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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 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 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