linux-kernel - Re: [PATCH v3 4/8] memcg: reduce memory for the lruvec and memcg stats

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Date: Tue, 30 Apr 2024 16:00:42 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	"T . J . Mercier" <tjmercier@...gle.com>, kernel-team@...a.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/8] memcg: reduce memory for the lruvec and memcg
 stats

On Tue, Apr 30, 2024 at 10:41:01AM -0700, Yosry Ahmed wrote:
> On Tue, Apr 30, 2024 at 10:38 AM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> >
> > On Tue, Apr 30, 2024 at 01:41:38AM -0700, Yosry Ahmed wrote:
> > > On Mon, Apr 29, 2024 at 11:06 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> > > >
> > [...]
> > > > +
> > > > +#define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
> > > > +#define NR_MEMCG_STATS (NR_MEMCG_NODE_STAT_ITEMS + ARRAY_SIZE(memcg_stat_items))
> > > > +static int8_t mem_cgroup_stats_index[MEMCG_NR_STAT] __read_mostly;
> > >
> > > NR_MEMCG_STATS and MEMCG_NR_STAT are awfully close and have different
> > > meanings. I think we should come up with better names (sorry nothing
> > > 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 = 0;
> > > > +
> > > > +       /* Switch to short once this failure occurs. */
> > > > +       BUILD_BUG_ON(NR_MEMCG_STATS >= 127 /* INT8_MAX */);

The above should be MEMCG_NR_STAT instead of NR_MEMCG_STATS.