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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: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 33AF04000A X-Stat-Signature: 8ekuk5qjhgpcy7jyni6uwmhk9icfxjrp X-Rspam-User: X-HE-Tag: 1778682452-597671 X-HE-Meta: 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 cSQ3Wiwa dHXnRV/HgQXI1k3MwFi7/4zYtinxnsND207VkHnJijdnrudAgjMmFa3DxAZbZ2Qu+di7te4CtjwPu49NdekC7dpN3Y+zzfCduYQYIwZRtKwhC9us1/fcEBH0G26u9tOskFvUavV2qxNDnRawxRug99cXvxwq3cpBlDlqJXnfrWsKsxTeqXdB9xuLWCW6St2Mk+OZe84HYtonH/TqwKUb7iwpNvit6IA0EX+TjSSl1QMuSLscjus8asPa+tVD3z5tHFJVEWzHHA4e7znuNv6rxpi5WDQ== 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 06:49:45AM -0700, Shakeel Butt wrote: > 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. Something like the following: >From d756abe831a905d6fe32bad9a984fc619dafb7e0 Mon Sep 17 00:00:00 2001 From: Shakeel Butt Date: Wed, 13 May 2026 07:24:55 -0700 Subject: [PATCH] mm/memcontrol: skip obj_stock drain when refilled objcg shares memcg Signed-off-by: Shakeel Butt --- mm/memcontrol.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d978e18b9b2d..01ed7a8e18ac 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3318,6 +3318,7 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, bool allow_uncharge) { + struct obj_cgroup *cached; unsigned int nr_pages = 0; if (!stock) { @@ -3327,7 +3328,18 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, goto out; } - if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ + cached = READ_ONCE(stock->cached_objcg); + if (cached != objcg && + (!cached || obj_cgroup_memcg(cached) != obj_cgroup_memcg(objcg))) { drain_obj_stock(stock); obj_cgroup_get(objcg); stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) -- 2.53.0-Meta