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Shutemov" CC: Linux-MM , Matthew Wilcox , "Kirill A. Shutemov" , Kernel Team , William Kucharski , "Chad Mynhier" , Mike Kravetz Subject: Re: [PATCH v2 3/3] mm,thp: add read-only THP support for (non-shmem) FS Thread-Topic: [PATCH v2 3/3] mm,thp: add read-only THP support for (non-shmem) FS Thread-Index: AQHVIt4j7T4iE6bxX06HBdgJcq3L56amHDgAgAAC7oA= Date: Fri, 21 Jun 2019 13:08:39 +0000 Message-ID: References: <20190614182204.2673660-1-songliubraving@fb.com> <20190614182204.2673660-4-songliubraving@fb.com> <20190621125810.llsqslfo52nfh5g7@box> In-Reply-To: <20190621125810.llsqslfo52nfh5g7@box> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3445.104.11) x-originating-ip: [2620:10d:c090:180::1:ed23] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: eabfea1e-ab39-41a7-558d-08d6f6499425 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1936; x-ms-traffictypediagnostic: MWHPR15MB1936: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8273; x-forefront-prvs: 0075CB064E x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(366004)(346002)(376002)(136003)(39860400002)(396003)(199004)(189003)(316002)(53936002)(46003)(11346002)(6512007)(256004)(102836004)(229853002)(446003)(6116002)(14444005)(66946007)(99286004)(66476007)(71190400001)(71200400001)(76116006)(76176011)(6506007)(73956011)(476003)(53546011)(2616005)(6486002)(66446008)(66556008)(64756008)(68736007)(305945005)(54906003)(6916009)(6246003)(50226002)(5660300002)(478600001)(36756003)(14454004)(486006)(4326008)(8936002)(6436002)(81156014)(81166006)(7736002)(25786009)(8676002)(33656002)(186003)(2906002)(57306001)(86362001)(142933001);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1936;H:MWHPR15MB1165.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX: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: 8Cd4CYlRuqhCCnwcBNKrFzHEwsrxH1aK8cb8ZBSkWCjKwncKKVnbSvwzIJ1Teowem47BInfk0Rip0VBZCOkU74hYnkU69noB/JlXh8JHIkzKbgAR00M6E9woR3BRes26vkO/s1B17bXUEjCTKJu9zuDpjxFOFqTld+clZql6C49nV/0sybiIb7aV+kXzyufPVeEwVVb6TT3yXfM9awU84BDpTh6UR6f0OJZHtD8yp/XJ/VCxORrRLI897Axvn8IFMUBau/iS8enCDga8M22LXM7mVc8q+O19zT8xdu2w6pB/Ms5mWIYK0WBfyJq92C3uHWCZP1qpHRwORHz1XgWrDAnmS/tBiVMwjTyjxioAdDVvSGK1T60V2OSTXSCyIKxG5bqkTPLUppAk5NAakazgdmUgKmDAnA9LfYWWqBqNa5w= Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: eabfea1e-ab39-41a7-558d-08d6f6499425 X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Jun 2019 13:08:39.6222 (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: songliubraving@fb.com X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1936 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-21_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=844 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906210109 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: Hi Kirill, > On Jun 21, 2019, at 5:58 AM, Kirill A. Shutemov wr= ote: >=20 > On Fri, Jun 14, 2019 at 11:22:04AM -0700, Song Liu wrote: >> This patch is (hopefully) the first step to enable THP for non-shmem >> filesystems. >>=20 >> This patch enables an application to put part of its text sections to TH= P >> via madvise, for example: >>=20 >> madvise((void *)0x600000, 0x200000, MADV_HUGEPAGE); >>=20 >> We tried to reuse the logic for THP on tmpfs. The following functions ar= e >> renamed to reflect the new functionality: >>=20 >> collapse_shmem() =3D> collapse_file() >> khugepaged_scan_shmem() =3D> khugepaged_scan_file() >>=20 >> Currently, write is not supported for non-shmem THP. This is enforced by >> taking negative i_writecount. Therefore, if file has THP pages in the >> page cache, open() to write will fail. To update/modify the file, the >> user need to remove it first. >>=20 >> An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this >> feature. >=20 > Please document explicitly that the feature opens local DoS attack: any > user with read access to file can block write to the file by using > MADV_HUGEPAGE for a range of the file. >=20 > As is it only has to be used with trusted userspace. >=20 > We also might want to have mount option in addition to Kconfig option to > enable the feature on per-mount basis. This behavior has been removed from v3 to v5.=20 Thanks, Song=