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Thu, 1 Aug 2019 17:37:03 +0000 Received: from MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::d4fc:70c0:79a5:f41b]) by MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::d4fc:70c0:79a5:f41b%2]) with mapi id 15.20.2115.005; Thu, 1 Aug 2019 17:37:03 +0000 From: Song Liu To: Oleg Nesterov CC: lkml , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , Kernel Team , "william.kucharski@oracle.com" , "srikar@linux.vnet.ibm.com" Subject: Re: [PATCH v2 1/2] khugepaged: enable collapse pmd for pte-mapped THP Thread-Topic: [PATCH v2 1/2] khugepaged: enable collapse pmd for pte-mapped THP Thread-Index: AQHVR86KvCEU4VHLnkGVG5f001755abmYVIAgAAuhoA= Date: Thu, 1 Aug 2019 17:37:03 +0000 Message-ID: <36D3C0F0-17CE-42B9-9661-B376D608FA7D@fb.com> References: <20190731183331.2565608-1-songliubraving@fb.com> <20190731183331.2565608-2-songliubraving@fb.com> <20190801145032.GB31538@redhat.com> In-Reply-To: <20190801145032.GB31538@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::2:33d7] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: b57bd20e-96ba-440a-ef4b-08d716a6ddb2 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1167; 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charset="us-ascii" Content-ID: <33FB7EC24D20944497C1091E287D6732@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: b57bd20e-96ba-440a-ef4b-08d716a6ddb2 X-MS-Exchange-CrossTenant-originalarrivaltime: 01 Aug 2019 17:37:03.4767 (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: MWHPR15MB1167 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_08:,, 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=646 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908010183 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Aug 1, 2019, at 7:50 AM, Oleg Nesterov wrote: >=20 > On 07/31, Song Liu wrote: >>=20 >> +static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm, >> + unsigned long addr) >> +{ >> + struct mm_slot *mm_slot; >> + int ret =3D 0; >> + >> + /* hold mmap_sem for khugepaged_test_exit() */ >> + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); >> + VM_BUG_ON(addr & ~HPAGE_PMD_MASK); >> + >> + if (unlikely(khugepaged_test_exit(mm))) >> + return 0; >> + >> + if (!test_bit(MMF_VM_HUGEPAGE, &mm->flags) && >> + !test_bit(MMF_DISABLE_THP, &mm->flags)) { >> + ret =3D __khugepaged_enter(mm); >> + if (ret) >> + return ret; >> + } >=20 > could you explain why do we need mm->mmap_sem, khugepaged_test_exit() che= ck > and __khugepaged_enter() ? If the mm doesn't have a mm_slot, we would like to create one here (by=20 calling __khugepaged_enter()).=20 This happens when the THP is created by another mm, or by tmpfs with=20 "huge=3Dalways"; and then page table of this mm got split by split_huge_pmd= ().=20 With current kernel, this happens when we attach/detach uprobe to a file=20 in tmpfs with huge=3Dalways.=20 Does this answer your question? Thanks, Song