[Mesa-dev] [PATCH] winsys/radeon: Unmap GPU VM address range when destroying BO

[Michel Dänzer]

On 16.06.2015 20:39, Christian König wrote:
> On 16.06.2015 10:56, Michel Dänzer wrote:
>> On 16.06.2015 17:34, Christian König wrote:
>>>
>>> What we would need to really clean that up is to make the VM mappings
>>> per GEM handle like you suggested or allow multiple mappings per BO like
>>> we did it for Amdgpu.
>> What kind of time-frame / effort do you think it would take to get that?
> 
> Doing it like Amdgpu is actually trivial to implement, we would just
> need to port the implementation back from Amdgpu. But the problem is
> that it would break the userspace ABI and some older mesa version
> wouldn't work any more because of this cause they couldn't detect any
> more that it's the same BO.
> 
> Doing the mapping per GEM handle might be an idea worth looking into,
> but I'm not sure how to approach that.

Allowing multiple mappings per BO but not tracking them per GEM handle
wouldn't solve the problem without this Mesa patch anyway, because the
kernel would remember all mappings until the BO is destroyed, right? I
think that might also indeed break older Mesa.

However, I think it should be safe to allow multiple mappings if they
are tracked per GEM handle. That should avoid this kind of problem even
with old Mesa without this patch. Not sure that's worth the effort though.


>>> Another alternative is to teach radeon_bomgr_free_va that a certain
>>> address range could be allocated to more than one handle.
>> What exactly do you have in mind for that? I don't think the winsys has
>> several representations of the same BO in the cases fixed by this patch,
>> and I'm not sure how it could account for external references.
> 
> Ah, right the BO could still be open by somebody else outside of mesa.
> 
> Since the code now looks up the BOs by VA we indeed shouldn't have any
> problems any more and your proposed solution should work fine.

Does that mean I get your Reviewed-by: or at least Acked-by: tag? :)


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer