netdev - Re: [PATCH bpf-next v9 05/11] bpf: support fsession for bpf_session

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Message-ID: <CAADnVQJzkXysOO9jqdvJUYbe2t+urReRV2xWQ0L2z0qcjgxdcw@mail.gmail.com>
Date: Tue, 13 Jan 2026 18:33:07 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Menglong Dong <menglong8.dong@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, jiang.biao@...ux.dev, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, 
	"H. Peter Anvin" <hpa@...or.com>, bpf <bpf@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v9 05/11] bpf: support fsession for bpf_session_cookie

On Tue, Jan 13, 2026 at 5:24 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Sat, Jan 10, 2026 at 6:12 AM Menglong Dong <menglong8.dong@...il.com> wrote:
> >
> > Implement session cookie for fsession. In order to limit the stack usage,
> > we make 4 as the maximum of the cookie count.
>
> This 4 is so random, tbh. Do we need to artificially limit it? Even if
> all BPF_MAX_TRAMP_LINKS = 38 where using session cookies, it would be
> 304 bytes. Not insignificant, but also not world-ending and IMO so
> unlikely that I wouldn't add extra limits at all.

I forgot that we already have BPF_MAX_TRAMP_LINKS limit for the total
number of progs. I guess extra 8 bytes per fsession prog isn't that bad.