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SubjectRe: bdi_min_ratio never shrinks, ultimately preventing valid setting of min_ratio
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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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