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Mon, 13 Jan 2020 18:00:52 +0000 Received: from SN6PR15MB2446.namprd15.prod.outlook.com ([fe80::615e:4236:ddfa:3d10]) by SN6PR15MB2446.namprd15.prod.outlook.com ([fe80::615e:4236:ddfa:3d10%6]) with mapi id 15.20.2623.015; Mon, 13 Jan 2020 18:00:52 +0000 Received: from [172.30.120.61] (2620:10d:c091:480::1025) by MN2PR14CA0024.namprd14.prod.outlook.com (2603:10b6:208:23e::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2623.9 via Frontend Transport; Mon, 13 Jan 2020 18:00:51 +0000 From: Chris Mason To: Matthew Wilcox CC: "linux-xfs@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "jlayton@kernel.org" , "hch@infradead.org" Subject: Re: [RFC 0/8] Replacing the readpages a_op Thread-Topic: [RFC 0/8] Replacing the readpages a_op Thread-Index: AQHVyieJJr3DU4NMDUiHtIM35/TqzKfozHmAgAAQNgCAAAXGAA== Date: Mon, 13 Jan 2020 18:00:52 +0000 Message-ID: <15C84CC9-3196-441D-94DE-F3FD7AC364F0@fb.com> References: <20200113153746.26654-1-willy@infradead.org> <6CA4CD96-0812-4261-8FF9-CD28AA2EC38A@fb.com> <20200113174008.GB332@bombadil.infradead.org> In-Reply-To: <20200113174008.GB332@bombadil.infradead.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: MailMate (1.13.1r5671) x-clientproxiedby: MN2PR14CA0024.namprd14.prod.outlook.com (2603:10b6:208:23e::29) To SN6PR15MB2446.namprd15.prod.outlook.com (2603:10b6:805:22::25) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c091:480::1025] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6752ab99-e401-4ffa-20dc-08d798528734 x-ms-traffictypediagnostic: SN6PR15MB2432: x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:4714; 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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 6752ab99-e401-4ffa-20dc-08d798528734 X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Jan 2020 18:00:52.0944 (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: RoINcDA8ItYwxe8LOScqcr+Jwub00lTLYkh0XUIDLxOnpccN5ZuS02ASO+p0Reot X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR15MB2432 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-01-13_06:2020-01-13,2020-01-13 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 bulkscore=0 adultscore=0 clxscore=1015 suspectscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-2001130144 X-FB-Internal: deliver Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 13 Jan 2020, at 12:40, Matthew Wilcox wrote: > On Mon, Jan 13, 2020 at 04:42:10PM +0000, Chris Mason wrote: > > I did do a couple of helpers for lists for iomap before deciding the > whole thing was too painful. I didn't look at btrfs until just now,=20 > but, um ... > > int extent_readpages(struct address_space *mapping, struct list_head=20 > *pages, > unsigned nr_pages) > .. > struct page *pagepool[16]; > .. > while (!list_empty(pages)) { > .. > list_del(&page->lru); > if (add_to_page_cache_lru(page, mapping,=20 > page->index, > .. > pagepool[nr++] =3D page; > > you're basically doing exactly what i'm proposing to be the new=20 > interface! > OK, you get one extra page per batch ;-P This is true, I didn't explain that part well ;) Depending on=20 compression etc we might end up poking the xarray inside the actual IO=20 functions, but the main difference is that btrfs is building a single=20 bio. You're moving the plug so you'll merge into single bio, but I'd=20 rather build 2MB bios than merge them. I guess it doesn't feel like enough of a win to justify the churn. If=20 we find a way to do much larger pagevecs, I think this makes more sense. -chris