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Tue, 8 Sep 2020 19:22:03 +0000 Date: Tue, 8 Sep 2020 12:21:59 -0700 From: Roman Gushchin To: Julius Hemanth Pitti CC: , , , , , , , Subject: Re: [PATCH] mm: memcg: yield cpu when we fail to charge pages Message-ID: <20200908192159.GB567128@carbon.DHCP.thefacebook.com> References: <20200908185051.62420-1-jpitti@cisco.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200908185051.62420-1-jpitti@cisco.com> X-ClientProxiedBy: BYAPR08CA0040.namprd08.prod.outlook.com (2603:10b6:a03:117::17) 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::5:62d5) by BYAPR08CA0040.namprd08.prod.outlook.com (2603:10b6:a03:117::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3370.16 via Frontend Transport; Tue, 8 Sep 2020 19:22:02 +0000 X-Originating-IP: [2620:10d:c090:400::5:62d5] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: bccfcde2-21b3-4704-9efc-08d8542c7730 X-MS-TrafficTypeDiagnostic: BYAPR15MB2663: X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Oob-TLC-OOBClassifiers: OLM:4502; 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On non-preemptive > kernel, when we are OOM, this results in holding > CPU forever. > > On SMP systems, this doesn't create a big problem > because oom_reaper get a change to kill victim > and make some free pages. However on a single-core > CPU (or cases where oom_reaper pinned to same CPU > where try_charge is executing), oom_reaper shall > never get scheduled and we stay in try_charge forever. > > Steps to repo this on non-smp: > 1. mount -t tmpfs none /sys/fs/cgroup > 2. mkdir /sys/fs/cgroup/memory > 3. mount -t cgroup none /sys/fs/cgroup/memory -o memory > 4. mkdir /sys/fs/cgroup/memory/0 > 5. echo 40M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes > 6. echo $$ > /sys/fs/cgroup/memory/0/tasks > 7. stress -m 5 --vm-bytes 10M --vm-hang 0 > > Signed-off-by: Julius Hemanth Pitti > --- > mm/memcontrol.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0d6f3ea86738..4620d70267cb 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2652,6 +2652,8 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > if (fatal_signal_pending(current)) > goto force; > > + cond_resched(); > + Can you, please, add a short comment here? Something like "give oom_reaper a chance on a non-SMP system"? > /* > * keep retrying as long as the memcg oom killer is able to make > * a forward progress or bypass the charge if the oom killer > -- > 2.17.1 > The patch makes total sense to me. Please, feel free to add Acked-by: Roman Gushchin after adding a comment. Thank you!