Re: [RFC v3 8/8] virtio-blk: use BDRV_REQ_REGISTERED_BUF optimization hint

[Hanna Reitz]

On 08.07.22 06:17, Stefan Hajnoczi wrote:
> Register guest RAM using BlockRAMRegistrar and set the
> BDRV_REQ_REGISTERED_BUF flag so block drivers can optimize memory
> accesses in I/O requests.
>
> This is for vdpa-blk, vhost-user-blk, and other I/O interfaces that rely
> on DMA mapping/unmapping.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   include/hw/virtio/virtio-blk.h |  2 ++
>   hw/block/virtio-blk.c          | 13 +++++++++----
>   2 files changed, 11 insertions(+), 4 deletions(-)

Seems fair, but as said on patch 5, I’m quite wary of “register guest 
RAM”.  How can we guarantee that it won’t be too fragmented to be 
registerable with either nvme.c or blkio.c?

Hanna