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Mon, 21 Oct 2019 01:15:57 +0000 From: Roman Gushchin To: Christopher Lameter 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 02/16] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat Thread-Topic: [PATCH 02/16] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat Thread-Index: AQHVhUsFBO4ANGUwi02i8A/g/NqcHqdkJTAAgAAqYAA= Date: Mon, 21 Oct 2019 01:15:57 +0000 Message-ID: <20191021011550.GA8869@castle> References: <20191018002820.307763-1-guro@fb.com> <20191018002820.307763-3-guro@fb.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: MWHPR13CA0018.namprd13.prod.outlook.com (2603:10b6:300:16::28) To BN8PR15MB2626.namprd15.prod.outlook.com (2603:10b6:408:c7::28) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:180::37d5] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: d374320b-f743-4343-0eb3-08d755c439dd x-ms-traffictypediagnostic: BN8PR15MB2723: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:2733; 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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: d374320b-f743-4343-0eb3-08d755c439dd X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Oct 2019 01:15:57.0932 (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: AJIB15GKPJ7ZfNua0GM/g+uiOCJn3hBy4+o5xe17i1tQyTVTw6c+46q8rrfc1bMG X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB2723 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,1.0.8 definitions=2019-10-20_06:2019-10-18,2019-10-20 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 phishscore=0 clxscore=1015 priorityscore=1501 bulkscore=0 suspectscore=0 mlxlogscore=999 lowpriorityscore=0 adultscore=0 impostorscore=0 malwarescore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1910210008 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 Sun, Oct 20, 2019 at 10:44:10PM +0000, Christopher Lameter wrote: > On Thu, 17 Oct 2019, Roman Gushchin wrote: >=20 > > But if some counters are in bytes (and the next commit in the series > > will convert slab counters to bytes), it's not gonna work: > > value in bytes can easily exceed s8 without exceeding the threshold > > converted to bytes. So to avoid overfilling per-cpu caches and breaking > > vmstats correctness, let's use s32 instead. >=20 > This quardruples the cache footprint of the counters and likely has some > influence on performance. But otherwise slab allocation counters will be flushed too often, which will be likely noticeable. I can do custom s32 buffers only for these count= ers, but to me it seems like an unnecessary complication, unless we'll find a clear regression. Sp far I haven't noticed any regression on the set of workloads where I did= test the patchset, but if you know any benchmark or realistic test which can aff= ected by this check, I'll be happy to try. Also, less-than-word-sized operations can be slower on some platforms.