Re: [patch 1/3] mm: memcontrol: lockless page counters

Johannes Weiner
2014-10-08T12:31:50Z

On Tue, Oct 07, 2014 at 05:15:43PM +0200, Michal Hocko wrote:
> On Wed 24-09-14 11:43:08, Johannes Weiner wrote:
> > @@ -1490,12 +1495,23 @@ int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
> > */
> > static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
> > {
> > - unsigned long long margin;
> > + unsigned long margin = 0;
> > + unsigned long count;
> > + unsigned long limit;
> >
> > - margin = res_counter_margin(&memcg->res);
> > - if (do_swap_account)
> > - margin = min(margin, res_counter_margin(&memcg->memsw));
> > - return margin >> PAGE_SHIFT;
> > + count = page_counter_read(&memcg->memory);
> > + limit = ACCESS_ONCE(memcg->memory.limit);
> > + if (count < limit)
> > + margin = limit - count;
> > +
> > + if (do_swap_account) {
> > + count = page_counter_read(&memcg->memsw);
> > + limit = ACCESS_ONCE(memcg->memsw.limit);
> > + if (count < limit)
>
> I guess you wanted (count <= limit) here?

Yes. Fixed it up, thanks.

> > @@ -2293,33 +2295,31 @@ static DEFINE_MUTEX(percpu_charge_mutex);
> > static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
> > {
> > struct memcg_stock_pcp *stock;
> > - bool ret = true;
> > + bool ret = false;
> >
> > if (nr_pages > CHARGE_BATCH)
> > - return false;
> > + return ret;
> >
> > stock = &get_cpu_var(memcg_stock);
> > - if (memcg == stock->cached && stock->nr_pages >= nr_pages)
> > + if (memcg == stock->cached && stock->nr_pages >= nr_pages) {
> > stock->nr_pages -= nr_pages;
> > - else /* need to call res_counter_charge */
> > - ret = false;
> > + ret = true;
> > + }
> > put_cpu_var(memcg_stock);
> > return ret;
>
> This change is not really needed but at least it woke me up after some
> monotonic and mechanical changes...

This hunk started with removing the res_counter_charge comment. IIRC,
Andrew advocated minor cleanups in the area in the past, so I figured
I make the thing a bit more readable while I'm there anyway.