Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

[Logan Gunthorpe]

On 19/04/17 11:41 AM, Dan Williams wrote:
> No, not quite ;-). I still don't think we should require the non-HMM
> to pass NULL for all the HMM arguments. What I like about Logan's
> proposal is to have a separate create and register steps dev_pagemap.
> That way call paths that don't care about HMM specifics can just turn
> around and register the vanilla dev_pagemap.

Would you necessarily even need a create step? I was thinking more along
the lines that struct dev_pagemap _could_ just be a member in another
structure. The caller would set the attributes they needed and pass it
to devm_memremap. (Similar to how we commonly do things with struct
device, et al). Potentially, that could also get rid of the need for the
*data pointer HMM is using to get back the struct hmm_devmem seeing
container_of could be used instead.

>> Note i won't make any change now on that front but if it make sense
>> i am happy to do it as separate patchset on top of HMM.
>>
>> Also i don't want p2pmem to be an exclusive or with HMM, we will want
>> GPU to do peer to peer DMA and thus HMM ZONE_DEVICE pages to support
>> this too.
> 
> Yes, this makes sense I think we really just want to distinguish host
> memory or not in terms of the dev_pagemap type.

That depends though. If unaddressable memory needs different steps to
get to the DMA address (ie if it has to setup a gpu window) then we may
still need a way to distinguish the two types of non-host memory.

Logan