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Mon, 12 Aug 2019 14:36:12 +0000 Received: from MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::79c8:442d:b528:802d]) by MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::79c8:442d:b528:802d%9]) with mapi id 15.20.2157.022; Mon, 12 Aug 2019 14:36:12 +0000 From: Song Liu To: Oleg Nesterov CC: Linux Kernel Mailing List , Linux MM , Andrew Morton , "Matthew Wilcox" , "Kirill A. Shutemov" , Kernel Team , "William Kucharski" , "srikar@linux.vnet.ibm.com" Subject: Re: [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP Thread-Topic: [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP Thread-Index: AQHVTXlDuUiBx4u3AUqTmiQ0C68ad6bxcvOAgAAJMACAAXXfAIAAEp4AgAAZUACABGTDgIAAGOsA Date: Mon, 12 Aug 2019 14:36:11 +0000 Message-ID: <0BD4D364-51BE-4844-8270-9A664C3E6216@fb.com> References: <20190807233729.3899352-1-songliubraving@fb.com> <20190807233729.3899352-6-songliubraving@fb.com> <20190808163303.GB7934@redhat.com> <770B3C29-CE8F-4228-8992-3C6E2B5487B6@fb.com> <20190809152404.GA21489@redhat.com> <3B09235E-5CF7-4982-B8E6-114C52196BE5@fb.com> <4D8B8397-5107-456B-91FC-4911F255AE11@fb.com> <20190812130659.GA31560@redhat.com> In-Reply-To: <20190812130659.GA31560@redhat.com> 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::4519] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 4a8cd62f-1759-4bc8-f835-08d71f326c38 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1151; x-ms-traffictypediagnostic: MWHPR15MB1151: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:5236; x-forefront-prvs: 012792EC17 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(136003)(39860400002)(376002)(396003)(366004)(346002)(199004)(189003)(53936002)(71200400001)(71190400001)(81166006)(81156014)(6486002)(316002)(99286004)(6512007)(5660300002)(50226002)(76116006)(6916009)(2906002)(66446008)(66946007)(229853002)(66556008)(54906003)(66476007)(64756008)(6436002)(8936002)(86362001)(6246003)(36756003)(478600001)(4326008)(102836004)(46003)(256004)(7736002)(14454004)(305945005)(14444005)(33656002)(25786009)(8676002)(6506007)(57306001)(6116002)(76176011)(486006)(186003)(2616005)(53546011)(476003)(11346002)(446003);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1151;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: i4wAFsRZXzhnPe7MTQvDkxTDxK2UyQqZ+7Sd5dZQPcBx+C5D28ZYWqTKMzcJjnxxK0giXUp1ezjsAjyDnyQK0fvvgQiHE4zq4buLNyWR3A56WR4Eh/09PIppt62WEhKr/1Lm53+qd0e6QcG0Tc3iJ1uPWFywNgbtqlXG26fZjWYILEPJvNka7oeY4z8H6gQ/FXD3WOnSa4+9HewUOhqNW39ddy9ha79apSD5Y6WmHREQUJCWyp3ODK2FPo2Rq+4aXrkdKiYogDEJp5rCXrpSx4wszAbqzC8tnU/I0p2h6EZFHxq3z/vapK3cOi+/v/jZx+qalXxT+HO+wTAG/tWdH5aR21f5Ih6lmN9e1TVEfGpeHo6ZRtguK5NSsIwsYYeVEAfUQEFue67WLrXkgofvdcHpPLOCxfIVtjr+zlsClhw= Content-Type: text/plain; charset="us-ascii" Content-ID: <301B9EE7F0B62C438BDA2973ED161B30@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 4a8cd62f-1759-4bc8-f835-08d71f326c38 X-MS-Exchange-CrossTenant-originalarrivaltime: 12 Aug 2019 14:36:11.8614 (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: UbTSrmwvphCxOyn0Z+8eEYjvUUElg6H8sAgMjn12uM97Pvj0XX/phYz18TU/i580J+Dd/26KVInF7C0qGUE48w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1151 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-12_06:,, 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=485 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908120163 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 Aug 12, 2019, at 6:06 AM, Oleg Nesterov wrote: >=20 > On 08/09, Song Liu wrote: >>=20 >> +void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) >> +{ >> + unsigned long haddr =3D addr & HPAGE_PMD_MASK; >> + struct vm_area_struct *vma =3D find_vma(mm, haddr); >> + struct page *hpage =3D NULL; >> + pmd_t *pmd, _pmd; >> + spinlock_t *ptl; >> + int count =3D 0; >> + int i; >> + >> + if (!vma || !vma->vm_file || >> + vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE) >> + return; >> + >> + /* >> + * This vm_flags may not have VM_HUGEPAGE if the page was not >> + * collapsed by this mm. But we can still collapse if the page is >> + * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check() >> + * will not fail the vma for missing VM_HUGEPAGE >> + */ >> + if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE)) >> + return; >> + >> + pmd =3D mm_find_pmd(mm, haddr); >> + if (!pmd) >> + return; >> + >> + /* step 1: check all mapped PTEs are to the right huge page */ >> + for (i =3D 0, addr =3D haddr; i < HPAGE_PMD_NR; i++, addr +=3D PAGE_SI= ZE) { >> + pte_t *pte =3D pte_offset_map(pmd, addr); >> + struct page *page; >> + >> + if (pte_none(*pte) || !pte_present(*pte)) >> + continue; >=20 > if (!pte_present(*pte)) > return; >=20 > you can't simply flush pmd if this page is swapped out. hmm... how about if (pte_none(*pte)) continue; if (!pte_present(*pte)) return; If the page hasn't faulted in for this mm, i.e. pte_none(), we can flush the pmd.=20 >=20 >> + >> + page =3D vm_normal_page(vma, addr, *pte); >> + >> + if (!page || !PageCompound(page)) >> + return; >> + >> + if (!hpage) { >> + hpage =3D compound_head(page); >> + /* >> + * The mapping of the THP should not change. >> + * >> + * Note that uprobe may change the page table, >=20 > Not only uprobe can cow the page. Debugger can do. Or mmap(PROT_WRITE, MA= P_PRIVATE). >=20 > uprobe() is "special" because it a) it works with a foreign mm and b) > it can't stop the process which uses this mm. Otherwise it could simply > update the page returned by get_user_pages_remote(FOLL_FORCE), just we > would need to add FOLL_WRITE and if we do this we do not even need SPLIT, > that is why, say, __access_remote_vm() works without SPLIT. Will update the comment in next version.=20 Thanks! Song