From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id C0EEE383327
	for <linux-kernel@vger.kernel.org>; Wed, 13 May 2026 02:11:25 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1778638287; cv=none; b=ssWyu4urZ31MCNRJnkLQMGayS7njoXunMP/e0fjGN0XAl1az35KnADhIBHItsxtwCsTMRpEiuytzGvGv5oRK5p4JaWg/nsz8SsgbQKL0W6CZX7XqXzLOea2mJpEgRbZUjfHxyBjRC572fTvwzZ5Ibjuk1K0qpzIDroheSiEYlcI=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1778638287; c=relaxed/simple;
	bh=Hm/lAQiIy+pVefFWoYgSJPXdCymAZxPad21Ew7EoX6A=;
	h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From:
	 In-Reply-To:Content-Type; b=pSkcGhXQE9UOxxx0vAZkP9ky914JzW501aY1gfKK6wpSuoWMZEWJEGjeo9w/RewtdQIkXr/MLaxDgtaPZUzo0jDpQb0pc5inwRtQGQRI0tgTfm7LVHOlX9H12jv2+gnockO+SR3q+Fyi4sOQ4U5ws0WPh9Ad82BGtBDp1gRKv/Q=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=wqU8qVBO; arc=none smtp.client-ip=95.215.58.174
Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev
Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="wqU8qVBO"
Message-ID: <0e1b8994-944d-4dda-8966-3cd43661796d@linux.dev>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1;
	t=1778638273;
	h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
	 to:to:cc:cc:mime-version:mime-version:content-type:content-type:
	 content-transfer-encoding:content-transfer-encoding:
	 in-reply-to:in-reply-to:references:references;
	bh=Iq7jnY+N0UwU1xXxCmM5jCZ1Y+zQ9eUrIz+WkKBogEQ=;
	b=wqU8qVBOB6nPI8tTv2ruSJGtw0S5kRmu9mGb+a0X62ASIwBhuC7sNYjp1hEHRGS3fv0Jke
	/+WG6c1jYbL7dgRhevSmu4bdBQDFFOeMTTgqN5ZN6GRhpq6xKym1chF7TeMNfq3QClKzpJ
	vwBwUHJpWeAQoQn7wwGJ/t8kSeSRdOE=
Date: Wed, 13 May 2026 10:10:34 +0800
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
Subject: Re: [linus:master] [mm] 01b9da291c: stress-ng.switch.ops_per_sec
 67.7% regression
To: Shakeel Butt <shakeel.butt@linux.dev>,
 kernel test robot <oliver.sang@intel.com>
Cc: oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org,
 Andrew Morton <akpm@linux-foundation.org>, David Carlier
 <devnexen@gmail.com>, Allen Pais <apais@linux.microsoft.com>,
 Axel Rasmussen <axelrasmussen@google.com>, Baoquan He <bhe@redhat.com>,
 Chengming Zhou <chengming.zhou@linux.dev>,
 Chen Ridong <chenridong@huawei.com>, David Hildenbrand <david@kernel.org>,
 Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>,
 Harry Yoo <harry.yoo@oracle.com>, Hugh Dickins <hughd@google.com>,
 Imran Khan <imran.f.khan@oracle.com>, Johannes Weiner <hannes@cmpxchg.org>,
 Kamalesh Babulal <kamalesh.babulal@oracle.com>,
 Lance Yang <lance.yang@linux.dev>, Liam Howlett <Liam.Howlett@oracle.com>,
 Lorenzo Stoakes <ljs@kernel.org>, Michal Hocko <mhocko@suse.com>,
 =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
 Mike Rapoport <rppt@kernel.org>, Muchun Song <muchun.song@linux.dev>,
 Muchun Song <songmuchun@bytedance.com>, Nhat Pham <nphamcs@gmail.com>,
 Roman Gushchin <roman.gushchin@linux.dev>,
 Suren Baghdasaryan <surenb@google.com>, Usama Arif <usamaarif642@gmail.com>,
 Vlastimil Babka <vbabka@kernel.org>, Wei Xu <weixugc@google.com>,
 Yosry Ahmed <yosry@kernel.org>, Yuanchu Xie <yuanchu@google.com>,
 Zi Yan <ziy@nvidia.com>, Usama Arif <usama.arif@linux.dev>,
 cgroups@vger.kernel.org, linux-mm@kvack.org
References: <202605121641.b6a60cb0-lkp@intel.com> <agNO8G8tPnPuVrGq@linux.dev>
X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers.
From: Qi Zheng <qi.zheng@linux.dev>
In-Reply-To: <agNO8G8tPnPuVrGq@linux.dev>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Migadu-Flow: FLOW_OUT



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()


> 
> I will try to reproduce and will followup on this.

Thanks! I'll also try to reproduce it locally and work on a fix.