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b=sAVdGaiYIqmFPMb237e+e2rLHhbk6C1T5tXs8tS0am3d4NjFmk0P8DtOT0G0S0KRY EYkC1Ccnl9LvqnT+geDFMUbhN+aRUFQGqMOzYqRkTYRUUaB4gI5xH1EKhAgAHdVNlS uIIR55jIq5OBdHuGHZsuxo+cgAvA5lXRI4wOVktQO0qf8TaroYo+hJnn54KXsqtKUt sS89hDW6xOf5pUvUg79dFM+vQtsUN+AF3H7cs2GQUykNVvDIsPJDwwgK1B4zH+uFSY q3dJ6G9C/Y36sNbVIdtq5kE5oU85vlZJXFUNPAJkSEAsghLTZrTzoK9mhuVcvRvPX4 yMI4yJFye4rIw== From: SeongJae Park To: Joshua Hahn Cc: SeongJae Park , Andrew Morton , Daniel Palmer , 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 Subject: Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG_MMU Date: Fri, 19 Dec 2025 18:41:58 -0800 Message-ID: <20251220024158.43433-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: kqd8rgey6eb3brnnsosyj6fw54xbh9u4 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 585252000B X-HE-Tag: 1766198528-227219 X-HE-Meta: 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 FsIEMQgq Oca9bQ7bcJYsFQazmhcn7HkmV+z8j3oC8ZD8+JK0RrbyAzWe387LcokTldl1ZCaQM/+6qSaWPZxoOHMnqHkpKyDcYMe3SdS0ZuUasvV0v1313tDGHEgbWtshMAcj7yCZJsnWBpJU+QU3cN8PUCzHk0tYcTww3mrzX4FRtja8E8GaPzsu6TluwHTOaJ2j6u5JPLyc5taUXBwmjoy+VPrL6vP81O4GpESbnWp0czWdmWx9kTVBwjZHo+l+zw4LLF8Zxiq6P+wZ1aJBAtb8NSO4NnDghDDcmgO2f0hAaf7pXGNfwhFaZHSQen16/vygylNITr9HUhCaO1q8hEdxT1i2CNFiym0m++Cc8fRhjwSnnC5p+o9jPCjrx53yN16uwuTY0TGRQAX+Tyop6HtL2X/og0bV3ngBOX1j01hI5UBlvSdwJ0g6lQ9cIfaCOKKAiZr7Mx2iSUuB+FY0drFhYziTqglrUwBZUnsBx7Yi/ 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, 18 Dec 2025 00:31:59 -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 Acked-by: SeongJae Park Thanks, SJ [...]