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Wed, 9 Dec 2020 02:21:23 +0000 Date: Tue, 8 Dec 2020 18:21:18 -0800 From: Roman Gushchin To: Muchun Song CC: , , , , , , , , , , , Subject: Re: [PATCH v2] mm: memcontrol: optimize per-lruvec stats counter memory usage Message-ID: <20201209022118.GB2385286@carbon.DHCP.thefacebook.com> References: <20201208095132.79383-1-songmuchun@bytedance.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201208095132.79383-1-songmuchun@bytedance.com> X-Originating-IP: [2620:10d:c090:400::5:1ac1] X-ClientProxiedBy: MWHPR17CA0060.namprd17.prod.outlook.com (2603:10b6:300:93::22) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.DHCP.thefacebook.com (2620:10d:c090:400::5:1ac1) by MWHPR17CA0060.namprd17.prod.outlook.com (2603:10b6:300:93::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3654.12 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?3qxED1pfJC8NlzbU795aP+324sQUAYN+ANlAKuiVf9U+qBw4pjuAoPcFNYVV?= =?us-ascii?Q?glV45nAxR+kTmCxnxwg6sbUqllX9yr6ZE2hZOfGeDltN/CwM68qJ1Dov91mQ?= =?us-ascii?Q?pjckXv0B/XsETUSpPNtRqmZVCzKtj145iBLQ5/WB+iSGDAtBuuGRcGepMVp7?= =?us-ascii?Q?P9kihwIOFKq33AUjptD/1L5Z8vFJTvkFoCpd7pbgXxNtC1DtO2rDc801ausS?= =?us-ascii?Q?6rS5LJlRf5I43cfcb5KfU00loMLuQVQ29QFr/DzqaDIqEn4J48nGoiwXSskh?= =?us-ascii?Q?rAlXT//MIg6AxxsJGqloAkr26WyjarO69jbWt3A4v17e8wqvt+qOmhk0U/nL?= =?us-ascii?Q?rQf4rZJ1FajwyoWku50lP0zV6L3o4BvmJy48kSSqyHh3es57u76lRerSDgGe?= =?us-ascii?Q?GWeqpl0yOCsmGH0Nf4d4oCC/xUXoxlWC/hkxUUAjI/92b//hQZ7kgmeS//aQ?= =?us-ascii?Q?234YkvqDFUninVDVfA7iP//c2yYol/oOk7H9EO8+DCkv2S18Cwf+++GwbBEk?= =?us-ascii?Q?4VYKq/IYqXiDYuvGuc+hkpb6GktOK2uNbJ8tkoNNYI8dXnbLQYXcBXv4bik7?= =?us-ascii?Q?kfeV+lMH3mkRdeOwYm7fpBCkfmLYC2lv9koHOfvPyxVR/IoS/5+NQldA+xID?= =?us-ascii?Q?4yPf+88iaVsKwmYiwqXYsxyA4IB8efGDRedQF2sPYi5FU5aNaLDkaNJuD5YU?= =?us-ascii?Q?jDr9rMB1y05AZMCofOVeFVVLewDAkEelK8m7j1XmdqDRMuKmVikkmJHNv+AI?= =?us-ascii?Q?US/zsouiwow3tqOxPJvR3yilMSe2S0jm9gJNlEzHPv5gCj7yH0XjFHTJXOrP?= =?us-ascii?Q?XP6oLFUZvKbYEA4QQKdSEMxLzCT8+F05VlH6sAiZB8DxhtFnwJDP3IuKg9qw?= =?us-ascii?Q?7y0yQDyiSiaW7Kp1ZmbDoZ3ET5s2Qsc2ZSO5uofgoT1n3PDI0fStYM7s7AaQ?= =?us-ascii?Q?f+qy213QNPneEnhZ11GeBZYlJC8ArG5nnR/X8JBe8wl8NWypOBF2Vuufra/J?= =?us-ascii?Q?QgFv7rma/H2SkwjV6t4fHlBPGA=3D=3D?= X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Dec 2020 02:21:23.8513 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-Network-Message-Id: d1635f64-abb6-4169-30f0-08d89be91ff5 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: mkl9Ov2alxVhLhMHNkPg7cdXFAN6tj8Mvo87JurfNOtTq9Y6hCjfQy2STTlN1Sow X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2599 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2020-12-09_02:2020-12-08,2020-12-09 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 phishscore=0 adultscore=0 spamscore=0 suspectscore=1 lowpriorityscore=0 mlxscore=0 clxscore=1011 mlxlogscore=954 malwarescore=0 impostorscore=0 bulkscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012090013 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, Dec 08, 2020 at 05:51:32PM +0800, Muchun Song wrote: > The vmstat threshold is 32 (MEMCG_CHARGE_BATCH), so the type of s32 > of lruvec_stat_cpu is enough. And introduce struct per_cpu_lruvec_stat > to optimize memory usage. > > The size of struct lruvec_stat is 304 bytes on 64 bits system. As it > is a per-cpu structure. So with this patch, we can save 304 / 2 * ncpu > bytes per-memcg per-node where ncpu is the number of the possible CPU. > If there are c memory cgroup (include dying cgroup) and n NUMA node in > the system. Finally, we can save (152 * ncpu * c * n) bytes. Honestly, I'm not convinced. Say, ncpu = 32, n = 2, c = 500. We're saving <5Mb of memory. If the machine has 128Gb of RAM, it's .000000003%. Using longs (s64) allows not to think too much about overflows and can also be slightly faster on 64-bit machines. Thanks!