Re: [PATCH v4 3/4] vhost-user: add shared_object msg

[Gerd Hoffmann]

On Mon, Jul 17, 2023 at 01:42:02PM +0200, Albert Esteve wrote:
> Hi Michael,
> 
> True. It may be a good idea to impose a limit in the number of entries that
> can be added to the table.
> And fail to add new entries once it reaches the limit.
> 
> Not sure what would be a good limit though. For example,
> https://www.kernel.org/doc/html/v4.9/media/uapi/v4l/vidioc-reqbufs.html#c.v4l2_requestbuffers
> does not limit the number of buffers that can be allocated simultaneously,
> it is an unsigned 32-bits value.
> However, I guess 16-bits (65535) would suffice to cover the vast majority
> of usecases. Or even lower, and
> can be adjusted later, as this API gets (more) used.

virtio-gpu does accounting on the total amount of memory (look for
'hostmem').  That is only used in case virgl is *not* used, with virgl
it is much harder to figure how much host memory is actually used.
Probably the virglrenderer library would have to implement that.

If we want apply limits to the memory used by buffers it probably makes
sense to do the same, i.e. account the total amount of memory used.
dma-bufs have a fixed size, so that should be doable without too much
trouble.  Might need some changes to the API because that'll give us a
few new possible failure modes.

take care,
  Gerd