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 ;-)
> + return ret;
> +}
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