netdev - Re: [External] Re: [PATCH bpf-next v2 7/9] libbpf: don't free btf if program of multi-link tracing existing

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Message-ID: <CAADnVQKsrLB-2bD53R4ZdzUVdx1aqkgom1rzGCGKK0M3Uc+csQ@mail.gmail.com>
Date: Mon, 11 Mar 2024 19:13:05 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: 梦龙董 <dongmenglong.8@...edance.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <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@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Sven Schnelle <svens@...ux.ibm.com>, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	X86 ML <x86@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Quentin Monnet <quentin@...valent.com>, 
	bpf <bpf@...r.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-riscv <linux-riscv@...ts.infradead.org>, linux-s390 <linux-s390@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, linux-trace-kernel@...r.kernel.org, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [External] Re: [PATCH bpf-next v2 7/9] libbpf: don't free btf if
 program of multi-link tracing existing

On Mon, Mar 11, 2024 at 7:05 PM 梦龙董 <dongmenglong.8@...edance.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.