On Fri 04-02-11 14:09:16, Peter Zijlstra wrote:
> On Fri, 2011-02-04 at 02:38 +0100, Jan Kara wrote:
> > +static int check_dirty_limits(struct backing_dev_info *bdi,
> > + struct dirty_limit_state *pst)
> > +{
> > + struct dirty_limit_state st;
> > + unsigned long bdi_thresh;
> > + unsigned long min_bdi_thresh;
> > + int ret = DIRTY_OK;
> >
> > + get_global_dirty_limit_state(&st);
> > + /*
> > + * Throttle it only when the background writeback cannot catch-up. This
> > + * avoids (excessively) small writeouts when the bdi limits are ramping
> > + * up.
> > + */
> > + if (st.nr_reclaimable + st.nr_writeback <=
> > + (st.background_thresh + st.dirty_thresh) / 2)
> > + goto out;
> >
> > + get_bdi_dirty_limit_state(bdi, &st);
> > + min_bdi_thresh = task_min_dirty_limit(st.bdi_thresh);
> > + bdi_thresh = task_dirty_limit(current, st.bdi_thresh);
> > +
> > + /*
> > + * The bdi thresh is somehow "soft" limit derived from the global
> > + * "hard" limit. The former helps to prevent heavy IO bdi or process
> > + * from holding back light ones; The latter is the last resort
> > + * safeguard.
> > + */
> > + if ((st.bdi_nr_reclaimable + st.bdi_nr_writeback > bdi_thresh)
> > + || (st.nr_reclaimable + st.nr_writeback > st.dirty_thresh)) {
> > + ret = DIRTY_EXCEED_LIMIT;
> > + goto out;
> > + }
> > + if (st.bdi_nr_reclaimable + st.bdi_nr_writeback > min_bdi_thresh) {
> > + ret = DIRTY_MAY_EXCEED_LIMIT;
> > + goto out;
> > + }
> > + if (st.nr_reclaimable > st.background_thresh)
> > + ret = DIRTY_EXCEED_BACKGROUND;
> > +out:
> > + if (pst)
> > + *pst = st;
>
> By mandating pst is always provided you can reduce the total stack
> footprint, avoid the memcopy and clean up the control flow ;-)
OK, will do.
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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