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Thu, 24 Apr 2025 08:50:04 -0700 (PDT) Date: Thu, 24 Apr 2025 08:50:04 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: Harry Yoo cc: Vlastimil Babka , David Rientjes , Andrew Morton , Dennis Zhou , Tejun Heo , Mateusz Guzik , Jamal Hadi Salim , Cong Wang , Jiri Pirko , Vlad Buslov , Yevgeny Kliteynik , Jan Kara , Byungchul Park , linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/7] Reviving the slab destructor to tackle the percpu allocator scalability problem In-Reply-To: <20250424080755.272925-1-harry.yoo@oracle.com> Message-ID: <80208a6c-ec42-6260-5f6f-b3c5c2788fcd@gentwo.org> References: <20250424080755.272925-1-harry.yoo@oracle.com> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="8323329-869478563-1745509804=:2657" X-Rspamd-Queue-Id: C42C7C000A X-Stat-Signature: z79j15gjpsonxd97us5srnkbw8hnrhwr X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1745509805-884415 X-HE-Meta: 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 QmJVO5C3 gPJDc0hnpoT/4MjuuGlVbxETKCgBVf9iIpDUKL9EX/e1W7e0ua8qlJHSEvz2Zu4gTnFRP/MQn+xtVm2AdT6UTPeSAOmdbCE8zNVnwoc5It9+ENmQsTgg8tpCoDBMAKN166OOLwgHKGufXibdYyV3HIFbOMKePqz9VeL9frGA9wR5GVrUhqdorjYHRFV8CoQqrTBqm9jEK4lAntGxpkNMQWDZ4dirJGVhRHcZtbdL6LcqlJfhaKy4yI0Xrd2e1wVRRSKX9qrZ1X2VHQlRbJF9qDf4a1g8SgDuhSCvDN6urM2O93m+KrJO3CV5gELqzKGIAOxyUcMIlGY6WK6C7pKZAOcqVI6RAduNAXg8qv6SHAcxzaTooHOzJgkBGPNOmEdXoxLyOS686Eop1oO9rezALnlvCYI0FHSuKrwI4YBgkMPqsYLSGFOWhEp/qZTRzDxIRdA1p 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: This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-869478563-1745509804=:2657 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT On Thu, 24 Apr 2025, Harry Yoo wrote: > Consider mm_struct: it allocates two percpu regions (mm_cid and rss_stat), > so each allocate–free cycle requires two expensive acquire/release on > that mutex. > We can mitigate this contention by retaining the percpu regions after > the object is freed and releasing them only when the backing slab pages > are freed. Could you keep a cache of recently used per cpu regions so that you can avoid frequent percpu allocation operation? You could allocate larger percpu areas for a batch of them and then assign as needed. --8323329-869478563-1745509804=:2657--