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

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Message-ID: <20190328140535.GA15622@cmpxchg.org>
Date:   Thu, 28 Mar 2019 10:05:35 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Greg Thelen <gthelen@...gle.com>
Cc:     Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Tejun Heo <tj@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] writeback: sum memcg dirty counters as needed

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@...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!