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[192.26.29.3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499820f5d26sm23033735e9.1.2026.08.12.21.38.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Aug 2026 21:38:54 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 13 Aug 2026 06:38:54 +0200 Message-Id: Cc: "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , , , , , Subject: Re: [PATCH] selftests/bpf: Remove duplicate copies of the arena spinlock qnodes From: "Kumar Kartikeya Dwivedi" To: "Changwoo Min" , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Shuah Khan" , "Emil Tsalapatis" X-Mailer: aerc 0.21.0 References: <20260803001807.646357-1-changwoo@igalia.com> In-Reply-To: <20260803001807.646357-1-changwoo@igalia.com> On Mon Aug 3, 2026 at 2:18 AM CEST, Changwoo Min wrote: > bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so > every translation unit including it emits a copy. __weak makes them all > resolve to one instance, but bpftool gen object merges only the symbols > and concatenates each input's .addr_space.1 bytes, leaving the surplus > copies unreferenced in the linked object. > > libarena links ten such units, so nine copies were dead weight (bytes): > > object before after > ----------------------------------------------------- > .addr_space.1 in libarena.bpf.o 676200 86376 > libarena.skel.h 2100123 892371 > libarena_asan.skel.h 2641124 1466477 > > Declare qnodes in the header and let each program define it once: > libarena in src/common.bpf.c, and the arena_spin_lock test beside the > lock it guards. > > Tested with test_progs -t arena_spin_lock and -t libarena. > > Signed-off-by: Changwoo Min > --- This seems ok to me. I don't have better ideas. Emil, any thoughts? > .../selftests/bpf/libarena/include/bpf_arena_spin_lock.h | 7 +------ > tools/testing/selftests/bpf/libarena/src/common.bpf.c | 7 +++++++ > tools/testing/selftests/bpf/progs/arena_spin_lock.c | 7 +++++++ > 3 files changed, 15 insertions(+), 6 deletions(-) > > diff --git a/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_= lock.h b/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h > index ae6b72d15bb6..71d9db610263 100644 > --- a/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h > +++ b/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h > @@ -103,12 +103,7 @@ struct arena_qnode { > #define _Q_LOCKED_VAL (1U << _Q_LOCKED_OFFSET) > #define _Q_PENDING_VAL (1U << _Q_PENDING_OFFSET) > > -/* > - * The qnodes are marked __weak so we can define them in the header > - * while still ensuring all compilation units use the same struct > - * instance. > - */ > -struct arena_qnode __weak __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NO= DES]; > +extern struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NO= DES]; > > static inline u32 encode_tail(int cpu, int idx) > { > diff --git a/tools/testing/selftests/bpf/libarena/src/common.bpf.c b/tool= s/testing/selftests/bpf/libarena/src/common.bpf.c > index 50be57213dfb..06481f2a2892 100644 > --- a/tools/testing/selftests/bpf/libarena/src/common.bpf.c > +++ b/tools/testing/selftests/bpf/libarena/src/common.bpf.c > @@ -8,6 +8,13 @@ const volatile u32 zero =3D 0; > > struct buddy __arena buddy; > > +/* > + * Storage for the queue nodes declared by bpf_arena_spin_lock.h. Each p= rogram > + * linking the arena spinlock provides exactly one definition, so that t= he array > + * is emitted once rather than once per translation unit. > + */ > +struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES]; > + > int arena_fls(__u64 word) > { > if (!word) > diff --git a/tools/testing/selftests/bpf/progs/arena_spin_lock.c b/tools/= testing/selftests/bpf/progs/arena_spin_lock.c > index cf7cda79c16c..92e75ec3844c 100644 > --- a/tools/testing/selftests/bpf/progs/arena_spin_lock.c > +++ b/tools/testing/selftests/bpf/progs/arena_spin_lock.c > @@ -23,6 +23,13 @@ int cs_count; > #if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CA= ST) > arena_spinlock_t __arena lock; > int test_skip =3D 1; > + > +/* > + * Storage for the queue nodes declared by bpf_arena_spin_lock.h. Each p= rogram > + * linking the arena spinlock provides exactly one definition; libarena'= s lives > + * in libarena/src/common.bpf.c. > + */ > +struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES]; > #else > int test_skip =3D 2; > #endif