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Wed, 21 Oct 2020 20:32:36 +0000 Date: Wed, 21 Oct 2020 13:32:31 -0700 From: Roman Gushchin To: Shakeel Butt CC: , Linux MM , LKML , LTP List , Johannes Weiner , Andrew Morton , Christoph Lameter , Michal Hocko , Tejun Heo , Vlastimil Babka Subject: Re: [PATCH v3] mm: memcg/slab: Stop reparented obj_cgroups from charging root Message-ID: <20201021203231.GB300658@carbon.dhcp.thefacebook.com> References: <87lfg2ob83.fsf@suse.de> <20201019095812.25710-1-rpalethorpe@suse.com> <87mu0hwik7.fsf@suse.de> <87eeltvwg4.fsf@suse.de> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Originating-IP: [2620:10d:c090:400::5:5b8e] X-ClientProxiedBy: MWHPR21CA0034.namprd21.prod.outlook.com (2603:10b6:300:129::20) 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::5:5b8e) by MWHPR21CA0034.namprd21.prod.outlook.com (2603:10b6:300:129::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3499.17 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 8fa12978-4caf-45f0-26c3-08d876007232 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Oct 2020 20:32:36.3000 (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: n4KsohI7cEHjPD2pZ2mIoyqvvnHAe2+h+lezoc4yE1SEbMI8C4tFGagqDqkXsPPQ X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2341 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.737 definitions=2020-10-21_12:2020-10-20,2020-10-21 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxlogscore=999 lowpriorityscore=0 bulkscore=0 spamscore=0 mlxscore=0 phishscore=0 clxscore=1011 adultscore=0 priorityscore=1501 suspectscore=1 malwarescore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2010210141 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 20, 2020 at 09:56:51AM -0700, Shakeel Butt wrote: > On Tue, Oct 20, 2020 at 6:49 AM Richard Palethorpe wrote: > > > > Hello, > > > > Richard Palethorpe writes: > > > > > Hello Shakeel, > > > > > > Shakeel Butt writes: > > >>> > > >>> V3: Handle common case where use_hierarchy=1 and update description. > > >>> > > >>> mm/memcontrol.c | 7 +++++-- > > >>> 1 file changed, 5 insertions(+), 2 deletions(-) > > >>> > > >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > >>> index 6877c765b8d0..34b8c4a66853 100644 > > >>> --- a/mm/memcontrol.c > > >>> +++ b/mm/memcontrol.c > > >>> @@ -291,7 +291,7 @@ static void obj_cgroup_release(struct percpu_ref *ref) > > >>> > > >>> spin_lock_irqsave(&css_set_lock, flags); > > >>> memcg = obj_cgroup_memcg(objcg); > > >>> - if (nr_pages) > > >>> + if (nr_pages && (!mem_cgroup_is_root(memcg) || memcg->use_hierarchy)) > > >> > > >> If we have non-root memcg with use_hierarchy as 0 and this objcg was > > >> reparented then this __memcg_kmem_uncharge() can potentially underflow > > >> the page counter and give the same warning. > > > > > > Yes, although the kernel considers such a config to be broken, and > > > prints a warning to the log, it does allow it. > > > > Actually this can not happen because if use_hierarchy=0 then the objcg > > will be reparented to root. > > > > Yup, you are right. I do wonder if we should completely deprecate > use_hierarchy=0. +1 Until that happy time maybe we can just link all page counters to root page counters if use_hierarchy == false? That would solve the original problem without complicating the code in the main use_hierarchy == true mode. Are there any bad consequences, which I miss? Thanks! -- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 2636f8bad908..fbbc74b82e1a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5339,17 +5339,22 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) memcg->swappiness = mem_cgroup_swappiness(parent); memcg->oom_kill_disable = parent->oom_kill_disable; } - if (parent && parent->use_hierarchy) { + if (!parent) { + page_counter_init(&memcg->memory, NULL); + page_counter_init(&memcg->swap, NULL); + page_counter_init(&memcg->kmem, NULL); + page_counter_init(&memcg->tcpmem, NULL); + } else if (parent->use_hierarchy) { memcg->use_hierarchy = true; page_counter_init(&memcg->memory, &parent->memory); page_counter_init(&memcg->swap, &parent->swap); page_counter_init(&memcg->kmem, &parent->kmem); page_counter_init(&memcg->tcpmem, &parent->tcpmem); } else { - page_counter_init(&memcg->memory, NULL); - page_counter_init(&memcg->swap, NULL); - page_counter_init(&memcg->kmem, NULL); - page_counter_init(&memcg->tcpmem, NULL); + page_counter_init(&memcg->memory, &root_mem_cgroup->memory); + page_counter_init(&memcg->swap, &root_mem_cgroup->swap); + page_counter_init(&memcg->kmem, &root_mem_cgroup->kmem); + page_counter_init(&memcg->tcpmem, &root_mem_cgroup->tcpmem); /* * Deeper hierachy with use_hierarchy == false doesn't make * much sense so let cgroup subsystem know about this