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Thu, 18 Dec 2025 07:39:52 -0800 (PST) Received: from server.roeck-us.net ([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-12061f47269sm6851144c88.4.2025.12.18.07.39.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Dec 2025 07:39:51 -0800 (PST) Date: Thu, 18 Dec 2025 07:39:50 -0800 From: Guenter Roeck To: Joshua Hahn Cc: Andrew Morton , Daniel Palmer , 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 Subject: Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG_MMU Message-ID: References: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 88F7920019 X-Stat-Signature: d6txgr76tekwpupc1bbo7ksjtxd5c3dp X-HE-Tag: 1766072393-326334 X-HE-Meta: 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 UuiY89um i4dEZQlzNmSQ8ExhAEaK6EUqjxWbThdvUjIqXJ5xS4UzYnO+i1Ik9KBUZ2lf2TpHnKxjuSBdJxhjr/CyCS2NwAW/lprIpz89l/xqdnMy+ry+b00yWINgnqvleYWH7ynRtfEjP9zGxEVgHcJLoImMjBhxOZvXxXSgPYDXjOwjuzfH4k67h6zacJu8PHcsRUzt0EL42W+0ZWPGSDwP+S7Feo8N+f/afZU7jIfV5mrumMJe+nn8szPJJHWRgAv3R36ycjvv+rNTpW5JVnETMCbgIrMsZqKmYzNtODaJVbTgCPU5uW06lqmDoRIU3Pk7rBCpzLQxjueyhbSrbNy4= 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 Thu, Dec 18, 2025 at 12:31:59AM -0800, 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. > > There is no functional difference expected with this patch before commit > 2783088ef24e, other than the pr_debug in zone_pcp_init now printing out > 1 instead of 0 for zones in NOMMU systems. Not only is this a pr_debug, > the difference is purely semantic anyways. > > Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") > Reported-by: Daniel Palmer > Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/ > Reported-by: Guenter Roeck > Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/ > Signed-off-by: Joshua Hahn Tested-by: Guenter Roeck Guenter