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From: Yosry Ahmed <yosryahmed@google.com>
Date: Tue, 30 Apr 2024 16:07:05 -0700
Message-ID: <CAJD7tkbue8S86YZE3y_1qOF5ee14F9MCuh2iJ0BNBZC8QpL=_Q@mail.gmail.com>
Subject: Re: [PATCH v3 4/8] memcg: reduce memory for the lruvec and memcg stats
To: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, 
	Michal Hocko <mhocko@kernel.org>, Roman Gushchin <roman.gushchin@linux.dev>, 
	Muchun Song <muchun.song@linux.dev>, "T . J . Mercier" <tjmercier@google.com>, kernel-team@meta.com, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Tue, Apr 30, 2024 at 4:00=E2=80=AFPM Shakeel Butt <shakeel.butt@linux.de=
v> wrote:
>
> On Tue, Apr 30, 2024 at 10:41:01AM -0700, Yosry Ahmed wrote:
> > On Tue, Apr 30, 2024 at 10:38=E2=80=AFAM Shakeel Butt <shakeel.butt@lin=
ux.dev> wrote:
> > >
> > > On Tue, Apr 30, 2024 at 01:41:38AM -0700, Yosry Ahmed wrote:
> > > > On Mon, Apr 29, 2024 at 11:06=E2=80=AFPM Shakeel Butt <shakeel.butt=
@linux.dev> wrote:
> > > > >
> > > [...]
> > > > > +
> > > > > +#define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_item=
s)
> > > > > +#define NR_MEMCG_STATS (NR_MEMCG_NODE_STAT_ITEMS + ARRAY_SIZE(me=
mcg_stat_items))
> > > > > +static int8_t mem_cgroup_stats_index[MEMCG_NR_STAT] __read_mostl=
y;
> > > >
> > > > NR_MEMCG_STATS and MEMCG_NR_STAT are awfully close and have differe=
nt
> > > > meanings. I think we should come up with better names (sorry nothin=
g
> > > > comes to mind) or add a comment to make the difference more obvious=
.
> > > >
> > >
> > > How about the following comment?
> >
> > The comment LGTM. I prefer renaming them though if someone can come up
> > with better names.
> >
>
> I will be posting v4 and will change the name (still thinking about the
> name) becasuse:
>
> > > > > +static void init_memcg_stats(void)
> > > > > +{
> > > > > +       int8_t i, j =3D 0;
> > > > > +
> > > > > +       /* Switch to short once this failure occurs. */
> > > > > +       BUILD_BUG_ON(NR_MEMCG_STATS >=3D 127 /* INT8_MAX */);
>
> The above should be MEMCG_NR_STAT instead of NR_MEMCG_STATS.

Yeah it's pretty confusing :)

How about something explicit like:

NR_MEMCG_POSSIBLE_STAT_ITEMS / MEMCG_MAX_STAT_ITEM
NR_MEMCG_ACTUAL_STAT_ITEMS / MEMCG_ACTUAL_NR_STAT

They look ugly, but I can't think of anything better. Maybe they will
inspire something better :)