linux-kernel - Re: Re: [PATCH v8 00/10] Introduce VDUSE

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Date:   Tue, 29 Jun 2021 14:40:59 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Yongji Xie <elohimes@...il.com>,
        Liu Xiaodong <xiaodong.liu@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>, joro@...tes.org,
        Greg KH <gregkh@...uxfoundation.org>,
        kvm <kvm@...r.kernel.org>, netdev@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        iommu@...ts.linux-foundation.org, songmuchun@...edance.com,
        linux-fsdevel@...r.kernel.org
Subject: Re: Re: [PATCH v8 00/10] Introduce VDUSE - vDPA Device in Userspace

On Tue, Jun 29, 2021 at 12:13 PM Jason Wang <jasowang@...hat.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