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Tue, 12 Jan 2021 17:03:27 +0000 Date: Tue, 12 Jan 2021 09:03:22 -0800 From: Roman Gushchin To: Johannes Weiner CC: Andrew Morton , Tejun Heo , Michal Hocko , , , , Subject: Re: [PATCH] mm: memcontrol: prevent starvation when writing memory.high Message-ID: <20210112170322.GA99586@carbon.dhcp.thefacebook.com> References: <20210112163011.127833-1-hannes@cmpxchg.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210112163011.127833-1-hannes@cmpxchg.org> X-Originating-IP: [2620:10d:c090:400::5:dcd4] X-ClientProxiedBy: MWHPR1701CA0008.namprd17.prod.outlook.com (2603:10b6:301:14::18) 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:dcd4) by MWHPR1701CA0008.namprd17.prod.outlook.com (2603:10b6:301:14::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3763.9 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?8OgSWITBZVFtEcIsxo9dGnZId9ABaivTIAqxX/BlUqbvzdDQnt/HX1AzdTpA?= =?us-ascii?Q?uJuhHnFDnraxWQvvBAT08fJAbvR+kAEeRFrcDxjE2N95AvTZsOyTt2ke1rkg?= =?us-ascii?Q?SAlvb44zgWYjTI4evaZzs2++n7sRkR5abBdNBxg91l2LbmKFa6cVw/4tdB5w?= =?us-ascii?Q?p5sg0ZdYiiOn7bv8c3JgdPJQFy8QZfAPTVo93RZ9c07inccQw7PDZobvzOOe?= =?us-ascii?Q?ozwo8nbFI1LQgvilJiH63EcanifY4/gwkcG0DMtCNGa5V3YC/L0+mMSU2kzf?= =?us-ascii?Q?KFYqEbdnuxuceYFGzhxy/UQQ/LhP2F4bTKJnofUgwqFWh0h/slazDF/wtmvj?= =?us-ascii?Q?PsY9RTX2NpcV9Mh/joHt6WGcyKjhliUoiWO0OKmrrX2pCJWTtpIm8jURxN5+?= =?us-ascii?Q?g6zwUJ+4GTi0qDSiWy47PxfqgRphBgR/+xUn1I8scPzwg5d460HXbbZPdABy?= =?us-ascii?Q?KZuPuqLcgwm3wWf2Wckujo7iJjUkIY3qTfo1p4ebyjKZfS3WX1hnnMATO951?= =?us-ascii?Q?NJxjZ2USjgqDEUiOEg6u60L6/Le1zsdcBvEH0eWfUJHQmKCOArOWfGHbLphy?= =?us-ascii?Q?ZXFdWTIS5o9EGOS8xQ91UWaMKY8XB+56YactgkBpHBEdiJjJ/vdnNW1E/ych?= =?us-ascii?Q?rq6OrKtBTKSNdbm5HTr2ONP7wEpp4JQnYkpeYJC85gdGZCxWN8YJ3tQ7X7g+?= =?us-ascii?Q?JPF2a2IGdIIajNVoCOUJIFUgZLuPthpYCttKm9KrqlAWferusxiA/QSESbS+?= =?us-ascii?Q?31WqzmxSL6jUjnrmjeUu45i8wvQ9NtZmqOb8FxYYqjTrjII/TPndBLHiuwgI?= =?us-ascii?Q?v6bmk8CUJBjcHs/GjbtfV9Nkv1k0RQU0m1buNAKIK8qCEmuSBUFgWJMxqC93?= =?us-ascii?Q?FRpnOCgEpxtKm2sdUsOSzGTkoP03jXvz8kGfWkhlYtpK15MZxWQ/jWVsmoO2?= =?us-ascii?Q?MPQCAPWgZTFSw7v9AYkjhCpZlFvOVAeNv+hOAkyARMHvowAvMZVhyWzA3OAx?= =?us-ascii?Q?xZQZoGvH9JhvihhrSPdLDuuYag=3D=3D?= X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jan 2021 17:03:26.9959 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-Network-Message-Id: c9464682-7f1b-4887-13c4-08d8b71bfab0 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2Cle1W33lpOLI6yXNZ9lsR1H082C7vzw5J0Y86cvm7sHC4oZ50nvVONmQAl2ik/S X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2869 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-12_12:2021-01-12,2021-01-12 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 lowpriorityscore=0 phishscore=0 clxscore=1011 adultscore=0 spamscore=0 priorityscore=1501 mlxscore=0 suspectscore=0 mlxlogscore=999 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101120099 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, Jan 12, 2021 at 11:30:11AM -0500, Johannes Weiner wrote: > When a value is written to a cgroup's memory.high control file, the > write() context first tries to reclaim the cgroup to size before > putting the limit in place for the workload. Concurrent charges from > the workload can keep such a write() looping in reclaim indefinitely. > > In the past, a write to memory.high would first put the limit in place > for the workload, then do targeted reclaim until the new limit has > been met - similar to how we do it for memory.max. This wasn't prone > to the described starvation issue. However, this sequence could cause > excessive latencies in the workload, when allocating threads could be > put into long penalty sleeps on the sudden memory.high overage created > by the write(), before that had a chance to work it off. > > Now that memory_high_write() performs reclaim before enforcing the new > limit, reflect that the cgroup may well fail to converge due to > concurrent workload activity. Bail out of the loop after a few tries. > > Fixes: 536d3bf261a2 ("mm: memcontrol: avoid workload stalls when lowering memory.high") > Cc: # 5.8+ > Reported-by: Tejun Heo > Signed-off-by: Johannes Weiner > --- > mm/memcontrol.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 605f671203ef..63a8d47c1cd3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6275,7 +6275,6 @@ static ssize_t memory_high_write(struct kernfs_open_file *of, > > for (;;) { > unsigned long nr_pages = page_counter_read(&memcg->memory); > - unsigned long reclaimed; > > if (nr_pages <= high) > break; > @@ -6289,10 +6288,10 @@ static ssize_t memory_high_write(struct kernfs_open_file *of, > continue; > } > > - reclaimed = try_to_free_mem_cgroup_pages(memcg, nr_pages - high, > - GFP_KERNEL, true); > + try_to_free_mem_cgroup_pages(memcg, nr_pages - high, > + GFP_KERNEL, true); > > - if (!reclaimed && !nr_retries--) > + if (!nr_retries--) Shouldn't it be (!reclaimed || !nr_retries) instead? If reclaimed == 0, it probably doesn't make much sense to retry. Otherwise the patch looks good to me. Thanks!