Re: [PATCH v2 00/10] Copy Offload in NVMe Fabrics with P2P PCI Memory

Logan Gunthorpe
2018-03-02T22:24:36Z

On 02/03/18 02:44 PM, Benjamin Herrenschmidt wrote:
> Allright, so, I think I have a plan to fix this, but it will take a
> little bit of time.
>
> Basically the idea is to have firmware pass to Linux a region that's
> known to not have anything in it that it can use for the vmalloc space
> rather than have linux arbitrarily cut the address space in half.
>
> I'm pretty sure I can always find large enough "holes" in the physical
> address space that are outside of both RAM/OpenCAPI/Nvlink and
> PCIe/MMIO space. If anything, unused chip IDs. But I don't want Linux
> to have to know about the intimate HW details so I'll pass it from FW.
>
> It will take some time to adjust Linux and get updated FW around
> though.
>
> Once that's done, I'll be able to have the linear mapping go through
> the entire 52-bit space (minus that hole). Of course the hole need to
> be large enough to hold a vmemmap for a 52-bit space, so that's about
> 4TB. So I probably need a hole that's at least 8TB.
>
> As for the mapping attributes, it should be easy for my linear mapping
> code to ensure anything that isn't actual RAM is mapped NC.

Very cool. I'm glad to hear you found a way to fix this.

Thanks,

Logan