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Tue, 19 Aug 2025 08:35:05 -0700 (PDT) From: Joshua Hahn To: Joshua Hahn Cc: Johannes Weiner , Chris Mason , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] mm/page_alloc: Occasionally relinquish zone lock in batch freeing Date: Tue, 19 Aug 2025 08:34:58 -0700 Message-ID: <20250819153459.2088221-1-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20250818185804.21044-1-joshua.hahnjy@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B45C480008 X-Stat-Signature: haoejbfjr3txx8fjh1dspdo33n89t1ke X-HE-Tag: 1755617707-363996 X-HE-Meta: U2FsdGVkX1+8XURTScO0wPDz+axa7VMDojWZLRWa6ZQcYkK/4HepDtrd/qIvGB7yRVwS83QNz87ad6yRg/IV+qhD0mqaLRMsXMJ83iRCmzDys+VdfHSAlAHlqy/4TSGH2PHR4VV1BeyCKd3WNdz5mnLzqEZ5Dm4aFROF30bgv1qUCi3yh+5upjYZ+W1zXix/5V+LgKy05UgxfpwBP/77Yy8teGuPCW+8adngcJC557/I0zRqsWKfRD38qssdPRXKMAhiqb1ol9WNBJ54jVyvUxe9XASycneXNp+UZflzrCRZ+yKp+dDowoqmEkCkf/tZvn04+ztYs/0E98EXPPY/AJg2mSYoOm1w0P21XoPqrrY1QuQsbfsQOwrKfeA6KxkiQIAUSOzSyvhq86Ba8wrGcHaQoOwS8Pe2SGoR7fI2OLCSHyUWeM94mh3NkhATWB+xsIDtZ5nDzd9GuQyzt5/rDg4rLPoVy4gJvVy76FVu2oxl/EZwzNDoYfzuHW+BPrKi0PjswX/7fs47TmP6ACh41l63fJyF8Ky5QdQK4ikCkzo1lagtMQjBl+jTpHAgOBtYoxA0ePOBF5ezLGmxtNgkbAUUYD2QeN2ek7+IbbXfhgPBHsqnMJz1D/okv7iWMw6V0hSQvkBCpErC6Kuj0K6hqwxs4Pjb1wkShH92ejmCL6Yio/4Tlcsgwkmj5nLSSHFikDj6eojdyeS6AuSf/GR7Jo1TdAVrxoQowz9jhVknx4/4j1ZFYE+hP2c9yV4IR2zSdKuGFveCQxuH+QfnF79KwkwFvn+hXUAiJJ2XF6ieMzx5ls2Y0KnHvcrIUESL4SgPg6KJBX7Ao0csfSN5P5W//KjljmpP8IrznsVmsJPF9dUTa6GURXUPSNWgE3bS3e1Kk0aikk457DWtQfjePUqIWUxfJtuW5d2OK+cMukrK9TGalX2GW3dEgLyDOz0yUNBt8jEAThEUdjIfK57y9Qh 2wHJvMTu 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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 Mon, 18 Aug 2025 11:58:03 -0700 Joshua Hahn wrote: Cc-ing Suren, who works at Google, not Gogle. Sorry for the typo! Joshua > While testing workloads with high sustained memory pressure on large machines > (1TB memory, 316 CPUs), we saw an unexpectedly high number of softlockups. > Further investigation showed that the lock in free_pcppages_bulk was being held > for a long time, even being held while 2k+ pages were being freed. > > Instead of holding the lock for the entirety of the freeing, check to see if > the zone lock is contended every pcp->batch pages. If there is contention, > relinquish the lock so that other processors have a change to grab the lock > and perform critical work. > > In our fleet, we have seen that performing batched lock freeing has led to > significantly lower rates of softlockups, while incurring relatively small > regressions (relative to the workload and relative to the variation).