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From: Shakeel Butt To: Qi Zheng Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , David Carlier , Allen Pais , Axel Rasmussen , Baoquan He , Chengming Zhou , Chen Ridong , David Hildenbrand , Hamza Mahfooz , Harry Yoo , Hugh Dickins , Imran Khan , Johannes Weiner , Kamalesh Babulal , Lance Yang , Liam Howlett , Lorenzo Stoakes , Michal Hocko , Michal =?utf-8?Q?Koutn=C3=BD?= , Mike Rapoport , Muchun Song , Muchun Song , Nhat Pham , Roman Gushchin , Suren Baghdasaryan , Usama Arif , Vlastimil Babka , Wei Xu , Yosry Ahmed , Yuanchu Xie , Zi Yan , Usama Arif , cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [linus:master] [mm] 01b9da291c: stress-ng.switch.ops_per_sec 67.7% regression Message-ID: References: <202605121641.b6a60cb0-lkp@intel.com> <0e1b8994-944d-4dda-8966-3cd43661796d@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0e1b8994-944d-4dda-8966-3cd43661796d@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: A53F916000D X-Rspamd-Server: rspam04 X-Stat-Signature: ur75uydor1ej4maagswau1xxwbk6h1x6 X-HE-Tag: 1778680198-403911 X-HE-Meta: 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 MVkxP0in e+UqDLXyoJktG4GULv7jwZA7obFTCSs/ABXzw5KrDJZmWt/cppI7bKD/wKr3VP/HhvvhYYo5164ah2Yx4jCndj0/pOzjKFuhgHhKkF0xKJwUD8fQDdeta+cy8Vwgzo30WpHd51HQGe1ABArz4cFtHaAqflaJWVi2NeBRotIddG+JLfJUiLFtndAKz81zSn5XLXi3xbk807hW2GBaKBOHdQVO00z9WqyUPCnO9KT0fL+NV8GIP3pcHlAUeLcACIM11F/ex6C6W6n3yTjnrjBfrToihfQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 13, 2026 at 10:10:34AM +0800, Qi Zheng wrote: > > > On 5/13/26 12:03 AM, Shakeel Butt wrote: > > On Tue, May 12, 2026 at 08:56:52PM +0800, kernel test robot wrote: > > > > > > > > > Hello, > > > > > > kernel test robot noticed a 67.7% regression of stress-ng.switch.ops_per_sec on: > > > > > > > > > commit: 01b9da291c4969354807b52956f4aae1f41b4924 ("mm: memcontrol: convert objcg to be per-memcg per-node type") > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master > > > > This is most probably due to shuffling of struct mem_cgroup and struct > > mem_cgroup_per_node members. > > Another possibility is that after objcg was split into per-node, the > slab accounting fast path is still designed assuming only one current > objcg per CPU: > > struct obj_stock_pcp { > struct obj_cgroup *cached_objcg; > }; > > So it's may cause the following thrashing: > > CPU stock cached = memcg/node0 objcg > free object tagged = memcg/node1 objcg > => __refill_obj_stock --> objcg mismatch > => drain_obj_stock() > => cache switches to node1 objcg > > next local allocation tagged = node0 objcg > => mismatch again > => drain_obj_stock() Actually I think this is the issue, we have ping pong threads running on different nodes where though theu are in same cgroup but their current->obcg is for local node and thus this ping pong is thrashing the per-cpu objcg stock. The easier fix would be to compare objcg->memcg instead of just objcg during draining and caching. In addition we can add support for multiple objcg per-cpu stock caching.