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Wed, 20 Oct 2021 05:16:17 +0000 Received: from PH7PR11MB5819.namprd11.prod.outlook.com ([fe80::3508:ff4c:362d:579c]) by PH7PR11MB5819.namprd11.prod.outlook.com ([fe80::3508:ff4c:362d:579c%6]) with mapi id 15.20.4608.018; Wed, 20 Oct 2021 05:16:17 +0000 Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline To: =?UTF-8?Q?Michal_Koutn=c3=bd?= Cc: Ming Lei , Tejun Heo , Zefan Li , Johannes Weiner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jens Axboe , Roman Gushchin , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org References: <20211018075623.26884-1-quanyang.wang@windriver.com> <8fdcaded-474e-139b-a9bc-5ab6f91fbd4f@windriver.com> From: Quanyang Wang Message-ID: <4644b5eb-8acf-45ef-e33e-84eee6394a57@windriver.com> Date: Wed, 20 Oct 2021 13:16:01 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: HKAPR03CA0033.apcprd03.prod.outlook.com (2603:1096:203:c9::20) To PH7PR11MB5819.namprd11.prod.outlook.com (2603:10b6:510:13b::9) MIME-Version: 1.0 Received: from [128.224.162.199] (60.247.85.82) by HKAPR03CA0033.apcprd03.prod.outlook.com (2603:1096:203:c9::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4628.13 via Frontend Transport; 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Is that correct? (Perhaps not as I realize, > see below.) Yes, I back to the earlier commit 4bfc0bb2c60e and no memory leak is observed. > > But on second thought, the problem is the missing percpu_ref_exit() in > the (root) cgroup release path and percpu counter would allocate the > percpu_count_ptr anyway, so 4bfc0bb2c60e is only making the leak more > visible. Is this correct? No, the earlier commit 4bfc0bb2c60e introduces a imbalance and the later commit 2b0d3d3e4fcf introduces a visible leak. Thanks, Quanyang > > I agree the commit 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of > percpu_ref in fast path") alone did nothing wrong. > > [On a related (but independent) note, there seems to be an optimization > opportunity in not dealing with cgroup_bpf at all on the non-default > hierarchies.] > > Regards, > Michal >