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Tue, 27 Oct 2026 14:22:30 -0700 (PDT) Received: from localhost ([153.61.198.242]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eae6454a37sm14851685ad.3.2026.10.27.14.22.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2026 14:22:30 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Tue, 27 Oct 2026 21:22:30 +0000 Message-Id: To: "Kumar Kartikeya Dwivedi" Cc: "Andrii Nakryiko" , , , , Subject: Re: [PATCH bpf 16/81] libbpf: Make arena 1 Gbyte when max_entries is not set From: "Alexei Starovoitov" In-Reply-To: References: <20261026025943.404450-1-alexei.starovoitov@gmail.com> <20261026025943.404450-17-alexei.starovoitov@gmail.com> Content-Transfer-Encoding: 8bit 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 On Tue, Oct 27, 2026 at 02:11 PM Kumar Kartikeya Dwivedi wrote: >> The reason I didn't go with 4G since 4k pages on x86 need 8Mbyte >> of kernel memory for empty arena while 1G needs 2Mbyte, which felt ok-ish. > > I re-read the current code (even with your patches in this set), my > understanding is that regardless of max_entries, we always commit 8MB > of page tables, no? I don't see anything that uses max_entries to > decide that bit. So I think this patch is noop regardless. ohh. populate_pgtable_except_pte() doesn't look at max_entries :( sigh. ok let's do 4G then. The only remaining question is whether to do it libbpf or kernel. I lean toward libbpf, since it's easier to revisit if/when we fix populate_pgtable_except_pte() not to waste memory.