linux-kernel - Re: [PATCH] vmstat: don't auto expand the sysfs files

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Date:   Mon, 11 Dec 2023 12:09:57 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     gregkh@...uxfoundation.org, rafael@...nel.org,
        akpm@...ux-foundation.org, surenb@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        souravpanda@...gle.com
Subject: Re: [PATCH] vmstat: don't auto expand the sysfs files

On Mon, Dec 11, 2023 at 12:00 PM Matthew Wilcox <willy@...radead.org> 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 *dev,
> >       int i;
> >       int len = 0;
> >
> > -     for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
> > -             len += sysfs_emit_at(buf, len, "%s %lu\n",
> > -                                  zone_stat_name(i),
> > -                                  sum_zone_node_page_state(nid, i));
> > +     for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
> > +             if (vmstat_text[ZONE_STAT_NAME_IDX(i)].flags & VMSTAT_SHOW_SYSFS) {
> > +                     len += 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 = 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