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Thu, 18 Dec 2025 00:32:01 -0800 (PST) From: Joshua Hahn To: Andrew Morton Cc: 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: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG_MMU Date: Thu, 18 Dec 2025 00:31:59 -0800 Message-ID: <20251218083200.2435789-1-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6ED69100008 X-Stat-Signature: pixrsyssa41aka19rtmi6kjgteepm7ro X-Rspam-User: X-HE-Tag: 1766046723-622987 X-HE-Meta: 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 TyuXqtpd 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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: 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 --- v1 --> v2: - Instead of restoring max(1, zone_batchsize(zone)), just return 1 for NOMMU systems since this is simpler and only affects a single pr_debug. mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 822e05f1a964..977cbf20777d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5924,7 +5924,7 @@ static int zone_batchsize(struct zone *zone) * recycled, this leads to the once large chunks of space being * fragmented and becoming unavailable for high-order allocations. */ - return 0; + return 1; #endif } base-commit: 40fbbd64bba6c6e7a72885d2f59b6a3be9991eeb -- 2.47.3