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From:   Shakeel Butt <shakeelb@google.com>
Date:   Thu, 25 Aug 2022 08:24:02 -0700
Message-ID: <CALvZod6tFce5Ld9rh-xt495S+A-vi4Curkja2YYyf0VizKw1tw@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] mm: page_counter: rearrange struct page_counter fields
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <songmuchun@bytedance.com>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Eric Dumazet <edumazet@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        Feng Tang <feng.tang@intel.com>,
        Oliver Sang <oliver.sang@intel.com>, lkp@lists.01.org,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        netdev <netdev@vger.kernel.org>,
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On Wed, Aug 24, 2022 at 10:21 PM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Wed, 24 Aug 2022 21:41:42 -0700 Shakeel Butt <shakeelb@google.com> wrote:
>
> > > Did you evaluate the effects of using a per-cpu counter of some form?
> >
> > Do you mean per-cpu counter for usage or something else?
>
> percpu_counter, perhaps.  Or some hand-rolled thing if that's more suitable.
>
> > The usage
> > needs to be compared against the limits and accumulating per-cpu is
> > costly particularly on larger machines,
>
> Well, there are tricks one can play.  For example, only run
> __percpu_counter_sum() when `usage' is close to its limit.
>
> I'd suggest flinging together a prototype which simply uses
> percpu_counter_read() all the time.  If the performance testing results
> are sufficiently promising, then look into the accuracy issues.
>

Thanks, I will take a stab at that in a week or so.