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From: Eduard Zingerman To: Alexei Starovoitov Cc: bpf , Daniel Borkmann , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Tejun Heo , Barret Rhoden , Johannes Weiner , Lorenzo Stoakes , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , linux-mm , Kernel Team Date: Tue, 13 Feb 2024 14:48:18 +0200 In-Reply-To: References: <20240209040608.98927-1-alexei.starovoitov@gmail.com> <20240209040608.98927-15-alexei.starovoitov@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 A+T7mluw nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv iCTce6yYIygHgUAtJcHozAlgRrL0jz44cggBTcoeXp/atckXK546OugZPnl00J3qmm5uWAznU6T5YDv2vCvAMEbz69ib+kHtnOSBvR0Jb86UZZqSb4ATfwMOWe9htGTjKMb0QQOLK0mTcrk/TtymaG+T4Fsos0kgrxqjgfrxxEhYcVNW8v8HISmFGFbqsJmFbVtgk68BcU0wgF8oFxo7u+XYQDdKbI1uQGNBGKNNQEBDADbQIdo8L3sdSWGQtu+LnFqCZoAbYurZCmUjLV3df1b+sg+GJZvVTmMZnzDP/ADufcbjopBBjGTRAY4L76T2niu2EpjclMMM3mtrOc738Kr3+RvPjUupdkZ1ZEZaWpf4cZm+4wH5GUfyu5pmD5WXX2i1r9XaUjeVtebvbuXWmWI1ZDTfOkiz/6Z0GDSeQeEqx2PXYBcepU7S9UNWttDtiZ0+IH4DZcvyKPUcK3tOj4u8GvO3RnOrglERzNCM/WhVdG1+vgU9fXO83TB/PcfAsvxYSie7u792s/I+yA4XKKh82PSTvTzg2/4vEDGpI9yubkfXRkQN28w+HKF5qoRB8/L1ZW/brlXkNzA6SveJhCnH7aOF0Yezl6TfX27w1CW5Xmvfi7X33V/SPvo0tY1THrO1c+bOjt5F+2/K3tvejmXMS/I6URwa8n1e767y5ErFKyXAYRweE9zarEgpNZTuSIGNNAqK+SiLLXt51G7P30TVavIeB6s2lCt1QKt62ccLqUAEQEAAYkBvAQYAQoAJhYhBMfui64wKUMqp1wmBC4MZXpJYEQJBQJijTUBAhsMBQkDwmcAAAoJEC4MZXpJYEQJkRAMAKNvWVwtXm/WxWoiLnXyF2WGXKoDe5+itTLvBmKcV/b1OKZF1s90V7WfSBz712eFAynEzyeezPbwU8QBiTpZcHXwQni3 IYKvsh7s t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 MIME-Version: 1.0 X-Stat-Signature: 7euu3rzkwmabiak1kkchd5b8yinxe5zt X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 26ED3140007 X-Rspam-User: X-HE-Tag: 1707828502-117953 X-HE-Meta: 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 n5pft75d 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.002696, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2024-02-12 at 18:08 -0800, Alexei Starovoitov wrote: [...] > Since it was a surprising behavior we can make libbpf > to auto-extend max_entries with the number of pages necessary > for arena global vars, but it will be surprising too. >=20 > struct { > __uint(type, BPF_MAP_TYPE_ARENA); > __uint(map_flags, BPF_F_MMAPABLE); > __ulong(map_extra, 2ull << 44); // this is start of user VMA > __uint(max_entries, 1000); // this is length of user VMA in pages > } arena SEC(".maps"); >=20 > if libbpf adds extra pages to max_entries the user_vm_end shifts too > and libbpf would need to mmap() it with that size. > When all is hidden in libbpf it's fine, but still can be a surprise > to see a different max_entries in map_info and bpftool map list. > Not sure which way is user friendlier. Adjusting max_entries would be surprising indeed. On the other hand, it would remove the error condition about "Declared arena map size %zd is too small ...". Probably either way is fine, as long as it is documented. Don't have a strong opinion.