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Fri, 19 Jun 2020 01:08:40 +0000 Date: Thu, 18 Jun 2020 18:08:37 -0700 From: Roman Gushchin To: Shakeel Butt CC: Andrew Morton , Christoph Lameter , Johannes Weiner , Michal Hocko , Linux MM , Vlastimil Babka , Kernel Team , LKML Subject: Re: [PATCH v6 05/19] mm: memcontrol: decouple reference counting from page accounting Message-ID: <20200619010837.GB135965@carbon.dhcp.thefacebook.com> References: <20200608230654.828134-1-guro@fb.com> <20200608230654.828134-6-guro@fb.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BYAPR02CA0024.namprd02.prod.outlook.com (2603:10b6:a02:ee::37) 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::5:32ff) by BYAPR02CA0024.namprd02.prod.outlook.com (2603:10b6:a02:ee::37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3109.22 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 9d20b63b-0be5-4f50-1c45-08d813ed4d51 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jun 2020 01:08:40.1941 (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: qH9ZT4irHAOICR6ItYHM+uqAldFNHLPA9HFYLV2LGSnJSrPnqMIvOM1znubSfXCf X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2390 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-18_21:2020-06-18,2020-06-18 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=1 bulkscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=999 clxscore=1015 cotscore=-2147483648 malwarescore=0 spamscore=0 mlxscore=0 adultscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006190004 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 18, 2020 at 07:55:35AM -0700, Shakeel Butt wrote: > Not sure if my email went through, so, re-sending. > > On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin wrote: > > > > From: Johannes Weiner > > > [...] > > @@ -3003,13 +3004,16 @@ void __memcg_kmem_uncharge_page(struct page *page, int order) > > */ > > void mem_cgroup_split_huge_fixup(struct page *head) > > { > > + struct mem_cgroup *memcg = head->mem_cgroup; > > int i; > > > > if (mem_cgroup_disabled()) > > return; > > > > A memcg NULL check is needed here. Hm, it seems like the only way how it can be NULL is if mem_cgroup_disabled() is true: int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask) { unsigned int nr_pages = hpage_nr_pages(page); struct mem_cgroup *memcg = NULL; int ret = 0; if (mem_cgroup_disabled()) goto out; <...> if (!memcg) memcg = get_mem_cgroup_from_mm(mm); ret = try_charge(memcg, gfp_mask, nr_pages); if (ret) goto out_put; css_get(&memcg->css); commit_charge(page, memcg); Did you hit this issue in reality? The only possible scenario I can imagine is if the page was allocated before enabling memory cgroups. Are you about this case? Otherwise we put root_mem_cgroup there. Thanks!