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Wed, 18 Aug 2021 00:35:24 +0000 Subject: Re: [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page refcount To: Ralph Campbell , Alex Sierra , akpm@linux-foundation.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, hch@lst.de, jgg@nvidia.com, jglisse@redhat.com References: <20210813063150.2938-1-alex.sierra@amd.com> <20210813063150.2938-3-alex.sierra@amd.com> <7b821150-af18-f786-e419-ec245b8cfb1e@nvidia.com> From: Felix Kuehling Message-ID: <393e9815-838d-5fe6-d6ab-bfe7b543fef6@amd.com> Date: Tue, 17 Aug 2021 20:35:22 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: <7b821150-af18-f786-e419-ec245b8cfb1e@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-ClientProxiedBy: YT3PR01CA0025.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:86::29) To BN9PR12MB5129.namprd12.prod.outlook.com (2603:10b6:408:136::12) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.100] (142.186.47.3) by YT3PR01CA0025.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:86::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4436.19 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?aDRrS0Q5elBLUUtHMDM4aHI3RWFDdkpZODhzQnphWmIzZjFLYXRNbi9ONXN5?= =?utf-8?B?bGIwWVdaWkRwazc3b2s3TG9BWlVYQmptditKUHFWL0RCbUg2MWdqM3N2ajBw?= =?utf-8?B?OGRGcHdtQkJXWGtLbE43NGF6T3gza0VQUEkveTNFV0Z3ZlVCQnpYOUJMaHNt?= =?utf-8?B?RGNRTlp0VUZPM29Va2xwZVZaVXRRMHhvN3Y1MDlSQlJJUlZhY3AreTlTa0dN?= =?utf-8?B?SUxkV3hwNlkwNEtZZ2M1Vm92SjNPZStNL1dBTVZObjFRUkJOT3Uxek15aENW?= =?utf-8?B?bXdzeW5mTjduRFc3d3Jna29CSnZMZnNoTWdsd2I1NTRhOTNCSElYdzN0bThm?= =?utf-8?B?bGVYUDQ3R3k4QWFGdWw2ZEFnZnRFd004OG8xeUNOU0NsQlV1d2l5dGNOYkdo?= =?utf-8?B?SVF5NjRYOUpMWDRNaWFZTVZzdWlzSzlvaFdkS0lhV1lUR2RkbUVIcU80MmpM?= =?utf-8?B?SldGNWI5ZjlhbVdaV2gxM3c0Vm90aVV5TE9wMlZsYU1JYjVxOUxUUnYwTmhY?= =?utf-8?B?MFVKWlRDak9hcmRVYUY5aXpOVjl0ZHY1bVFOQXhicWRzU044anhYNVR1dHdZ?= =?utf-8?B?VThUTmlsU1FBcXQ1ekFaM0k2MVpybjdXUkdFbUZ6cXdFeW5YeGc4NllsWEU3?= =?utf-8?B?TUR3RVBPWXdPTjJFZkZBR3hQRStUa29CZVlXQUtDaEpIMmZGR0ZVWHVvUlNz?= =?utf-8?B?Z1F4ZFVDUGNKZ0tRaVo4Z1RlMHpKTThVUiswN3RWQXFCbFl0czNrQ2dXOVNj?= =?utf-8?B?aW1TVTJmRFlpbnRFdTYyeEhxdFM1V0xoUE1wMmMyYVgydFpwSGtqSGNnT3dz?= =?utf-8?B?RXh1Q3RFa1VwU0xmeHRYcXJmR1VEMXQ3ZS84T1YwaFJ6dWRnd3kyQzF1YW1p?= =?utf-8?B?RXlnYUJpaEFoNFNzMXp5MFJoamxIVTQzSUtjZS90M1V2R1IzeEhVc0o2SGVl?= =?utf-8?B?ZDhTNGxxc1lOVndTMzUzcEZPeUx3WGY0a0d1eGpFVWpTL2JlOWFZNllrNDkz?= =?utf-8?B?VkJPalRHNFVneWpoYmJEZ0RNTWY2d3pHK2JOSTZ6a2NBQ1NKYlZDdlhyTHhv?= =?utf-8?B?NTJwWTRPVUpkY1BKbHVycGFKR2tNcXpuU3JtSW13TEJnVGFnbkp2YzFtVnJv?= =?utf-8?B?ZEt1ZUFCOWdJd0hTYUJXbTZvN2ZzRis5NXlkRFM1ZlpRbEJjamVHanlWQzY5?= =?utf-8?B?NFgwYUh6QTNORGFmUkJvMWlkRE5pT1pxajBQVk1nU3lqeHhCMmFlLytHNEx4?= =?utf-8?B?K09WdjYzcW9uakFwRlRldXhSbjZwUzhjUEpxUGd0dzNZNG91b1FpWWZzSkhY?= =?utf-8?B?bkZRcnlHWmUwNU0wdzVxbGlhdUcwb050N0JMa25saUtEQkdubHF0STd5RW9v?= =?utf-8?B?S1UwckFaQUxSQlZrU1l5clptL2t2QWlnTkFDMHljQnM2ZWk4T25hTWtWRVN3?= =?utf-8?B?QndySjZrSmN4N3p1ZC9EWTdWdTFxVllNTGZNS0dzaGFhTHFHRHZ0MmxESHRC?= =?utf-8?B?ZVc2V3JPUGx6SzIwR245NjBXZFc2SEkyT3NHeXBsUXZuZFluTHIyS3dHVEN1?= =?utf-8?B?cmdHdnFzVXAvWHdXbWtlS3NEa29Dci9oaUdqc3h3eVB5WFVNdzNLeVJ6M1pZ?= =?utf-8?B?TmxtbXVxUXFDNXFPaHEwNEpqNFM2ZFBkZDRSMWQxeitvNjVwUlE0M2pKcGNa?= =?utf-8?B?eUlHUUlCWExaMVROSHBHdjBFS0Y5NmdiaUFJcy9tR2pMV05xZEg3UmhPU0xF?= =?utf-8?Q?ormf2GUV8NSetp4L2zOCqsCpIsHtDkfu4URjPqf?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1d8e2769-2812-4023-9c68-08d961e01194 X-MS-Exchange-CrossTenant-AuthSource: BN9PR12MB5129.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Aug 2021 00:35:24.5893 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: +kWSSSsw8drnbwIwcjGLROjNj/5eLrNwYQEQf/s1r5100GjIHM7eX6x6dvU/ZPCNPCeKybYxLzkXUudFlcgkig== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR12MB5180 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org Am 2021-08-17 um 8:01 p.m. schrieb Ralph Campbell: > On 8/12/21 11:31 PM, Alex Sierra wrote: >> From: Ralph Campbell >> >> ZONE_DEVICE struct pages have an extra reference count that >> complicates the >> code for put_page() and several places in the kernel that need to >> check the >> reference count to see that a page is not being used (gup, compaction, >> migration, etc.). Clean up the code so the reference count doesn't >> need to >> be treated specially for ZONE_DEVICE. >> >> v2: >> AS: merged this patch in linux 5.11 version >> >> v5: >> AS: add condition at try_grab_page to check for the zone device type, >> while >> page ref counter is checked less/equal to zero. In case of device >> zone, pages >> ref counter are initialized to zero. >> >> Signed-off-by: Ralph Campbell >> Signed-off-by: Alex Sierra >> --- >>   arch/powerpc/kvm/book3s_hv_uvmem.c     |  2 +- >>   drivers/gpu/drm/nouveau/nouveau_dmem.c |  2 +- >>   fs/dax.c                               |  4 +- >>   include/linux/dax.h                    |  2 +- >>   include/linux/memremap.h               |  7 +-- >>   include/linux/mm.h                     | 13 +---- >>   lib/test_hmm.c                         |  2 +- >>   mm/internal.h                          |  8 +++ >>   mm/memremap.c                          | 68 +++++++------------------- >>   mm/migrate.c                           |  5 -- >>   mm/page_alloc.c                        |  3 ++ >>   mm/swap.c                              | 45 ++--------------- >>   12 files changed, 46 insertions(+), 115 deletions(-) >> > I haven't seen a response to the issues I raised back at v3 of this > series. > https://lore.kernel.org/linux-mm/4f6dd918-d79b-1aa7-3a4c-caa67ddc29bc@nvidia.com/ > > > Did I miss something? I think part of the response was that we did more testing. Alex added support for DEVICE_GENERIC pages to test_hmm and he ran DAX tests recommended by Theodore Tso. In that testing he ran into a WARN_ON_ONCE about a zero page refcount in try_get_page. The fix is in the latest version of patch 2. But it's already obsolete because John Hubbard is about to remove that function altogether. I think the issues you raised were more uncertainty than known bugs. It seems the fact that you can have DAX pages with 0 refcount is a feature more than a bug. 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dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=amd.com; Received: from BN9PR12MB5129.namprd12.prod.outlook.com (2603:10b6:408:136::12) by BN9PR12MB5180.namprd12.prod.outlook.com (2603:10b6:408:11d::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4415.17; Wed, 18 Aug 2021 00:35:24 +0000 Received: from BN9PR12MB5129.namprd12.prod.outlook.com ([fe80::b891:a906:28f0:fdb]) by BN9PR12MB5129.namprd12.prod.outlook.com ([fe80::b891:a906:28f0:fdb%4]) with mapi id 15.20.4415.023; Wed, 18 Aug 2021 00:35:24 +0000 Subject: Re: [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page refcount To: Ralph Campbell , Alex Sierra , akpm@linux-foundation.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, hch@lst.de, jgg@nvidia.com, jglisse@redhat.com References: <20210813063150.2938-1-alex.sierra@amd.com> <20210813063150.2938-3-alex.sierra@amd.com> <7b821150-af18-f786-e419-ec245b8cfb1e@nvidia.com> From: Felix Kuehling Message-ID: <393e9815-838d-5fe6-d6ab-bfe7b543fef6@amd.com> Date: Tue, 17 Aug 2021 20:35:22 -0400 User-Agent: Mozilla/5.0 (X11; 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Clean up the code so the reference count doesn't >> need to >> be treated specially for ZONE_DEVICE. >> >> v2: >> AS: merged this patch in linux 5.11 version >> >> v5: >> AS: add condition at try_grab_page to check for the zone device type, >> while >> page ref counter is checked less/equal to zero. In case of device >> zone, pages >> ref counter are initialized to zero. >> >> Signed-off-by: Ralph Campbell >> Signed-off-by: Alex Sierra >> --- >>   arch/powerpc/kvm/book3s_hv_uvmem.c     |  2 +- >>   drivers/gpu/drm/nouveau/nouveau_dmem.c |  2 +- >>   fs/dax.c                               |  4 +- >>   include/linux/dax.h                    |  2 +- >>   include/linux/memremap.h               |  7 +-- >>   include/linux/mm.h                     | 13 +---- >>   lib/test_hmm.c                         |  2 +- >>   mm/internal.h                          |  8 +++ >>   mm/memremap.c                          | 68 +++++++------------------- >>   mm/migrate.c                           |  5 -- >>   mm/page_alloc.c                        |  3 ++ >>   mm/swap.c                              | 45 ++--------------- >>   12 files changed, 46 insertions(+), 115 deletions(-) >> > I haven't seen a response to the issues I raised back at v3 of this > series. > https://lore.kernel.org/linux-mm/4f6dd918-d79b-1aa7-3a4c-caa67ddc29bc@nvidia.com/ > > > Did I miss something? I think part of the response was that we did more testing. Alex added support for DEVICE_GENERIC pages to test_hmm and he ran DAX tests recommended by Theodore Tso. In that testing he ran into a WARN_ON_ONCE about a zero page refcount in try_get_page. The fix is in the latest version of patch 2. But it's already obsolete because John Hubbard is about to remove that function altogether. I think the issues you raised were more uncertainty than known bugs. It seems the fact that you can have DAX pages with 0 refcount is a feature more than a bug. Regards,   Felix