linux-kernel - Re: [PATCH v2 1/2] mm: memcg: refactor page state unit helpers

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Date:   Wed, 4 Oct 2023 09:58:46 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: memcg: refactor page state unit helpers

On Wed, Oct 4, 2023 at 2:02 AM Michal Koutný <mkoutny@...e.com> wrote:
>
> On Tue, Oct 03, 2023 at 12:47:25PM -0700, Yosry Ahmed <yosryahmed@...gle.com> wrote:
> > Those constants are shared with code outside of memcg, namely enum
> > node_stat_item and enum vm_event_item, and IIUC they are used
> > differently outside of memcg. Did I miss something?
>
> The difference is not big, e.g.
>   mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
> could be
>   __count_memcg_events(
>     container_of(lruvec, struct mem_cgroup_per_node, lruvec)->memcg,
>     WORKINGSET_ACTIVATE_BASE + type, delta
>   );
>
> Yes, it would mean transferring WORKINGSET_* items from enum
> node_stat_item to enum vm_event_item.
> IOW, I don't know what is the effective difference between
> mod_memcg_lruvec_state() and count_memcg_events().
> Is it per-memcg vs per-memcg-per-node resolution?
> (Is _that_ read by workingset mechanism?)

Even if it is not read, I think it is exposed in memory.numa_stat, right?

Outside of memcg code, if you look at vmstat_start(), you will see
that the items in enum vm_event_item are handled differently (see
all_vm_events()) when reading vmstat. I don't think we can just move
it, unfortunately.

>
> Thanks,
> Michal