Hello,
On Mon, Feb 08, 2021 at 03:29:21PM -0500, Johannes Weiner wrote:
> > > @@ -789,6 +793,7 @@ static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
> > > u64_stats_update_end(&blkg->iostat.sync);
> > >
> > > /* propagate global delta to parent */
> > > + /* XXX: could skip this if parent is root */
> > > if (parent) {
> > > u64_stats_update_begin(&parent->iostat.sync);
> > > blkg_iostat_set(&delta, &blkg->iostat.cur);
> >
> > Might as well update this similar to cgroup_base_stat_flush()?
>
> I meant to revisit that, but I'm never 100% confident when it comes to
> the interaction and lifetime of css, blkcg and blkg_gq.
Yeah, it does get hairy.
> IIUC, the blkg_gq->parent linkage always matches the css parent
> linkage; it just exists as an optimization for ancestor walks, which
> would otherwise have to do radix lookups when going through the css.
But yes, at least this part is straight-forward.
> So with the cgroup_parent() check at the beginning of the function
> making sure we're looking at a non-root group, blkg_gq->parent should
> also never be NULL and I can do if (paren->parent) directly, right?
I think so.
> > > static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
> > > {
> > > - struct cgroup *parent = cgroup_parent(cgrp);
> > > struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
> > > + struct cgroup *parent = cgroup_parent(cgrp);
> >
> > Is this chunk intentional?
>
> Yeah, it puts the local variable declarations into reverse christmas
> tree ordering to make them a bit easier to read. It's a while-at-it
> cleanup, mostly a force of habit. I can drop it if it bothers you.
I don't mind either way. Was just wondering whether it was accidental.
Thanks.
--
tejun
