linux-kernel - Re: [PATCH bpf-next v2 27/35] bpf: eliminate rlimit-based memory accounting infra for bpf maps

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Date:   Mon, 27 Jul 2020 23:06:42 -0700
From:   Song Liu <song@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Roman Gushchin <guro@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 27/35] bpf: eliminate rlimit-based memory
 accounting infra for bpf maps

On Mon, Jul 27, 2020 at 10:58 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Mon, Jul 27, 2020 at 10:47 PM Song Liu <song@...nel.org> wrote:
> >
> > On Mon, Jul 27, 2020 at 12:26 PM Roman Gushchin <guro@...com> wrote:
> > >
> > > Remove rlimit-based accounting infrastructure code, which is not used
> > > anymore.
> > >
> > > Signed-off-by: Roman Gushchin <guro@...com>
> > [...]
> > >
> > >  static void bpf_map_put_uref(struct bpf_map *map)
> > > @@ -541,7 +484,7 @@ static void bpf_map_show_fdinfo(struct seq_file *m, struct file *filp)
> > >                    "value_size:\t%u\n"
> > >                    "max_entries:\t%u\n"
> > >                    "map_flags:\t%#x\n"
> > > -                  "memlock:\t%llu\n"
> > > +                  "memlock:\t%llu\n" /* deprecated */
> >
> > I am not sure whether we can deprecate this one.. How difficult is it
> > to keep this statistics?
> >
>
> It's factually correct now, that BPF map doesn't use any memlock memory, no?

I am not sure whether memlock really means memlock for all users... I bet there
are users who use memlock to check total memory used by the map.

>
> This is actually one way to detect whether RLIMIT_MEMLOCK is necessary
> or not: create a small map, check if it's fdinfo has memlock: 0 or not
> :)

If we do show memlock=0, this is a good check...

Thanks,
Song