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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a2d1612735sm29562065ad.58.2025.12.18.07.39.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Dec 2025 07:39:05 -0800 (PST) Message-ID: <51271dc7-080e-4af6-ba00-9d5b2cd0871f@roeck-us.net> Date: Thu, 18 Dec 2025 07:39:03 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG_MMU To: Daniel Palmer , Joshua Hahn Cc: Andrew Morton , Brendan Jackman , Johannes Weiner , Michal Hocko , Suren Baghdasaryan , Vlastimil Babka , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com References: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAmgrMyQFCSbODQkACgkQyx8mb86fmYGcWRAA oRwrk7V8fULqnGGpBIjp7pvR187Yzx+lhMGUHuM5H56TFEqeVwCMLWB2x1YRolYbY4MEFlQg VUFcfeW0OknSr1s6wtrtQm0gdkolM8OcCL9ptTHOg1mmXa4YpW8QJiL0AVtbpE9BroeWGl9v 2TGILPm9mVp+GmMQgkNeCS7Jonq5f5pDUGumAMguWzMFEg+Imt9wr2YA7aGen7KPSqJeQPpj onPKhu7O/KJKkuC50ylxizHzmGx+IUSmOZxN950pZUFvVZH9CwhAAl+NYUtcF5ry/uSYG2U7 DCvpzqOryJRemKN63qt1bjF6cltsXwxjKOw6CvdjJYA3n6xCWLuJ6yk6CAy1Ukh545NhgBAs rGGVkl6TUBi0ixL3EF3RWLa9IMDcHN32r7OBhw6vbul8HqyTFZWY2ksTvlTl+qG3zV6AJuzT WdXmbcKN+TdhO5XlxVlbZoCm7ViBj1+PvIFQZCnLAhqSd/DJlhaq8fFXx1dCUPgQDcD+wo65 qulV/NijfU8bzFfEPgYP/3LP+BSAyFs33y/mdP8kbMxSCjnLEhimQMrSSo/To1Gxp5C97fw5 3m1CaMILGKCmfI1B8iA8zd8ib7t1Rg0qCwcAnvsM36SkrID32GfFbv873bNskJCHAISK3Xkz qo7IYZmjk/IJGbsiGzxUhvicwkgKE9r7a1rOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAmgrMyQFCSbODQkACgkQyx8mb86fmYHlgg/9 H5JeDmB4jsreE9Bn621wZk7NMzxy9STxiVKSh8Mq4pb+IDu1RU2iLyetCY1TiJlcxnE362kj njrfAdqyPteHM+LU59NtEbGwrfcXdQoh4XdMuPA5ADetPLma3YiRa3VsVkLwpnR7ilgwQw6u dycEaOxQ7LUXCs0JaGVVP25Z2hMkHBwx6BlW6EZLNgzGI2rswSZ7SKcsBd1IRHVf0miwIFYy j/UEfAFNW+tbtKPNn3xZTLs3quQN7GdYLh+J0XxITpBZaFOpwEKV+VS36pSLnNl0T5wm0E/y scPJ0OVY7ly5Vm1nnoH4licaU5Y1nSkFR/j2douI5P7Cj687WuNMC6CcFd6j72kRfxklOqXw zvy+2NEcXyziiLXp84130yxAKXfluax9sZhhrhKT6VrD45S6N3HxJpXQ/RY/EX35neH2/F7B RgSloce2+zWfpELyS1qRkCUTt1tlGV2p+y2BPfXzrHn2vxvbhEn1QpQ6t+85FKN8YEhJEygJ F0WaMvQMNrk9UAUziVcUkLU52NS9SXqpVg8vgrO0JKx97IXFPcNh0DWsSj/0Y8HO/RDkGXYn FDMj7fZSPKyPQPmEHg+W/KzxSSfdgWIHF2QaQ0b2q1wOSec4Rti52ohmNSY+KNIW/zODhugJ np3900V20aS7eD9K8GTU0TGC1pyz6IVJwIE= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 88968180013 X-Rspamd-Server: rspam03 X-Stat-Signature: 3h7d3xesmgwdy7dattcxe7qdbzp4hhud X-Rspam-User: X-HE-Tag: 1766072347-470177 X-HE-Meta: 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 ukGs1At8 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 12/18/25 04:30, Daniel Palmer wrote: > Hi Joshua, > > On Thu, 18 Dec 2025 at 17:32, Joshua Hahn wrote: >> >> Commit 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") >> moved the error handling (0-handling) of zone_batchsize from its >> callers to inside the function. However, the commit left out the error >> handling for the NOMMU case, leading to deadlocks on NOMMU systems. >> >> For NOMMU systems, return 1 instead of 0 for zone_batchsize, which restores >> the previous deadlock-free behavior. > > Tested this on my 68000 setup, filled the memory to cause an OOM and I > got OOM instead of deadlock as expected. > > Tested-by: Daniel Palmer > > FWIW There was a BoF about NOMMU at LPC last week and I did mention to > the people presenting that seem to be using NOMMU in real world > applications that NOMMU was broken in mainline. I hoped they would > have chimed in on this.. > Unrelated to this problem, but I gave up testing NOMMU for arm and xtensa because it was too difficult to maintain the toolchains for it. Guenter