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    SubjectRe: [PATCH 4/4] writeback, memcg: Implement foreign dirty flushing
    Hello,

    On Tue, Aug 06, 2019 at 04:03:06PM -0700, Andrew Morton wrote:
    > > + if (i < MEMCG_CGWB_FRN_CNT) {
    > > + unsigned long update_intv =
    > > + min_t(unsigned long, HZ,
    > > + msecs_to_jiffies(dirty_expire_interval * 10) / 8);
    >
    > An explanation of what's going on here would be helpful.
    >
    > Why "* 1.25" and not, umm "* 1.24"?

    Just because /8 is cheaper. It's likely that a fairly wide range of
    numbers are okay for the above. I'll add some comment to explain that
    and why the specific constants are picked.

    > > +void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
    > > +{
    > > + struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
    > > + unsigned long intv = msecs_to_jiffies(dirty_expire_interval * 10);
    >
    > Ditto.

    This is just dirty expiration. If the dirty data has expired,
    writeback must already be in progress by its bdi_wb, so there's no
    reason to scheduler foreign writeback. Will add a comment.

    Thanks.

    --
    tejun

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