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From:   Yongji Xie <xieyongji@bytedance.com>
Date:   Tue, 29 Jun 2021 14:40:59 +0800
Message-ID: <CACycT3vVhNdhtyohKJQuMXTic5m6jDjEfjzbzvp=2FJgwup8mg@mail.gmail.com>
Subject: Re: Re: [PATCH v8 00/10] Introduce VDUSE - vDPA Device in Userspace
To:     Jason Wang <jasowang@redhat.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
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On Tue, Jun 29, 2021 at 12:13 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> =E5=9C=A8 2021/6/28 =E4=B8=8B=E5=8D=886:32, Yongji Xie =E5=86=99=E9=81=93=
:
> >> 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 buff=
er.
>

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