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SubjectRe: [HMM v13 00/18] HMM (Heterogeneous Memory Management) v13
John Hubbard <> writes:

> On Fri, 18 Nov 2016, Jérôme Glisse wrote:
>> Cliff note: HMM offers 2 things (each standing on its own). First
>> it allows to use device memory transparently inside any process
>> without any modifications to process program code. Second it allows
>> to mirror process address space on a device.
>> Change since v12 is the use of struct page for device memory even if
>> the device memory is not accessible by the CPU (because of limitation
>> impose by the bus between the CPU and the device).
>> Using struct page means that their are minimal changes to core mm
>> code. HMM build on top of ZONE_DEVICE to provide struct page, it
>> adds new features to ZONE_DEVICE. The first 7 patches implement
>> those changes.
>> Rest of patchset is divided into 3 features that can each be use
>> independently from one another. First is the process address space
>> mirroring (patch 9 to 13), this allow to snapshot CPU page table
>> and to keep the device page table synchronize with the CPU one.
>> Second is a new memory migration helper which allow migration of
>> a range of virtual address of a process. This memory migration
>> also allow device to use their own DMA engine to perform the copy
>> between the source memory and destination memory. This can be
>> usefull even outside HMM context in many usecase.
>> Third part of the patchset (patch 17-18) is a set of helper to
>> register a ZONE_DEVICE node and manage it. It is meant as a
>> convenient helper so that device drivers do not each have to
>> reimplement over and over the same boiler plate code.
>> I am hoping that this can now be consider for inclusion upstream.
>> Bottom line is that without HMM we can not support some of the new
>> hardware features on x86 PCIE. I do believe we need some solution
>> to support those features or we won't be able to use such hardware
>> in standard like C++17, OpenCL 3.0 and others.
>> I have been working with NVidia to bring up this feature on their
>> Pascal GPU. There are real hardware that you can buy today that
>> could benefit from HMM. We also intend to leverage this inside the
>> open source nouveau driver.
> Hi,
> We (NVIDIA engineering) have been working closely with Jerome on this for
> several years now, and I wanted to mention that NVIDIA is committed to
> using HMM. We've done initial testing of this patchset on Pascal GPUs (a
> bit more detail below) and it is looking good.

This can also be used on IBM platforms like Minsky (,32661.html

There is also discussion around using this for device accelerated page
migration. That can help with coherent device memory node work.


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