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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: AQHVTXlDuUiBx4u3AUqTmiQ0C68ad6bxcvOAgAAJMAA= Date: Thu, 8 Aug 2019 17:05:57 +0000 Message-ID: <770B3C29-CE8F-4228-8992-3C6E2B5487B6@fb.com> References: <20190807233729.3899352-1-songliubraving@fb.com> <20190807233729.3899352-6-songliubraving@fb.com> <20190808163303.GB7934@redhat.com> In-Reply-To: <20190808163303.GB7934@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:c090:200::3099] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 64da6c24-d59b-4289-fa3f-08d71c22ae62 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1375; x-ms-traffictypediagnostic: MWHPR15MB1375: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:7691; x-forefront-prvs: 012349AD1C x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(396003)(346002)(136003)(39860400002)(366004)(376002)(199004)(189003)(316002)(102836004)(76176011)(6436002)(6486002)(54906003)(8936002)(53936002)(46003)(446003)(2616005)(476003)(11346002)(6116002)(256004)(6512007)(81156014)(66446008)(99286004)(8676002)(7736002)(305945005)(14454004)(5660300002)(81166006)(66556008)(64756008)(229853002)(6246003)(66946007)(66476007)(53546011)(50226002)(6506007)(76116006)(2906002)(6916009)(25786009)(4326008)(86362001)(36756003)(57306001)(186003)(486006)(33656002)(71190400001)(71200400001)(478600001);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1375;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: iuzGOKhDbyWSMp1E8YNtrU60S8AfLnMSCNR1tsfBLC70VFv9eOqIhWI7PtFGTUNUMANB1AkRnueHZafsPAYvT7kqBLOqnyUYIIRm195GQuk3AmiU1VLVsnfAgNP00KNJ0qeC2r1rFXM3UpN0tTg+DBu8+qkmJlKpXL5UHIgzlcpPXEq4Oy1xVyan61kdFlLNykhvb50uRBCxB3PuTA93D0AoomzB8maeK0+UGMR5ELCFkXX8nFR9ABmekcwY6EpgG6HpMarHoyowPZiawbEEK48Lf0zIauJquWunRYX4PljWbc5wn3PDRmIp7kpS5VhZ+eTOg9qk8VtWnqmbxNnE2i2H1gFdY3jdP1w6KBiu8l8NHcSSjNfaQ7TZ68VZjqn4QNdFbqPOF1BVdvJ5JkApzCdGtvanDRlYhsOpblnMK6A= Content-Type: text/plain; charset="us-ascii" Content-ID: <198E67CBD55CAC4D8369860F42CD39C7@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 64da6c24-d59b-4289-fa3f-08d71c22ae62 X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Aug 2019 17:05:57.4193 (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: lYK91ACmAArvjnyBNkWtA2Y0Mqw2FbbMR187gzUMD/DsZO1yir0vpfE02wpTtoPXHXAKtLpISrW7LuyAJ4dg2Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1375 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-08_07:,, 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=683 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908080154 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 8, 2019, at 9:33 AM, Oleg Nesterov wrote: >=20 > On 08/07, 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); >=20 > OK, I do not see anything really wrong... >=20 > a couple of questions below. >=20 >> + 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)) >> + continue; >> + >> + page =3D vm_normal_page(vma, addr, *pte); >> + >> + if (!page || !PageCompound(page)) >> + return; >> + >> + if (!hpage) { >> + hpage =3D compound_head(page); >=20 > OK, >=20 >> + if (hpage->mapping !=3D vma->vm_file->f_mapping) >> + return; >=20 > is it really possible? May be WARN_ON(hpage->mapping !=3D vm_file->f_mapp= ing) > makes more sense ? I haven't found code paths lead to this, but this is technically possible.= =20 This pmd could contain subpages from different THPs. The __replace_page()=20 function in uprobes.c creates similar pmd.=20 Current uprobe code won't really create this problem, because=20 !PageCompound() check above is sufficient. But it won't be difficult to=20 modify uprobe code to break this. For this code to be accurate and safe,=20 I think both this check and the one below are necessary. Also, this code=20 is not on any critical path, so the overhead should be negligible.=20 Does this make sense? Thanks, Song