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Thu, 18 Dec 2025 04:30:52 -0800 (PST) MIME-Version: 1.0 References: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> In-Reply-To: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> From: Daniel Palmer Date: Thu, 18 Dec 2025 21:30:42 +0900 X-Gm-Features: AQt7F2rK_7wgkI2apPb4L0y_XrU2_RCv4C7E3ejczHCuGEQQAW2pFOcChHjoj5w Message-ID: Subject: Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG_MMU To: Joshua Hahn Cc: Andrew Morton , Guenter Roeck , 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 Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: sg9gcsmwwgkgrnqx78cjefjk3p11uobi X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 2FC5E1C000E X-Rspam-User: X-HE-Tag: 1766061054-917724 X-HE-Meta: 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 +eb9kUwv JJcqM8EBUKf2pwv5kKrLBXYGhV2hNqKh+aZFRi5naczq/BX6BPL0zxj3G8mkJGEFjHCnzk63xDFlTiYlleRR24q2dgZBQNsWOQJrjo+WMi1g1JWtim9QEvmLiKYAEDIXaRhnemL0DhXqhxxhDs0zgy0CEdnRuHfv6DfnmoMU7o5/bHFekcpK7LDLZVRL7vvI62vcQ9cfPs3Uxq1qmYJmvPfT1a5aJhkhJ8M1ypK05cPYEl6OEktoBcr7qMWCM0CJvyln8Z8dK6BxCVW0qoGtph89mzSyVqRN8pMoqI4n8yju4OdBnXJGVFejJOnrnI2CoKLjbnP1MPWc+fyH6Oxzn1yxCLttqriYg4Xq/ 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: 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.. Thanks! Daniel