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Mon, 24 Jun 2019 22:07:00 +0000 From: Song Liu To: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" CC: "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , "peterz@infradead.org" , "oleg@redhat.com" , "rostedt@goodmis.org" , Kernel Team , "william.kucharski@oracle.com" Subject: Re: [PATCH v6 5/6] khugepaged: enable collapse pmd for pte-mapped THP Thread-Topic: [PATCH v6 5/6] khugepaged: enable collapse pmd for pte-mapped THP Thread-Index: AQHVKYdbTu9KGYA+hEyrpX71HNVoZKarXzqA Date: Mon, 24 Jun 2019 22:06:59 +0000 Message-ID: <867149FC-1F89-4FE9-98B3-621D2F42B366@fb.com> References: <20190623054829.4018117-1-songliubraving@fb.com> <20190623054829.4018117-6-songliubraving@fb.com> In-Reply-To: <20190623054829.4018117-6-songliubraving@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: [199.201.64.134] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 4731ca80-ede4-48b6-b452-08d6f8f047e5 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1840; 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charset="us-ascii" Content-ID: <440EA5C2B4657A4DB95362F92DF168EC@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 4731ca80-ede4-48b6-b452-08d6f8f047e5 X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Jun 2019 22:07:00.0148 (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: MWHPR15MB1840 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-24_14:,, 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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906240174 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 Jun 22, 2019, at 10:48 PM, Song Liu wrote: >=20 > khugepaged needs exclusive mmap_sem to access page table. When it fails > to lock mmap_sem, the page will fault in as pte-mapped THP. As the page > is already a THP, khugepaged will not handle this pmd again. >=20 > This patch enables the khugepaged to retry retract_page_tables(). >=20 > A new flag AS_COLLAPSE_PMD is introduced to show the address_space may > contain pte-mapped THPs. When khugepaged fails to trylock the mmap_sem, > it sets AS_COLLAPSE_PMD. Then, at a later time, khugepaged will retry > compound pages in this address_space. >=20 > Since collapse may happen at an later time, some pages may already fault > in. To handle these pages properly, it is necessary to prepare the pmd > before collapsing. prepare_pmd_for_collapse() is introduced to prepare > the pmd by removing rmap, adjusting refcount and mm_counter. >=20 > prepare_pmd_for_collapse() also double checks whether all ptes in this > pmd are mapping to the same THP. This is necessary because some subpage > of the THP may be replaced, for example by uprobe. In such cases, it > is not possible to collapse the pmd, so we fall back. >=20 > Signed-off-by: Song Liu > --- > include/linux/pagemap.h | 1 + > mm/khugepaged.c | 69 +++++++++++++++++++++++++++++++++++------ > 2 files changed, 60 insertions(+), 10 deletions(-) >=20 > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 9ec3544baee2..eac881de2a46 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -29,6 +29,7 @@ enum mapping_flags { > AS_EXITING =3D 4, /* final truncate in progress */ > /* writeback related tags are not used */ > AS_NO_WRITEBACK_TAGS =3D 5, > + AS_COLLAPSE_PMD =3D 6, /* try collapse pmd for THP */ > }; >=20 > /** > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index a4f90a1b06f5..9b980327fd9b 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1254,7 +1254,47 @@ static void collect_mm_slot(struct mm_slot *mm_slo= t) > } >=20 > #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE) > -static void retract_page_tables(struct address_space *mapping, pgoff_t p= goff) > + > +/* return whether the pmd is ready for collapse */ > +bool prepare_pmd_for_collapse(struct vm_area_struct *vma, pgoff_t pgoff, > + struct page *hpage, pmd_t *pmd) kbuild test robot reported I missed "static" here. But I am holding off a=20 newer version that just fixes this.=20 Thanks,=20 Song