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References: <20220224000531.1265030-1-haoluo@google.com>
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From:   Song Liu <song@kernel.org>
Date:   Wed, 23 Feb 2022 18:31:15 -0800
Message-ID: <CAPhsuW6BqEn8azap_zcWq0Zkvv8mRFg6g0UX2fPQXwzT+F6V=A@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2] bpf: Cache the last valid build_id.
To:     Hao Luo <haoluo@google.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Song Liu <songliubraving@fb.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Blake Jones <blakejones@google.com>, bpf <bpf@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Greg Thelen <gthelen@google.com>
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On Wed, Feb 23, 2022 at 4:05 PM Hao Luo <haoluo@google.com> wrote:
>
> For binaries that are statically linked, consecutive stack frames are
> likely to be in the same VMA and therefore have the same build id.
> As an optimization for this case, we can cache the previous frame's
> VMA, if the new frame has the same VMA as the previous one, reuse the
> previous one's build id. We are holding the MM locks as reader across
> the entire loop, so we don't need to worry about VMA going away.
>
> Tested through "stacktrace_build_id" and "stacktrace_build_id_nmi" in
> test_progs.
>
> Suggested-by: Greg Thelen <gthelen@google.com>
> Signed-off-by: Hao Luo <haoluo@google.com>

Nice optimization!

Acked-by: Song Liu <songliubraving@fb.com>