linux-kernel - Re: [PATCH bpf-next v2 29/35] bpf: libbpf: cleanup RLIMIT

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Message-ID: <20200727231538.GA352883@carbon.DHCP.thefacebook.com>
Date:   Mon, 27 Jul 2020 16:15:38 -0700
From:   Roman Gushchin <guro@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     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 29/35] bpf: libbpf: cleanup RLIMIT_MEMLOCK
 usage

On Mon, Jul 27, 2020 at 03:05:11PM -0700, Andrii Nakryiko wrote:
> On Mon, Jul 27, 2020 at 12:21 PM Roman Gushchin <guro@...com> wrote:
> >
> > As bpf is not using memlock rlimit for memory accounting anymore,
> > let's remove the related code from libbpf.
> >
> > Bpf operations can't fail because of exceeding the limit anymore.
> >
> 
> They can't in the newest kernel, but libbpf will keep working and
> supporting old kernels for a very long time now. So please don't
> remove any of this.

Yeah, good point, agree.
So we just can drop this patch from the series, no other changes
are needed.

> 
> But it would be nice to add a detection of whether kernel needs a
> RLIMIT_MEMLOCK bump or not. Is there some simple and reliable way to
> detect this from user-space?

Hm, the best idea I can think of is to wait for -EPERM before bumping.
We can in theory look for the presence of memory.stat::percpu in cgroupfs,
but it's way to cryptic.

Thanks!