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From:   Pasha Tatashin <pasha.tatashin@soleen.com>
Date:   Mon, 11 Dec 2023 12:09:57 -0500
Message-ID: <CA+CK2bBnPc=Z4SOPbnMqnDA1X9oLsq_rzsEnAcxNsA5ZWCUWwQ@mail.gmail.com>
Subject: Re: [PATCH] vmstat: don't auto expand the sysfs files
To:     Matthew Wilcox <willy@infradead.org>
Cc:     gregkh@linuxfoundation.org, rafael@kernel.org,
        akpm@linux-foundation.org, surenb@google.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        souravpanda@google.com
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On Mon, Dec 11, 2023 at 12:00=E2=80=AFPM Matthew Wilcox <willy@infradead.or=
g> wrote:
>
> On Mon, Dec 11, 2023 at 03:46:44PM +0000, Pasha Tatashin wrote:
> > +++ b/drivers/base/node.c
> > @@ -520,26 +520,34 @@ static ssize_t node_read_vmstat(struct device *de=
v,
> >       int i;
> >       int len =3D 0;
> >
> > -     for (i =3D 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
> > -             len +=3D sysfs_emit_at(buf, len, "%s %lu\n",
> > -                                  zone_stat_name(i),
> > -                                  sum_zone_node_page_state(nid, i));
> > +     for (i =3D 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
> > +             if (vmstat_text[ZONE_STAT_NAME_IDX(i)].flags & VMSTAT_SHO=
W_SYSFS) {
> > +                     len +=3D sysfs_emit_at(buf, len, "%s %lu\n",
> > +                                          zone_stat_name(i),
> > +                                          sum_zone_node_page_state(nid=
, i));
> > +             }
> > +     }
>
> This seems overly complicated.  Why not do:
>
>         for (i =3D 0; i < NR_VM_ZONE_STAT_SYSFS_ITEMS; i++)
>
> and have assertions that this number doesn't change (and require people
> to add to the list after that point)?

This is what I wanted to do at the beginning. But, the problem is that
vmstat_text[] contains names from a number of different structs of
stats:  zone_stat, numa_stat, node_stat, lru_list, writeback_stat,
vm_even. Therefore, we can't simply count the number of
NR_VM_ZONE_STAT_SYSFS_ITEMS, as the new items can be added in the
middle of vmstat_text[]  when for example numa_stat is expanded.

Pasha