Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v8 02/14] mm/gup: check every subpage of a compound page
 during isolation
To:     Pavel Tatashin <pasha.tatashin@soleen.com>, jgg@ziepe.ca
References: <20210125194751.1275316-1-pasha.tatashin@soleen.com>
 <20210125194751.1275316-3-pasha.tatashin@soleen.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com,
        david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com,
        sashal@kernel.org, tyhicks@linux.microsoft.com,
        iamjoonsoo.kim@lge.com, mike.kravetz@oracle.com,
        rostedt@goodmis.org, mingo@redhat.com, peterz@infradead.org,
        mgorman@suse.de, willy@infradead.org, rientjes@google.com,
        jhubbard@nvidia.com, linux-doc@vger.kernel.org,
        ira.weiny@intel.com, linux-kselftest@vger.kernel.org,
        jmorris@namei.org
From:   Joao Martins <joao.m.martins@oracle.com>
Message-ID: <05a66361-214c-2afe-22e4-12862ea1e4e2@oracle.com>
Date:   Wed, 3 Feb 2021 13:22:18 +0000
In-Reply-To: <20210125194751.1275316-3-pasha.tatashin@soleen.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-MessageSentRepresentingType: 1
Received: from [192.168.1.67] (94.61.1.144) by LO2P265CA0396.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:f::24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3825.20 via Frontend Transport; Wed, 3 Feb 2021 13:22:25 +0000
X-MS-PublicTrafficType: Email
X-MS-Office365-Filtering-Correlation-Id: c41cf4f6-2233-44b3-6e6f-08d8c846c275
X-MS-TrafficTypeDiagnostic: BYAPR10MB3093:
X-MS-Exchange-Transport-Forked: True
X-Microsoft-Antispam-PRVS: <BYAPR10MB3093D9EE9BC6695367215697BBB49@BYAPR10MB3093.namprd10.prod.outlook.com>
X-MS-Oob-TLC-OOBClassifiers: OLM:9508;
X-MS-Exchange-SenderADCheck: 1
X-Microsoft-Antispam: BCL:0;
X-Microsoft-Antispam-Message-Info: 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
X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR10MB3077.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(376002)(366004)(136003)(346002)(396003)(39860400002)(66556008)(83380400001)(31686004)(26005)(66476007)(8936002)(66946007)(7416002)(6666004)(2906002)(53546011)(8676002)(36756003)(2616005)(6486002)(16576012)(16526019)(186003)(31696002)(86362001)(956004)(5660300002)(4326008)(316002)(478600001)(45980500001);DIR:OUT;SFP:1101;
X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?QWhjcytFOTZ4REJhcU1zTER2bEJCV1VlQUU2cnZjWmdkdzlPSTN6eXpKZ1pa?=
 =?utf-8?B?dU1IblVlR2gxOUJOQnp0TDZtdWdtZWZRYkdQV0kvaVlTYU9vaVAyeFQzdEVw?=
 =?utf-8?B?VjQwOHBIZWZPZ0ZTYndrWjF3bkp1NW9PcFJORkxrY1NPcmhwcHNpUDY1UEFq?=
 =?utf-8?B?MDdEQUdnOHcxVnR5NStsTGVSRWx6SGhTUDRuaklpR2ppcW5ZUWwwWmxmS1BO?=
 =?utf-8?B?TDZ5SmdiT2VvZFJncTMzblErRjJybnlyb0pCdVc1RDhuZlEvWXk4SmZOb1V6?=
 =?utf-8?B?UHNKNUNZcTdzNzRCY1VoS2xsQ0l3b0w3cWRMc0p1UFpha3dPTnRjajltb0ds?=
 =?utf-8?B?NnVwSkZnNGs1YTVqWktGbHZ6Z3F4QWV6WlplQms5bkhEMDQxSk94TnR4QlZs?=
 =?utf-8?B?Y2dVNHhjeEthTHBkSkhBYVNldXMxVmphcUNSc0xsdkUzTmk2anVDNytOaVZz?=
 =?utf-8?B?K0lIdk50d0o5V01YelVkbUMzMnJCc002aE9yUzFZVGpESWRHSVFIc3dYYmVr?=
 =?utf-8?B?cjNNdXJHci9wQlNQREttaTl6ajNyWWRhQUtZMDh1emo3UFdmVkZEVTRJTmV5?=
 =?utf-8?B?bUdSV05ZVDhIQTZ3cXc1bEtoSXlSL0lrQ3ZRUWowMVNWSVIzTWdxWWZzcjlw?=
 =?utf-8?B?cHF3K2xJWnV4MWRTN0sxa2FERlVNa2FMQVlDdFpmNzhpOVR1d29uZ2RLajB6?=
 =?utf-8?B?Q2s3ZjUzUjZiUTJJTkVCWUpxa3RvSG5IKzlVa2xZR3pIVHlJdFh1K3JSSUJo?=
 =?utf-8?B?SWFyM01ac2grbVV1TTYxdVl1YmdiVTZCVURQWDRLZG9pQlhFTTZJcXRoNG1t?=
 =?utf-8?B?azFMcGpYOXBQRXM1d2U5dWpRTmhjZ3BkclkrNC82WEErUG5HOUxROFdlZng3?=
 =?utf-8?B?Z2hRWUcrOEl4MkpFeUc0ZGxoRjUwQnlhc21KQmp3eFMwbUdRNUVBQ0ZGNFVH?=
 =?utf-8?B?MkRyYzhieFVzYjZKeHlBaXdFdGtMcDdaM0NyY2phSUxYV2U4bHNUOEhDaSt5?=
 =?utf-8?B?Z1YvM3h5ekpTODNaTlNIeE55VkhwemlOUVhMVWk0U1ZDbzBOcGs0bCtIL2hX?=
 =?utf-8?B?VSs1bG1YU0RNWE0rN0EyZGtxdGV4alRaWFdOVWV6TDVKdEdpTnhVTUJIbVBk?=
 =?utf-8?B?VUZOcjhoUEYvUVhnTE9iQkFGd0pmVE9DNVBjM2pCeU5xRURwODRrbnA4ck45?=
 =?utf-8?B?MHhPbHBFdEdJZ2MrV1Z4TFRqbUJBbjJ1YTEzSXF4dTk4Rm5zU0dDdDNTd1dl?=
 =?utf-8?B?STBJQ2lIWjJKRkRnYm9OMUdvbDU5QzdWRWttaHV4c0pONFBET25vS1pacnc3?=
 =?utf-8?B?QklJYjF1ald0ZjhRUkl6RDMzMStsMzlhdUwwTUEvSGNPZnQ4OVFyQVU5VjA1?=
 =?utf-8?B?enJHS1ViQ1pMTVhOdmRocFpvSmo5MjNWKzhQMWVQaCs3dHBwekYrOFUwY1h0?=
 =?utf-8?Q?zT1l4EQI?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: c41cf4f6-2233-44b3-6e6f-08d8c846c275
X-MS-Exchange-CrossTenant-AuthSource: BYAPR10MB3077.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Feb 2021 13:22:31.0196
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: WTWrhJRFJG3M7ysOXnKfEbQIcmysCiTlv+CzCZuUclOypSJfWbeuYgUGwkEQeAzTi/+3OoF5NgYew28oRzkM3V0W43dPY7r46YG7KL8vyt4=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR10MB3093
X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9883 signatures=668683
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 mlxscore=0
 suspectscore=0 spamscore=0 mlxlogscore=999 phishscore=0 adultscore=0
 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2009150000 definitions=main-2102030081
X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9883 signatures=668683
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 bulkscore=0 adultscore=0
 malwarescore=0 priorityscore=1501 impostorscore=0 suspectscore=0
 phishscore=0 clxscore=1011 lowpriorityscore=0 spamscore=0 mlxlogscore=999
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000
 definitions=main-2102030081
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 1/25/21 7:47 PM, Pavel Tatashin wrote:
> When pages are isolated in check_and_migrate_movable_pages() we skip
> compound number of pages at a time. However, as Jason noted, it is
> not necessary correct that pages[i] corresponds to the pages that
> we skipped. This is because it is possible that the addresses in
> this range had split_huge_pmd()/split_huge_pud(), and these functions
> do not update the compound page metadata.
> 
> The problem can be reproduced if something like this occurs:
> 
> 1. User faulted huge pages.
> 2. split_huge_pmd() was called for some reason
> 3. User has unmapped some sub-pages in the range
> 4. User tries to longterm pin the addresses.
> 
> The resulting pages[i] might end-up having pages which are not compound
> size page aligned.
> 
> Fixes: aa712399c1e8 ("mm/gup: speed up check_and_migrate_cma_pages() on huge page")
> Reported-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> ---

[...]

>  		/*
>  		 * If we get a page from the CMA zone, since we are going to
>  		 * be pinning these entries, we might as well move them out
> @@ -1599,8 +1596,6 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
>  				}
>  			}
>  		}
> -
> -		i += step;
>  	}
>  

With this, longterm gup will 'regress' for hugetlbfs e.g. from ~6k -> 32k usecs when
pinning a 16G hugetlb file.

Splitting can only occur on THP right? If so, perhaps we could retain the @step increment
for compound pages but when !is_transparent_hugepage(head) or just PageHuge(head) like:

+               if (!is_transparent_hugepage(head) && PageCompound(page))
+                       i += (compound_nr(head) - (pages[i] - head));

Or making specific to hugetlbfs:

+               if (PageHuge(head))
+                       i += (compound_nr(head) - (pages[i] - head));