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Tue, 10 Nov 2020 21:51:56 +0000 Date: Tue, 10 Nov 2020 13:51:52 -0800 From: Roman Gushchin To: Andrew Morton CC: , Shakeel Butt , Johannes Weiner , Michal Hocko , Christoph Lameter , , Subject: Re: [PATCH 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab caches with SLAB_ACCOUNT Message-ID: <20201110215152.GA2713540@carbon.dhcp.thefacebook.com> References: <20201110195753.530157-1-guro@fb.com> <20201110195753.530157-2-guro@fb.com> <20201110125008.003fb018e74c40109fd6723f@linux-foundation.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201110125008.003fb018e74c40109fd6723f@linux-foundation.org> X-Originating-IP: [2620:10d:c090:400::5:2408] X-ClientProxiedBy: MWHPR14CA0043.namprd14.prod.outlook.com (2603:10b6:300:12b::29) 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::5:2408) by MWHPR14CA0043.namprd14.prod.outlook.com (2603:10b6:300:12b::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3541.25 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 38408657-00da-44f6-2cf4-08d885c2d7fb X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Nov 2020 21:51:56.7916 (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: wOy1+KItDbKqiBM4Qmiccb/ooGoeUz1hWC0/wZYqXp8Ys8Z+TXcLSKKQru9Vm7l9 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2759 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312,18.0.737 definitions=2020-11-10_08:2020-11-10,2020-11-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 malwarescore=0 mlxlogscore=956 spamscore=0 suspectscore=1 mlxscore=0 bulkscore=0 phishscore=0 clxscore=1015 impostorscore=0 adultscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011100148 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, Nov 10, 2020 at 12:50:08PM -0800, Andrew Morton wrote: > On Tue, 10 Nov 2020 11:57:53 -0800 Roman Gushchin wrote: > > > In general it's unknown in advance if a slab page will contain > > accounted objects or not. In order to avoid memory waste, an > > obj_cgroup vector is allocated dynamically when a need to account > > of a new object arises. Such approach is memory efficient, but > > requires an expensive cmpxchg() to set up the memcg/objcgs pointer, > > because an allocation can race with a different allocation on another > > cpu. > > > > But in some common cases it's known for sure that a slab page will > > contain accounted objects: if the page belongs to a slab cache with a > > SLAB_ACCOUNT flag set. It includes such popular objects like > > vm_area_struct, anon_vma, task_struct, etc. > > > > In such cases we can pre-allocate the objcgs vector and simple assign > > it to the page without any atomic operations, because at this early > > stage the page is not visible to anyone else. > > Was there any measurable performance change from this? A very simplistic benchmark (allocating 10000000 64-bytes objects in a row) shows ~15% win. In the real life it seems that most workloads are not very sensitive to the speed of (accounted) slab allocations.