From: Eduard Zingerman <eddyz87@gmail.com>
To: wujing <realwujing@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>,
Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
Qiliang Yuan <yuanql9@chinatelecom.cn>
Subject: Re: [PATCH] bpf/verifier: compress bpf_reg_state by using bitfields
Date: Thu, 15 Jan 2026 10:55:30 -0800 [thread overview]
Message-ID: <7ffce4afdb0e859df7f0f87d170eda31b66a5b2b.camel@gmail.com> (raw)
In-Reply-To: <20260115152037.449362-1-realwujing@gmail.com>
On Thu, 2026-01-15 at 23:20 +0800, wujing wrote:
> The struct bpf_reg_state is 112 bytes long on 64-bit architectures,
> with several fields that have limited ranges. In particular, the bool
> 'precise' at the end causes 7 bytes of padding.
>
> This patch packs 'frameno', 'subreg_def', and 'precise' into a single
> u32/s32 bitfield block:
> - frameno: 4 bits (sufficient for MAX_CALL_FRAMES=8)
> - subreg_def: 27 bits (sufficient for 1M insns limit)
> - precise: 1 bit
>
> This reduces the size of struct bpf_reg_state from 112 to 104 bytes,
> saving 8 bytes per register. This also reduces the size of
> struct bpf_stack_state. Overall, it reduces peak memory usage of the
> verifier for complex programs with millions of states.
>
> The patch also updates states_maybe_looping() to use a non-bitfield
> boundary for memcmp(), as offsetof() cannot be used on bitfields.
>
> Signed-off-by: wujing <realwujing@gmail.com>
> Signed-off-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
> ---
varistat collects verifier memory usage statistics.
Does this change has an impact on programs generated for
e.g. selftests and sched_ext?
In general, you posted 4 patches claiming performance improvements,
but non of them are supported by any measurements.
P.S.
Is this LLM-generated?
next prev parent reply other threads:[~2026-01-15 18:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-15 15:20 [PATCH] bpf/verifier: compress bpf_reg_state by using bitfields wujing
2026-01-15 18:55 ` Eduard Zingerman [this message]
2026-01-16 6:07 ` Qiliang Yuan
2026-01-16 6:51 ` Eduard Zingerman
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