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Subject: Re: [PATCH v8 00/10] Introduce VDUSE - vDPA Device in Userspace
To:     Yongji Xie <xieyongji@bytedance.com>
Cc:     Yongji Xie <elohimes@gmail.com>,
        Liu Xiaodong <xiaodong.liu@intel.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        Parav Pandit <parav@nvidia.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christian Brauner <christian.brauner@canonical.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jens Axboe <axboe@kernel.dk>, bcrl@kvack.org,
        Jonathan Corbet <corbet@lwn.net>,
        =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>,
        Dan Carpenter <dan.carpenter@oracle.com>, joro@8bytes.org,
        Greg KH <gregkh@linuxfoundation.org>,
        kvm <kvm@vger.kernel.org>, netdev@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        virtualization <virtualization@lists.linux-foundation.org>,
        iommu@lists.linux-foundation.org, songmuchun@bytedance.com,
        linux-fsdevel@vger.kernel.org
References: <20210615141331.407-1-xieyongji@bytedance.com>
 <20210628103309.GA205554@storage2.sh.intel.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <90e30d9e-5709-2a0b-0449-858eea9dfec9@redhat.com>
Date:   Tue, 29 Jun 2021 15:33:49 +0800
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在 2021/6/29 下午2:40, Yongji Xie 写道:
> On Tue, Jun 29, 2021 at 12:13 PM Jason Wang <jasowang@redhat.com> wrote:
>>
>> 在 2021/6/28 下午6:32, Yongji Xie 写道:
>>>> The large barrier is bounce-buffer mapping: SPDK requires hugepages
>>>> for NVMe over PCIe and RDMA, so take some preallcoated hugepages to
>>>> map as bounce buffer is necessary. Or it's hard to avoid an extra
>>>> memcpy from bounce-buffer to hugepage.
>>>> If you can add an option to map hugepages as bounce-buffer,
>>>> then SPDK could also be a potential user of vduse.
>>>>
>>> I think we can support registering user space memory for bounce-buffer
>>> use like XDP does. But this needs to pin the pages, so I didn't
>>> consider it in this initial version.
>>>
>> Note that userspace should be unaware of the existence of the bounce buffer.
>>
> If so, it might be hard to use umem. Because we can't use umem for
> coherent mapping which needs physical address contiguous space.
>
> Thanks,
> Yongji


We probably can use umem for memory other than the virtqueue (still via 
mmap()).

Thanks