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Tue, 03 Nov 2026 23:35:11 -0800 (PST) Received: from localhost ([2a03:2880:10ff:50::]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-67bee202bc4sm977299d50.4.2026.11.03.23.35.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Nov 2026 23:35:10 -0800 (PST) X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 04 Nov 2026 08:35:09 +0100 Message-Id: Cc: , , Subject: Re: [PATCH bpf-next v3 00/14] bpf: A stack in arena From: "Kumar Kartikeya Dwivedi" To: "Alexei Starovoitov" , X-Mailer: aerc 0.22.0 References: <20261104012401.1354861-1-alexei.starovoitov@gmail.com> In-Reply-To: On Wed Nov 4, 2026 at 4:31 AM CET, Alexei Starovoitov wrote: > On Tue, Nov 03, 2026 at 05:24 PM Alexei Starovoitov wrote: >> No released compiler emits this code. The change to the BPF backend of L= LVM >> is in review: https://github.com/llvm/llvm-project/pull/235577 > > The flags are made for Rust. I tried them on C. > C without __arena works. The kernel side of this series is enough for it. > The LLVM side needs more work. > > -- libarena without __arena -- > > '#define __arena' is empty. The compiler moves the globals, the heap and > the locals to arena. > > 63 libarena progs out of 63 pass the verifier. > > The price against libarena with __arena: two times more casts, JITed code > +18%, arena_malloc() +7%. > > So probably not a recommended approach, but works for "lazy" C developers= . Could you elaborate on this? Are the extra casts due to the fact that globa= ls, heaps, and locals on the stack are moving to arena memory? My understanding= is that 1-1, the compiler approach is still more efficient in terms of the cas= ts emitted (and 32-bit narrowing) vs BPF_F_ARENA_SCALAR.