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Wed, 27 Nov 2019 17:27:29 +0000 From: Roman Gushchin To: Michal Hocko CC: "linux-mm@kvack.org" , Andrew Morton , Johannes Weiner , "linux-kernel@vger.kernel.org" , Kernel Team , Christian Borntraeger , "stable@vger.kernel.org" Subject: Re: [PATCH] mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction Thread-Topic: [PATCH] mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction Thread-Index: AQHVo8HY/WnVvAZSgEqkb7BHNOXmHaedMHAAgACaToCAASswgIAAUmsA Date: Wed, 27 Nov 2019 17:27:29 +0000 Message-ID: <20191127172724.GA67742@localhost.localdomain> References: <20191125185453.278468-1-guro@fb.com> <20191126092918.GB20912@dhcp22.suse.cz> <20191126184135.GA66034@localhost.localdomain> <20191127123225.GR20912@dhcp22.suse.cz> In-Reply-To: <20191127123225.GR20912@dhcp22.suse.cz> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: MWHPR04CA0055.namprd04.prod.outlook.com (2603:10b6:300:6c::17) To BN8PR15MB2626.namprd15.prod.outlook.com (2603:10b6:408:c7::28) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:180::991a] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 94d1f737-0475-4b74-b61e-08d7735f143d x-ms-traffictypediagnostic: BN8PR15MB3284: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:6430; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 94d1f737-0475-4b74-b61e-08d7735f143d X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Nov 2019 17:27:29.7079 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 3H6Aji6FoRjAzunqrmRDFI+auY+UeA9N1X2oseD2b2XOPcjUk3l7kSG2/5v9Egf0 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB3284 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-11-27_04:2019-11-27,2019-11-27 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 phishscore=0 spamscore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 mlxlogscore=634 impostorscore=0 priorityscore=1501 clxscore=1015 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1911270143 X-FB-Internal: deliver 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: On Wed, Nov 27, 2019 at 01:32:25PM +0100, Michal Hocko wrote: > On Tue 26-11-19 18:41:41, Roman Gushchin wrote: > > On Tue, Nov 26, 2019 at 10:29:18AM +0100, Michal Hocko wrote: > > > On Mon 25-11-19 10:54:53, Roman Gushchin wrote: > [...] > > > > So in a rare case when not all children kmem_caches are destroyed > > > > at the moment when the root kmem_cache is about to be gone, we need > > > > to wait another rcu grace period before destroying the root > > > > kmem_cache. > > >=20 > > > Could you explain how rare this really is please? > >=20 > > It seems that we don't destroy root kmem_caches with enabled memcg > > accounting that often, but maybe I'm biased here. >=20 > So this happens each time a root kmem_cache is destroyed? Which would > imply that only dynamically created ones? Yes, only dynamically created and only in those cases when destruction of the root cache happens immediately after the deactivation of the non-root cache. Tbh I can't imagine any other case except rmmod after removing the cgroup. Thanks!