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Date:   Fri, 25 Feb 2022 15:43:29 -0500
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Subject: Re: [PATCH bpf-next v2] bpf: Cache the last valid build_id.
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To:     Hao Luo <haoluo@google.com>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Cc:     Song Liu <songliubraving@fb.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Blake Jones <blakejones@google.com>, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, Greg Thelen <gthelen@google.com>
References: <20220224000531.1265030-1-haoluo@google.com>
From:   Pasha Tatashin <pasha.tatashin@soleen.com>
In-Reply-To: <20220224000531.1265030-1-haoluo@google.com>
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On 2/23/22 19:05, Hao Luo 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>

Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>

Thanks,
Pasha