Re: [PATCH] writeback: sum memcg dirty counters as needed

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Mar 27, 2019 at 03:29:47PM -0700, Greg Thelen wrote:
> On Fri, Mar 22, 2019 at 11:15 AM Roman Gushchin <guro@fb.com> wrote:
> > On Thu, Mar 07, 2019 at 08:56:32AM -0800, Greg Thelen wrote:
> > > +     int cpu;
> > > +
> > > +     for_each_online_cpu(cpu)
> > > +             x += per_cpu_ptr(memcg->stat_cpu, cpu)->count[idx];
> > > +     if (x < 0)
> > > +             x = 0;
> > > +#endif
> > > +     return x;
> > > +}
> >
> > Also, isn't it worth it to generalize memcg_page_state() instead?
> > By adding an bool exact argument? I believe dirty balance is not
> > the only place, where we need a better accuracy.
> 
> Nod.  I'll provide a more general version of memcg_page_state().  I'm
> testing updated (forthcoming v2) patch set now with feedback from
> Andrew and Roman.

I'm working on a patch series that reworks the memcg_page_state() API
and by far the most callers do NOT need the exact numbers. So I'd ask
to please keep this a separate function so I don't have to update tens
of callsites to pass "false". Thanks!