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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Mon, 11 Mar 2024 19:13:05 -0700
Message-ID: <CAADnVQKsrLB-2bD53R4ZdzUVdx1aqkgom1rzGCGKK0M3Uc+csQ@mail.gmail.com>
Subject: Re: [External] Re: [PATCH bpf-next v2 7/9] libbpf: don't free btf if
 program of multi-link tracing existing
To: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, Martin KaFai Lau <martin.lau@linux.dev>, Eddy Z <eddyz87@gmail.com>, 
	Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, 
	John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Alexander Gordeev <agordeev@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, 
	Sven Schnelle <svens@linux.ibm.com>, "David S. Miller" <davem@davemloft.net>, 
	David Ahern <dsahern@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, 
	X86 ML <x86@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Quentin Monnet <quentin@isovalent.com>, 
	bpf <bpf@vger.kernel.org>, 
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On Mon, Mar 11, 2024 at 7:05=E2=80=AFPM =E6=A2=A6=E9=BE=99=E8=91=A3 <dongme=
nglong.8@bytedance.com> wrote:
>
> > >
> > > +LIBBPF_API void bpf_object__free_btfs(struct bpf_object *obj);
> > > +
> >
> > It shouldn't be exported.
> > libbpf should clean it up when bpf_object is freed.
>
> Yes, libbpf will clean up the btfs when bpf_object is freed in
> this commit. And I'm trying to offer a way to early free the btfs
> by the users manual to reduce the memory usage. Or, the
> btfs that we opened will keep existing until we close the
> bpf_object.
>
> This is optional, I can remove it if you prefer.

Let's not extend libbpf api unless we really need to.
bpf_program__attach_trace_multi_opts() and
*skel*__attach() can probably free them.
I don't see a use case where you'd want to keep them afterwards.