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Shutemov" , Kernel Team , "William Kucharski" , "srikar@linux.vnet.ibm.com" Subject: Re: [PATCH v4 1/2] khugepaged: enable collapse pmd for pte-mapped THP Thread-Topic: [PATCH v4 1/2] khugepaged: enable collapse pmd for pte-mapped THP Thread-Index: AQHVSYiXGgj4LZsXukKr/14r9rTZvabt6SyAgAC4r4A= Date: Tue, 6 Aug 2019 21:03:58 +0000 Message-ID: <38C0FD76-3CA5-4B86-AB31-FDDD72F6C557@fb.com> References: <20190802231817.548920-1-songliubraving@fb.com> <20190802231817.548920-2-songliubraving@fb.com> <20190806100256.GA21454@redhat.com> In-Reply-To: <20190806100256.GA21454@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::2:4454] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6931790b-a5e1-4944-e41a-08d71ab199a4 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1790; x-ms-traffictypediagnostic: MWHPR15MB1790: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:6108; x-forefront-prvs: 0121F24F22 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(136003)(396003)(346002)(39860400002)(376002)(366004)(199004)(189003)(66556008)(2616005)(476003)(50226002)(46003)(486006)(229853002)(446003)(6246003)(5660300002)(66446008)(6486002)(316002)(66946007)(11346002)(64756008)(66476007)(186003)(53936002)(305945005)(6436002)(6512007)(33656002)(25786009)(57306001)(7736002)(68736007)(8936002)(6506007)(102836004)(53546011)(478600001)(86362001)(76176011)(54906003)(4326008)(36756003)(6916009)(76116006)(8676002)(256004)(6116002)(14444005)(2906002)(99286004)(71200400001)(71190400001)(81166006)(14454004)(81156014);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1790;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: wDqnauJb9gKOixGqaxXXVDT4mber2l6Cef5EuDRbV3GPvSrPkTTqmmVvRSCu5aP0BdkUyyLWX41+1IWZz95gv5DAYv9/YIrhz1ztxPsw9tXUhReLNL0rcGhGQn+JSijRfKwwcsqk5Ne5OYO5NyIpkeeqt/XMDTz5oIftwBeb2OU09kEZGED7Vnu1aJMIXWYB6W+bMmGqCX8FVkh84iQiDgVFJnjlmrFHx+nIpDnVRzok2wixrQbpOTs4QvNeJHL1gEeWV92bahFZO8MS7plxE2UFez1kMFhUOidUnAOc98qNg4pZbluwSs5oc/G94vZX2YwTbzjbzmObbBS+Ln9kq+n46thFHQl0jY2wvghmMdBztIooBvZ9mDc2zvcJRX9ZratG/tDnWSXgrMdbQyLxcyMXm+ex4RhOzfZp6zel4y8= Content-Type: text/plain; charset="us-ascii" Content-ID: <92A3DAB23753FE40BB55EC4FF7568523@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 6931790b-a5e1-4944-e41a-08d71ab199a4 X-MS-Exchange-CrossTenant-originalarrivaltime: 06 Aug 2019 21:03:58.3629 (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: MWHPR15MB1790 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-06_10:,, 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=879 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908060182 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 6, 2019, at 3:02 AM, Oleg Nesterov wrote: >=20 > On 08/02, 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); >> + pmd_t *pmd =3D mm_find_pmd(mm, haddr); >> + struct page *hpage =3D NULL; >> + spinlock_t *ptl; >> + int count =3D 0; >> + pmd_t _pmd; >> + int i; >> + >> + if (!vma || !vma->vm_file || !pmd || >> + vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE) >> + return; >=20 > I still can't understand why is it safe to blindly use mm_find_pmd(). >=20 > Say, what pmd_offset(pud, address) will return to this function if > pud_huge() =3D=3D T? IIUC, this is possible if is_file_hugepages(vm_file)= . > How the code below can use this result? IIUC, the concern is matching files in hugetlbfs. Maybe we can exclude that specifically?=20 >=20 > I think you need something like hugepage_vma_check() or even > hugepage_vma_revalidate(). To use hugepage_vma_check(), we will need to set VM_HUGEPAGE for the=20 following case: mount shm with huge=3Dalways copy app to shm start app and enable uprobe disable uprobe This vma will not have VM_HUGEPAGE, so it will fail hugepage_vma_check(). How about something like: diff --git i/kernel/events/uprobes.c w/kernel/events/uprobes.c index 94d38a39d72e..f0d3e367f907 100644 --- i/kernel/events/uprobes.c +++ w/kernel/events/uprobes.c @@ -532,8 +532,10 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, s= truct mm_struct *mm, put_page(new_page); new_page =3D NULL; - if (PageCompound(orig_page)) + if (PageCompound(orig_page)) { orig_page_huge =3D true; + vma->vm_flags |=3D VM_HUGEPAGE; + } } put_page(orig_page); } Thanks, Song=