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Fri, 27 Dec 2019 23:55:43 +0000 Received: from localhost.localdomain (2620:10d:c090:180::4df7) by MWHPR04CA0072.namprd04.prod.outlook.com (2603:10b6:300:6c::34) 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 23:55:41 +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" Subject: Re: [PATCH] mm, memcg: reduce size of struct mem_cgroup by using bit field Thread-Topic: [PATCH] mm, memcg: reduce size of struct mem_cgroup by using bit field Thread-Index: AQHVvLNYf+5CcBvhZkC+qybM+O7YGKfOqN6A Date: Fri, 27 Dec 2019 23:55:42 +0000 Message-ID: <20191227235537.GB6742@localhost.localdomain> References: <1577450633-2098-1-git-send-email-laoar.shao@gmail.com> In-Reply-To: <1577450633-2098-1-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: MWHPR04CA0072.namprd04.prod.outlook.com (2603:10b6:300:6c::34) To BYAPR15MB2631.namprd15.prod.outlook.com (2603:10b6:a03:150::19) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:180::4df7] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 3d988d1d-3f09-4baf-2977-08d78b28482d x-ms-traffictypediagnostic: BYAPR15MB3415: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; 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charset="us-ascii" Content-ID: <1FB37DB234260342A3B16D1710593F2B@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 3d988d1d-3f09-4baf-2977-08d78b28482d X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Dec 2019 23:55:42.3945 (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: kNpo10/L/nredMnVUzu2a/XyR2TX38Wdpy5RHRvqbI8CrH8jATasDAa9VUfbpE8o X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3415 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 lowpriorityscore=0 priorityscore=1501 mlxscore=0 phishscore=0 suspectscore=0 bulkscore=0 malwarescore=0 clxscore=1015 mlxlogscore=778 spamscore=0 adultscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1912270193 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 07:43:52AM -0500, Yafang Shao wrote: > There are some members in struct mem_group can be either 0(false) or > 1(true), so we can define them using bit field to reduce size. With this > patch, the size of struct mem_cgroup can be reduced by 64 bytes in theory= , > but as there're some MEMCG_PADDING()s, the real number may be different, > which is relate with the cacheline size. Anyway, this patch could reduce > the size of struct mem_cgroup more or less. >=20 > Signed-off-by: Yafang Shao > Cc: Roman Gushchin > --- > include/linux/memcontrol.h | 21 ++++++++++++--------- > 1 file changed, 12 insertions(+), 9 deletions(-) >=20 > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index a7a0a1a5..f68a9ef 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -229,20 +229,26 @@ struct mem_cgroup { > /* > * Should the accounting and control be hierarchical, per subtree? > */ > - bool use_hierarchy; > + unsigned int use_hierarchy : 1; > + > + /* Legacy tcp memory accounting */ > + unsigned int tcpmem_active : 1; > + unsigned int tcpmem_pressure : 1; > =20 > /* > * Should the OOM killer kill all belonging tasks, had it kill one? > */ > - bool oom_group; > + unsigned int oom_group : 1; > =20 > /* protected by memcg_oom_lock */ > - bool oom_lock; > - int under_oom; > + unsigned int oom_lock : 1; Hm, looking at the original code, it was clear that oom_lock and under_oom are protected with memcg_oom_lock; but not oom_kill_disable. This information seems to be lost. Also, I'd look at the actual memory savings. Is it worth it? Or it's all eaten by the padding. Thanks! > =20 > - int swappiness; > /* OOM-Killer disable */ > - int oom_kill_disable; > + unsigned int oom_kill_disable : 1; > + > + int under_oom; > + > + int swappiness; > =20 > /* memory.events and memory.events.local */ > struct cgroup_file events_file; > @@ -297,9 +303,6 @@ struct mem_cgroup { > =20 > unsigned long socket_pressure; > =20 > - /* Legacy tcp memory accounting */ > - bool tcpmem_active; > - int tcpmem_pressure; > =20 > #ifdef CONFIG_MEMCG_KMEM > /* Index in the kmem_cache->memcg_params.memcg_caches array */ > --=20 > 1.8.3.1 >=20