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Tue, 13 Aug 2019 14:44:40 +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" , Johannes Weiner , "Kirill A. Shutemov" 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: AQHVTXlDuUiBx4u3AUqTmiQ0C68ad6bxcvOAgAAJMACAAXXfAIAAEp4AgAAZUACABFVTAIAAE+cAgAAVvICAAGtUAIABKBiA Date: Tue, 13 Aug 2019 14:44:40 +0000 Message-ID: <857DA509-D891-4F4C-A55C-EE58BC2CC452@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> <20190812121144.f46abvpg6lvxwwzs@box> <20190812132257.GB31560@redhat.com> <20190812144045.tkvipsyit3nccvuk@box> <2D11C742-BB7E-4296-9E97-5114FA58474B@fb.com> In-Reply-To: <2D11C742-BB7E-4296-9E97-5114FA58474B@fb.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::b9f9] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 39b36ae0-ec90-480f-8079-08d71ffcc58b x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1312; x-ms-traffictypediagnostic: MWHPR15MB1312: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; x-forefront-prvs: 01283822F8 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(39860400002)(376002)(366004)(396003)(136003)(346002)(189003)(199004)(33656002)(53546011)(102836004)(46003)(6436002)(476003)(305945005)(2616005)(11346002)(53936002)(54906003)(229853002)(186003)(6506007)(76176011)(14454004)(6916009)(86362001)(99286004)(66946007)(6486002)(478600001)(446003)(2906002)(6116002)(57306001)(6512007)(316002)(486006)(256004)(14444005)(36756003)(5660300002)(6246003)(7416002)(81156014)(5024004)(71190400001)(66446008)(64756008)(8936002)(71200400001)(4326008)(25786009)(50226002)(8676002)(76116006)(81166006)(66476007)(66556008)(7736002);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1312;H:MWHPR15MB1165.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;MX:1;A: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: 6bCzqwWa4tBAMPh3N9kK6BiQJuzOPSwERYvtyzhtOSNYKMdRXFmfb+8Z+xmVjlpkpcMd9EGwERShEbyLh5iUjLk+QHFwB3ZTRJqsDK3kLEeHdOqNti/oE6+c4xhMDq1OU6J4hkYo7jUGv6SPdP3oPepvKkZWWCBi7H95pCsLPTsZ7dvn0vMNcYAxO/3eRhRipK2C0GmE8bg3TI5E5SFAPgtf3V8aEWipuKW+I0jN8PmyXIk16zamXEiTVELy1AIWBX6i+qnGTkI0fymdfsuBpnChJc2CiV30LxUmk6H37zl2m3I1LhKPHRiwhkdk3lpma9q/RpGIV4NFKAEuFE1wb4FQAAuhRYFdSDNzFptrV8b+P1jmaR5AGxUu+fz/U1ObDSO1P+BJT/nM4mJzhdHIMZECyxnHpJyYQ9OZ0TWhJo4= Content-Type: text/plain; charset="us-ascii" Content-ID: <9FB0981101AC8245A04EE324AAD61837@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 39b36ae0-ec90-480f-8079-08d71ffcc58b X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Aug 2019 14:44:40.0299 (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: oMfXHxipdLeSMNkpJ385Kd5lgC7X6CMX/ofJAFeyebDnASkq9EM3GvvgRLRWXIRnPVLTzbn8GJvj71+vTqqQgg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1312 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-13_05:,, 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=680 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908130156 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: Hi Oleg, > On Aug 12, 2019, at 2:04 PM, Song Liu wrote: >=20 >=20 >=20 >> On Aug 12, 2019, at 7:40 AM, Kirill A. Shutemov w= rote: >>=20 >> On Mon, Aug 12, 2019 at 03:22:58PM +0200, Oleg Nesterov wrote: >>> On 08/12, Kirill A. Shutemov wrote: >>>>=20 >>>> On Fri, Aug 09, 2019 at 06:01:18PM +0000, Song Liu wrote: >>>>> + if (pte_none(*pte) || !pte_present(*pte)) >>>>> + continue; >>>>=20 >>>> You don't need to check both. Present is never none. >>>=20 >>> Agreed. >>>=20 >>> Kirill, while you are here, shouldn't retract_page_tables() check >>> vma->anon_vma (and probably do mm_find_pmd) under vm_mm->mmap_sem? >>>=20 >>> Can't it race with, say, do_cow_fault? >>=20 >> vma->anon_vma can race, but it doesn't matter. False-negative is fine. >> It's attempt to avoid taking mmap_sem where it can be not productive. >>=20 >> mm_find_pmd() cannot race with do_cow_fault() since the page is locked. >> __do_fault() has to return locked page before we touch page tables. >> It is somewhat subtle, but I wanted to avoid taking mmap_sem where it is >> possible. >>=20 >> --=20 >> Kirill A. Shutemov >=20 > Updated version attached.=20 >=20 >=20 > Besides feedbacks from Oleg and Kirill, I also revise the locking in=20 > collapse_pte_mapped_thp(): use pte_offset_map_lock() for the two loops=20 > to cover highmem. zap_pte_range() has similar use of the lock.=20 >=20 > This change is suggested by Johannes.=20 >=20 Do you have further comments for the version below? If not, could you please reply with your Acked-by or Reviewed-by? Thanks, Song >=20 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 8< =3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > From 3d931bc4780abb6109fe478a4b1a0004ce81efe1 Mon Sep 17 00:00:00 2001 > From: Song Liu > Date: Sun, 28 Jul 2019 03:43:48 -0700 > Subject: [PATCH 5/6] khugepaged: enable collapse pmd for pte-mapped THP >=20 [...]=