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Fri, 27 Dec 2019 23:49:18 +0000 Received: from localhost.localdomain (2620:10d:c090:180::322) by MWHPR11CA0032.namprd11.prod.outlook.com (2603:10b6:300:115::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2581.11 via Frontend Transport; Fri, 27 Dec 2019 23:49:17 +0000 From: Roman Gushchin To: Yafang Shao CC: "hannes@cmpxchg.org" , "mhocko@kernel.org" , "vdavydov.dev@gmail.com" , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , Chris Down , "stable@vger.kernel.org" Subject: Re: [PATCH] mm, memcg: reset memcg's memory.{min, low} for reclaiming itself Thread-Topic: [PATCH] mm, memcg: reset memcg's memory.{min, low} for reclaiming itself Thread-Index: AQHVvLNbLK+Vure78kqR8d/QXQ5M5KfOpxSA Date: Fri, 27 Dec 2019 23:49:18 +0000 Message-ID: <20191227234913.GA6742@localhost.localdomain> References: <1577450633-2098-1-git-send-email-laoar.shao@gmail.com> <1577450633-2098-2-git-send-email-laoar.shao@gmail.com> In-Reply-To: <1577450633-2098-2-git-send-email-laoar.shao@gmail.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: MWHPR11CA0032.namprd11.prod.outlook.com (2603:10b6:300:115::18) To BYAPR15MB2631.namprd15.prod.outlook.com (2603:10b6:a03:150::19) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:180::322] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 600ce710-e53a-4cbe-3e45-08d78b27633c x-ms-traffictypediagnostic: BYAPR15MB3224: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 600ce710-e53a-4cbe-3e45-08d78b27633c X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Dec 2019 23:49:18.3960 (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: Ui/4eiMl6SOEeaINwLFU2PPKmGt1eM7fokxRUrYiOBHCKgcEZa64byqHYreG1OxS X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3224 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-12-27_07:2019-12-24,2019-12-27 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 impostorscore=0 mlxscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 mlxlogscore=999 bulkscore=0 phishscore=0 suspectscore=0 clxscore=1015 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1912270192 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 Fri, Dec 27, 2019 at 07:43:53AM -0500, Yafang Shao wrote: > memory.{emin, elow} are set in mem_cgroup_protected(), and the values of > them won't be changed until next recalculation in this function. After > either or both of them are set, the next reclaimer to relcaim this memcg > may be a different reclaimer, e.g. this memcg is also the root memcg of > the new reclaimer, and then in mem_cgroup_protection() in get_scan_count(= ) > the old values of them will be used to calculate scan count, that is not > proper. We should reset them to zero in this case. >=20 > Here's an example of this issue. >=20 > root_mem_cgroup > / > A memory.max=3D1024M memory.min=3D512M memory.current=3D800M >=20 > Once kswapd is waked up, it will try to scan all MEMCGs, including > this A, and it will assign memory.emin of A with 512M. > After that, A may reach its hard limit(memory.max), and then it will > do memcg reclaim. Because A is the root of this reclaimer, so it will > not calculate its memory.emin. So the memory.emin is the old value > 512M, and then this old value will be used in > mem_cgroup_protection() in get_scan_count() to get the scan count. > That is not proper. >=20 > Fixes: 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim") > Signed-off-by: Yafang Shao > Cc: Chris Down > Cc: Roman Gushchin > Cc: stable@vger.kernel.org > --- > mm/memcontrol.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) >=20 > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 601405b..bb3925d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6287,8 +6287,17 @@ enum mem_cgroup_protection mem_cgroup_protected(st= ruct mem_cgroup *root, > =20 > if (!root) > root =3D root_mem_cgroup; > - if (memcg =3D=3D root) > + if (memcg =3D=3D root) { > + /* > + * Reset memory.(emin, elow) for reclaiming the memcg > + * itself. > + */ > + if (memcg !=3D root_mem_cgroup) { > + memcg->memory.emin =3D 0; > + memcg->memory.elow =3D 0; > + } I'm sorry, that didn't bring it from scratch, but I doubt that zeroing effe= cting protection is correct. Imagine a simple config: a large cgroup subtree with= memory.max set on the top level. Reaching this limit doesn't mean that all protection configuration inside the tree can be ignored. Instead we should respect memory.low/max set by a user on this level (look at the parent =3D=3D root case), maybe clamped by memory.high/max. Thanks!