Re: [PATCH 2/5] writeback: dirty position control

[Wu Fengguang]

> > > > +	x_intercept = setpoint + 2 * span;
>    ^^ BTW, why do you have 2*span here? It can result in x_intercept being
> ~3*bdi_thresh... So maybe you should use bdi_thresh/2 in the computation of
> span?

OK, I'll follow your suggestion to use

        span = 8 * write_bw, for single bdi case 
        span = bdi_thresh, for JBOD case
        x_intercept = setpoint + span;

It does make sense to squeeze the bdi_dirty fluctuation range a bit by
doubling span and making the control line more sharp.

Thanks,
Fengguang
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