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Wed, 2 Oct 2019 02:09:11 +0000 From: Roman Gushchin To: =?iso-8859-1?Q?Michal_Koutn=FD?= CC: "linux-mm@kvack.org" , Michal Hocko , Johannes Weiner , "linux-kernel@vger.kernel.org" , Kernel Team , Shakeel Butt , Vladimir Davydov , Waiman Long Subject: Re: [PATCH RFC 00/14] The new slab memory controller Thread-Topic: [PATCH RFC 00/14] The new slab memory controller Thread-Index: AQHVZDNwmo4dH7vFVEWbwj6k0KVokadGDMAAgAC3lQA= Date: Wed, 2 Oct 2019 02:09:11 +0000 Message-ID: <20191002020906.GB6436@castle.dhcp.thefacebook.com> References: <20190905214553.1643060-1-guro@fb.com> <20191001151202.GA6678@blackbody.suse.cz> In-Reply-To: <20191001151202.GA6678@blackbody.suse.cz> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: MWHPR19CA0004.namprd19.prod.outlook.com (2603:10b6:300:d4::14) To BN8PR15MB2626.namprd15.prod.outlook.com (2603:10b6:408:c7::28) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:180::dca2] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 19a30c08-5d78-4362-db44-08d746dd8423 x-ms-traffictypediagnostic: BN8PR15MB3187: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; 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charset="iso-8859-1" Content-ID: <3BF5C1432CAE894293127F4977D6735A@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 19a30c08-5d78-4362-db44-08d746dd8423 X-MS-Exchange-CrossTenant-originalarrivaltime: 02 Oct 2019 02:09:11.7222 (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: NegXxpLMYUkWiJp1X+qrIlTscUe4GotaMPvQCIz9dHzDsfPh5VL7NP8kzzVIScrO X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB3187 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,1.0.8 definitions=2019-10-02_01:2019-10-01,2019-10-02 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxlogscore=900 lowpriorityscore=0 priorityscore=1501 mlxscore=0 phishscore=0 adultscore=0 malwarescore=0 suspectscore=0 clxscore=1011 spamscore=0 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1910020018 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 Tue, Oct 01, 2019 at 05:12:02PM +0200, Michal Koutn=FD wrote: > On Thu, Sep 05, 2019 at 02:45:44PM -0700, Roman Gushchin wr= ote: > > Roman Gushchin (14): > > [...] > > mm: memcg/slab: use one set of kmem_caches for all memory cgroups > From that commit's message: >=20 > > 6) obsoletes kmem.slabinfo cgroup v1 interface file, as there are > > no per-memcg kmem_caches anymore (empty output is printed) >=20 > The empty file means no allocations took place in the particular cgroup. > I find this quite a surprising change for consumers of these stats. >=20 > I understand obtaining the same data efficiently from the proposed > structures is difficult, however, such a change should be avoided. (In > my understanding, obsoleted file ~ not available in v2, however, it > should not disappear from v1.) Well, my assumption is that nobody is using this file for anything except debugging purposes (I might be wrong, if somebody has an automation based on it, please, let me know). A number of allocations of each type per memor= y cgroup is definitely a useful debug information, but currently it barely wo= rks (displayed numbers show mostly the number of allocated pages, not the numbe= r of active objects). We can support it, but it comes with the price, and most users don't really need it. So I don't think it worth it to make all allocations slower just to keep some debug interface working for some cgroup v1 users. Do you have examples when it's really useful and worth extra cpu cost? Unfortunately, we can't enable it conditionally, as a user can switch between cgroup v1 and cgroup v2 memory controllers dynamically. Thanks!