linux-kernel - Re: [PATCH] mm/mempolicy: failed to disable numa balancing

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Message-ID: <CAOUHufZaL2S6Aa1ey3Mk+h+bGr2Tbg_LxOkjbuj87psukPe-gQ@mail.gmail.com>
Date:   Sun, 4 Dec 2022 15:58:46 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     tzm <tcm1030@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH] mm/mempolicy: failed to disable numa balancing

On Fri, Dec 2, 2022 at 1:00 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri,  2 Dec 2022 22:16:30 +0800 tzm <tcm1030@....com> wrote:
>
> > It will be failed to  disable numa balancing policy permanently by passing
> > <numa_balancing=disable> to boot cmdline parameters.
> > The numabalancing_override variable is int and 1 for enable -1 for disable.
> > So, !enumabalancing_override will always be true, which cause this bug.

!enumabalancing_override is false when enumabalancing_override = -1
(numa_balancing=disable).

> That's really old code!
>
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2865,7 +2865,7 @@ static void __init check_numabalancing_enable(void)
> >       if (numabalancing_override)
> >               set_numabalancing_state(numabalancing_override == 1);
> >
> > -     if (num_online_nodes() > 1 && !numabalancing_override) {
> > +     if (num_online_nodes() > 1 && (numabalancing_override == 1)) {
> >               pr_info("%s automatic NUMA balancing. Configure with numa_balancing= or the kernel.numa_balancing sysctl\n",
> >                       numabalancing_default ? "Enabling" : "Disabling");
> >               set_numabalancing_state(numabalancing_default);
>
> Looks right to me.  Mel?
>
> After eight years, I wonder if we actually need this.

NAK.

The original code works as intended. This patch breaks my test with
CONFIG_NUMA_BALANCING_DEFAULT_ENABLED=n and numa_balancing=enable.