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Subject: Re: [PATCH] mm,slab,vmscan: accumulate gradual pressure on small slabs Thread-Topic: [PATCH] mm,slab,vmscan: accumulate gradual pressure on small slabs Thread-Index: AQHUt0DNW/N3hHmpU0+8/TF4YJ27XaXFFWyA Date: Mon, 28 Jan 2019 19:45:09 +0000 Message-ID: <20190128194502.GA30061@castle.DHCP.thefacebook.com> References: <20190128143535.7767c397@imladris.surriel.com> In-Reply-To: <20190128143535.7767c397@imladris.surriel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: MWHPR1401CA0010.namprd14.prod.outlook.com (2603:10b6:301:4b::20) To BYAPR15MB2631.namprd15.prod.outlook.com (2603:10b6:a03:152::24) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:180::1:b22f] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;BYAPR15MB2536;20:iBlr0/ip04jZsBqu1kZesOvkbYzfkihbuHywrAyaOPIl1xNGpPr3njQa2W1EJ5Ptmr3juhsJK2Era7OdEEDD4s5+clVuNnQYgqPqWLifAJhrDZiaE4NQJ1lobyr3aNMuzBlT0M7uMTehuBEdhd0B0aiexK3gvT1L1iFFZ4jxdjc= x-ms-office365-filtering-correlation-id: 53b5d469-98d8-49c0-e4f3-08d685591c70 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600110)(711020)(4605077)(2017052603328)(7153060)(7193020);SRVR:BYAPR15MB2536; x-ms-traffictypediagnostic: BYAPR15MB2536: x-microsoft-antispam-prvs: x-forefront-prvs: 0931CB1479 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(346002)(366004)(39860400002)(136003)(376002)(396003)(189003)(199004)(76176011)(52116002)(97736004)(81156014)(446003)(25786009)(46003)(8676002)(53936002)(81166006)(476003)(7736002)(305945005)(54906003)(6916009)(6246003)(4326008)(33896004)(2906002)(86362001)(11346002)(316002)(99286004)(256004)(186003)(486006)(8936002)(68736007)(105586002)(71200400001)(106356001)(14454004)(33656002)(1076003)(229853002)(386003)(9686003)(6512007)(71190400001)(6486002)(6436002)(478600001)(6506007)(102836004)(6116002)(142933001);DIR:OUT;SFP:1102;SCL:1;SRVR:BYAPR15MB2536;H:BYAPR15MB2631.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;MX:1;A:1; received-spf: None (protection.outlook.com: fb.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: jw0lE7XldqByeR1JkYot52Iu4wRPJ3J5Ia3XGfa5JSJb6Dc2kAUenDNnYcQ8o6sBaPiHCpXnlNcTroIqkOeiIljsDKYoc6GUEWoU0UO+COpK87V0BQwUwUHAfm5ZTNZJyosapuExSkRD6LpADwYMhPH2peMwMMkJEWVGPyh+981RwD/Toz64qKgd5Woh30f71K+hSW2lifewdKjLxaRE22N2WPQ+JPJAPiwQEtk7FuNEytrm2ZWen8bSPuTWDxGL7xsfmCMcEq3+LWkBK2eACUtdhJJSIK2HhFgpcGrL9AjsxvIuFi6vTQjmjC3GSW72SAEj7z7KuPMwNl5RZf0ORV5wNTHEoWb3A8rHvrZgi+wyS/vXIyXB8/txJzZ4yhKpxbDFrLYB2tfigkShnoJII4NxfUhcB3vXwEE9JhPfBIg= Content-Type: text/plain; charset="us-ascii" Content-ID: <76A242FEEB281C4FB87A8E48DEF7F215@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 53b5d469-98d8-49c0-e4f3-08d685591c70 X-MS-Exchange-CrossTenant-originalarrivaltime: 28 Jan 2019 19:45:08.7122 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2536 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-28_10:,, signatures=0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 28, 2019 at 02:35:35PM -0500, Rik van Riel wrote: > There are a few issues with the way the number of slab objects to > scan is calculated in do_shrink_slab. First, for zero-seek slabs, > we could leave the last object around forever. That could result > in pinning a dying cgroup into memory, instead of reclaiming it. > The fix for that is trivial. >=20 > Secondly, small slabs receive much more pressure, relative to their > size, than larger slabs, due to "rounding up" the minimum number of > scanned objects to batch_size. >=20 > We can keep the pressure on all slabs equal relative to their size > by accumulating the scan pressure on small slabs over time, resulting > in sometimes scanning an object, instead of always scanning several. >=20 > This results in lower system CPU use, and a lower major fault rate, > as actively used entries from smaller caches get reclaimed less > aggressively, and need to be reloaded/recreated less often. >=20 > Fixes: 4b85afbdacd2 ("mm: zero-seek shrinkers") > Fixes: 172b06c32b94 ("mm: slowly shrink slabs with a relatively small num= ber of objects") > Cc: Johannes Weiner > Cc: Chris Mason > Cc: Roman Gushchin > Cc: kernel-team@fb.com > Tested-by: Chris Mason Hi, Rik! There is a couple of formatting issues (see below), but other than that the patch looks very good to me. Thanks! Acked-by: Roman Gushchin > --- > include/linux/shrinker.h | 1 + > mm/vmscan.c | 16 +++++++++++++--- > 2 files changed, 14 insertions(+), 3 deletions(-) >=20 > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > index 9443cafd1969..7a9a1a0f935c 100644 > --- a/include/linux/shrinker.h > +++ b/include/linux/shrinker.h > @@ -65,6 +65,7 @@ struct shrinker { > =20 > long batch; /* reclaim batch size, 0 =3D default */ > int seeks; /* seeks to recreate an obj */ > + int small_scan; /* accumulate pressure on slabs with few objects */ > unsigned flags; > =20 > /* These are for internal use */ > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a714c4f800e9..0e375bd7a8b6 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -488,18 +488,28 @@ static unsigned long do_shrink_slab(struct shrink_c= ontrol *shrinkctl, > * them aggressively under memory pressure to keep > * them from causing refetches in the IO caches. > */ > - delta =3D freeable / 2; > + delta =3D (freeable + 1)/ 2; ^ A space is missing here. > } > =20 > /* > * Make sure we apply some minimal pressure on default priority > - * even on small cgroups. Stale objects are not only consuming memory > + * even on small cgroups, by accumulating pressure across multiple > + * slab shrinker runs. Stale objects are not only consuming memory > * by themselves, but can also hold a reference to a dying cgroup, > * preventing it from being reclaimed. A dying cgroup with all > * corresponding structures like per-cpu stats and kmem caches > * can be really big, so it may lead to a significant waste of memory. > */ > - delta =3D max_t(unsigned long long, delta, min(freeable, batch_size)); > + if (!delta) { > + shrinker->small_scan +=3D freeable; > + > + delta =3D shrinker->small_scan >> priority; > + shrinker->small_scan -=3D delta << priority; > + > + delta *=3D 4; > + do_div(delta, shrinker->seeks); > + This empty line can be removed, I believe. > + } > =20 > total_scan +=3D delta; > if (total_scan < 0) { >=20