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Fri, 9 Aug 2019 16:50:27 +0000 From: Song Liu To: Oleg Nesterov CC: Linux Kernel Mailing List , Linux MM , "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 v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD Thread-Topic: [PATCH v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD Thread-Index: AQHVTXk1mNBIE/jl/kWGntKwDXuhGKbxdEOAgAAKuICAAYcWAIAABBIA Date: Fri, 9 Aug 2019 16:50:27 +0000 Message-ID: <4193FF07-3191-45D1-9F3E-90F08945389F@fb.com> References: <20190807233729.3899352-1-songliubraving@fb.com> <20190807233729.3899352-4-songliubraving@fb.com> <20190808163745.GC7934@redhat.com> <48316E06-10B2-439C-AD10-3EC8C86C259C@fb.com> <20190809163551.GB21489@redhat.com> In-Reply-To: <20190809163551.GB21489@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::1:68ef] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 58c7bd01-5570-4ad0-87a3-08d71ce9ae86 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1278; 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charset="us-ascii" Content-ID: <70C0E4356A74DB439318F9359B85B812@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 58c7bd01-5570-4ad0-87a3-08d71ce9ae86 X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Aug 2019 16:50:27.4655 (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: DITPPfoeUMhhlfNkCjtfTziI3ptcuAFybei6FUxVh0D+v8dNzjbhyG5C7jmRm36WjCEx6fFNKVnt5pM85Z/vIw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1278 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-09_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=886 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908090165 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 9, 2019, at 9:35 AM, Oleg Nesterov wrote: >=20 > On 08/08, Song Liu wrote: >>=20 >>> On Aug 8, 2019, at 9:37 AM, Oleg Nesterov wrote: >>>=20 >>> On 08/07, Song Liu wrote: >>>>=20 >>>> @@ -399,7 +399,7 @@ static struct page *follow_pmd_mask(struct vm_area= _struct *vma, >>>> spin_unlock(ptl); >>>> return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); >>>> } >>>> - if (flags & FOLL_SPLIT) { >>>> + if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) { >>>> int ret; >>>> page =3D pmd_page(*pmd); >>>> if (is_huge_zero_page(page)) { >>>> @@ -408,7 +408,7 @@ static struct page *follow_pmd_mask(struct vm_area= _struct *vma, >>>> split_huge_pmd(vma, pmd, address); >>>> if (pmd_trans_unstable(pmd)) >>>> ret =3D -EBUSY; >>>> - } else { >>>> + } else if (flags & FOLL_SPLIT) { >>>> if (unlikely(!try_get_page(page))) { >>>> spin_unlock(ptl); >>>> return ERR_PTR(-ENOMEM); >>>> @@ -420,6 +420,10 @@ static struct page *follow_pmd_mask(struct vm_are= a_struct *vma, >>>> put_page(page); >>>> if (pmd_none(*pmd)) >>>> return no_page_table(vma, flags); >>>> + } else { /* flags & FOLL_SPLIT_PMD */ >>>> + spin_unlock(ptl); >>>> + split_huge_pmd(vma, pmd, address); >>>> + ret =3D pte_alloc(mm, pmd) ? -ENOMEM : 0; >>>> } >>>=20 >>> Can't resist, let me repeat that I do not like this patch because imo >>> it complicates this code for no reason. >>=20 >> Personally, I don't think this is more complicated than your version. >=20 > I do, but of course this is subjective. >=20 >> Also, if some code calls follow_pmd_mask() with flags contains both >> FOLL_SPLIT and FOLL_SPLIT_PMD, we should honor FOLL_SPLIT and split the >> huge page. >=20 > Heh. why not other way around? Because FOLL_SPLIT splits both the page and the pmd. FOLL_SPLIT_PMD=20 only splits the pmd, so it is a subset of FOLL_SPLIT. When the user sets both, we should split both the page and the pmd.=20 Thanks, Song