> > The global threshold check is added in place of clip_bdi_dirty_limit()
> > for safety and not intended as a behavior change. If ever leading to
> > big behavior change and regression, that it would be indicating some
> > too permissive per-bdi threshold calculation.
> >
> > Did you see the global dirty threshold get exceeded when writing to 2+
> > devices? Occasional small exceeding should be OK though. I tried the
> > following debug patch and see no warnings when doing two concurrent cp
> > over local disk and NFS.
> Oops, sorry. I've misread the code. You're right. There shouldn't be a big
> change in the behavior.
It does indicate a missing point in the changelog. The paragraph is
updated to:
We now set and clear dirty_exceeded not only based on bdi dirty limits,
but also on the global dirty limit. The global limit check is added in
place of clip_bdi_dirty_limit() for safety and not intended as a
behavior change. The bdi limits should be tight enough to keep all dirty
pages under the global limit at most time; occasional small exceeding
should be OK though. The change makes the logic more obvious: the global
limit is the ultimate goal and shall be always imposed.
Thanks,
Fengguang
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