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DS0PR12MB8217.namprd12.prod.outlook.com (2603:10b6:8:f1::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9723.4; Thu, 12 Mar 2026 09:34:07 +0000 Received: from BN9PR12MB5259.namprd12.prod.outlook.com ([fe80::122c:cca7:c2b3:90ed]) by BN9PR12MB5259.namprd12.prod.outlook.com ([fe80::122c:cca7:c2b3:90ed%3]) with mapi id 15.20.9723.004; Thu, 12 Mar 2026 09:34:06 +0000 Message-ID: Date: Thu, 12 Mar 2026 15:03:47 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 5/6] drivers/migrate_offload: add DMA batch copy driver (dcbm) To: Gregory Price Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@kernel.org, willy@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, dave@stgolabs.net, Jonathan.Cameron@huawei.com, rkodsara@amd.com, vkoul@kernel.org, bharata@amd.com, sj@kernel.org, weixugc@google.com, dan.j.williams@intel.com, rientjes@google.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, dave.hansen@intel.com, hannes@cmpxchg.org, jhubbard@nvidia.com, peterx@redhat.com, riel@surriel.com, shakeel.butt@linux.dev, stalexan@redhat.com, tj@kernel.org, nifan.cxl@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260309120725.308854-3-shivankg@amd.com> <20260309120725.308854-14-shivankg@amd.com> Content-Language: en-US From: "Garg, Shivank" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: PN4P287CA0022.INDP287.PROD.OUTLOOK.COM (2603:1096:c01:269::12) To BN9PR12MB5259.namprd12.prod.outlook.com (2603:10b6:408:100::17) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN9PR12MB5259:EE_|DS0PR12MB8217:EE_ X-MS-Office365-Filtering-Correlation-Id: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/9/2026 11:34 PM, Gregory Price wrote: > On Mon, Mar 09, 2026 at 12:07:31PM +0000, Shivank Garg wrote: >> diff --git a/drivers/migrate_offload/Kconfig b/drivers/migrate_offload/Kconfig >> new file mode 100644 >> index 000000000000..0bbaedbae4ad >> --- /dev/null >> +++ b/drivers/migrate_offload/Kconfig >> @@ -0,0 +1,8 @@ >> +config DCBM_DMA >> + bool "DMA Core Batch Migrator" > > Should this be tri-state or is built-in the only valid state? Right, will fix this. > >> +static int setup_sg_tables(struct dma_work *work, struct list_head **src_pos, >> + struct list_head **dst_pos, int nr) >> +{ > ... snip .. >> + dev = dmaengine_get_dma_device(work->chan); >> + if (!dev) { >> + ret = -ENODEV; >> + goto err_free_dst_table; >> + } >> + ret = dma_map_sgtable(dev, work->src_sgt, DMA_TO_DEVICE, >> + DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING); >> + if (ret) >> + goto err_free_dst_table; >> + ret = dma_map_sgtable(dev, work->dst_sgt, DMA_FROM_DEVICE, >> + DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING); >> + if (ret) >> + goto err_unmap_src; >> + >> + if (work->src_sgt->nents != work->dst_sgt->nents) { >> + ret = -EINVAL; >> + goto err_unmap_dst; >> + } > > Fairly new to dma space, but I thought the dma stuff could merge pages > on iommu systems. Wouldn't this check hit fairly often? > I tested on Zen3 system (with PTDMA) across different folio sizes and didn't see this check hit in ~1000s of runs. I'll think more about this problem and discuss with IOMMU team. For now the focus of this series is the batch migration and core offload infrastructure. This is a reference driver to test the offload plumbing potential performance benefit. I'm happy to refine this once the design settles. Best regards, Shivank