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Date: Wed, 15 May 2024 15:43:26 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
Cc: Jesper Dangaard Brouer <hawk@kernel.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Boqun Feng <boqun.feng@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Eric Dumazet <edumazet@google.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Jakub Kicinski <kuba@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <longman@redhat.com>, Will Deacon <will@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Eduard Zingerman <eddyz87@gmail.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>, Song Liu <song@kernel.org>,
	Stanislav Fomichev <sdf@google.com>,
	Yonghong Song <yonghong.song@linux.dev>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH net-next 14/15 v2] net: Reference bpf_redirect_info via
 task_struct on PREEMPT_RT.
Message-ID: <20240515134326.14x755Wb@linutronix.de>
References: <20240503182957.1042122-1-bigeasy@linutronix.de>
 <20240503182957.1042122-15-bigeasy@linutronix.de>
 <87y18mohhp.fsf@toke.dk>
 <CAADnVQJkiwaYXUo+LyKoV96VFFCFL0VY5Jgpuv_0oypksrnciA@mail.gmail.com>
 <20240507123636.cTnT7TvU@linutronix.de>
 <93062ce7-8dfa-48a9-a4ad-24c5a3993b41@kernel.org>
 <20240510162121.f-tvqcyf@linutronix.de>
 <87le4cd2ws.fsf@toke.dk>
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In-Reply-To: <87le4cd2ws.fsf@toke.dk>

On 2024-05-14 13:54:43 [+0200], Toke H=C3=B8iland-J=C3=B8rgensen wrote:
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1504,6 +1505,8 @@ struct task_struct {
> >  	/* Used for BPF run context */
> >  	struct bpf_run_ctx		*bpf_ctx;
> >  #endif
> > +	/* Used by BPF for per-TASK xdp storage */
> > +	struct bpf_net_context		*bpf_net_context;
>=20
> Okay, so if we are going the route of always putting this in 'current',
> why not just embed the whole struct bpf_net_context inside task_struct,
> instead of mucking about with the stack-allocated structures and
> setting/clearing of pointers?

The whole struct bpf_net_context has 112 bytes. task_struct has 12352
bytes in my debug-config or 7296 bytes with defconfig on x86-64. Adding
it unconditionally would grow task_struct by ~1% but it would make
things way easier: The NULL case goes away, the assignment and cleanup
goes away, the INIT_LIST_HEAD can be moved to fork(). If the size
increase is not an issue then why not. Let me prepare=E2=80=A6

> -Toke

Sebastian