linux-kernel - Re: [PATCH bpf-next] bpf: cap BPF_PROG_PACK_SIZE to 2MB * num_possible

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Date: Fri, 8 Mar 2024 15:08:15 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Song Liu <song@...nel.org>
Cc: Puranjay Mohan <puranjay12@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yonghong.song@...ux.dev>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: cap BPF_PROG_PACK_SIZE to 2MB * num_possible_nodes()

On Fri, Mar 8, 2024 at 8:55 AM Song Liu <song@...nel.org> wrote:
>
> On Fri, Mar 8, 2024 at 4:07 AM Puranjay Mohan <puranjay12@...il.com> wrote:
> >
> > On some architectures like ARM64, PMD_SIZE can be really large in some
> > configurations. Like with CONFIG_ARM64_64K_PAGES=y the PMD_SIZE is
> > 512MB.
> >
> > Use 2MB * num_possible_nodes() as the upper limit for allocations done
> > through the prog pack allocator.
> >
> > Fixes: ea2babac63d4 ("bpf: Simplify bpf_prog_pack_[size|mask]")
> > Reported-by: "kernelci.org bot" <bot@...nelci.org>
> > Closes: https://lore.kernel.org/all/7e216c88-77ee-47b8-becc-a0f780868d3c@sirena.org.uk/
> > Suggested-by: Song Liu <song@...nel.org>
> > Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
> > ---
> >  kernel/bpf/core.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index 134b7979f537..83a3b6964e54 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -893,8 +893,17 @@ static LIST_HEAD(pack_list);
> >   * CONFIG_MMU=n. Use PAGE_SIZE in these cases.
> >   */
> >  #ifdef PMD_SIZE
> > +/*
> > + * PMD_SIZE is really big for some archs. It doesn't make sense to
> > + * reserve too much memory in one allocation. Cap BPF_PROG_PACK_SIZE to
> > + * 2MiB * num_possible_nodes().
> > + */
>
> In BPF code, we prefer a different style of multiple line comments:
>
> /* PMD_SIZE is really big for some archs. It doesn't make sense to
>  * reserve too much memory in one allocation. Cap BPF_PROG_PACK_SIZE to
>  * 2MiB * num_possible_nodes().
>  */

Fixed up while applying. Thanks everyone.