Re: [PATCH v2 2/3] mm: page_counter: rearrange struct page_counter fields

From: Shakeel Butt <shakeelb@google.com>
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>,
	"Michal Koutný" <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>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/3] mm: page_counter: rearrange struct page_counter fields
Date: Thu, 25 Aug 2022 08:24:02 -0700	[thread overview]
Message-ID: <CALvZod6tFce5Ld9rh-xt495S+A-vi4Curkja2YYyf0VizKw1tw@mail.gmail.com> (raw)
In-Reply-To: <20220824222150.61c516a83bfe0ecb6c9b5348@linux-foundation.org>

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.