratio > > dtrt regardless if the new value is larger or smaller than the old > > value. > > This accounts for the repeated setting of min_ratio on the same bdi. But > does bdi_set_min_ratio() get entered with a min_ratio of 0 on bdi removal? > If not, we leak the non-zero min_ratio of a removed bdi.
That does not appear to be the case, good catch. Would you be bitten by that particular scenario? If so, does the below cure things for you?
--- mm/backing-dev.c | 1 + 1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index f032e6e..e56fe35 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -606,6 +606,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi) void bdi_unregister(struct backing_dev_info *bdi) { if (bdi->dev) { + bdi_set_min_ratio(bdi, 0); trace_writeback_bdi_unregister(bdi); bdi_prune_sb(bdi); del_timer_sync(&bdi->wb.wakeup_timer);
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