Re: [PATCH v4 0/1] Use HMM for ODP v4

[Jerome Glisse]

 On Mon, May 06, 2019 at 04:56:57PM -0300, Jason Gunthorpe wrote:
> On Thu, Apr 11, 2019 at 02:13:13PM -0400, jglisse@xxxxxxxxxx wrote:
> > From: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > 
> > Just fixed Kconfig and build when ODP was not enabled, other than that
> > this is the same as v3. Here is previous cover letter:
> > 
> > Git tree with all prerequisite:
> > https://cgit.freedesktop.org/~glisse/linux/log/?h=rdma-odp-hmm-v4
> > 
> > This patchset convert RDMA ODP to use HMM underneath this is motivated
> > by stronger code sharing for same feature (share virtual memory SVM or
> > Share Virtual Address SVA) and also stronger integration with mm code to
> > achieve that. It depends on HMM patchset posted for inclusion in 5.2 [2]
> > and [3].
> > 
> > It has been tested with pingpong test with -o and others flags to test
> > different size/features associated with ODP.
> > 
> > Moreover they are some features of HMM in the works like peer to peer
> > support, fast CPU page table snapshot, fast IOMMU mapping update ...
> > It will be easier for RDMA devices with ODP to leverage those if they
> > use HMM underneath.
> > 
> > Quick summary of what HMM is:
> >     HMM is a toolbox for device driver to implement software support for
> >     Share Virtual Memory (SVM). Not only it provides helpers to mirror a
> >     process address space on a device (hmm_mirror). It also provides
> >     helper to allow to use device memory to back regular valid virtual
> >     address of a process (any valid mmap that is not an mmap of a device
> >     or a DAX mapping). They are two kinds of device memory. Private memory
> >     that is not accessible to CPU because it does not have all the expected
> >     properties (this is for all PCIE devices) or public memory which can
> >     also be access by CPU without restriction (with OpenCAPI or CCIX or
> >     similar cache-coherent and atomic inter-connect).
> > 
> >     Device driver can use each of HMM tools separatly. You do not have to
> >     use all the tools it provides.
> > 
> > For RDMA device i do not expect a need to use the device memory support
> > of HMM. This device memory support is geared toward accelerator like GPU.
> > 
> > 
> > You can find a branch [1] with all the prerequisite in. This patch is on
> > top of rdma-next with the HMM patchset [2] and mmu notifier patchset [3]
> > applied on top of it.
> > 
> > [1] https://cgit.freedesktop.org/~glisse/linux/log/?h=rdma-odp-hmm-v4
> > [2] https://lkml.org/lkml/2019/4/3/1032
> > [3] https://lkml.org/lkml/2019/3/26/900
> 
> Jerome, please let me know if these dependent series are merged during
> the first week of the merge window.
> 
> This patch has been tested and could go along next week if the
> dependencies are met.
> 

So attached is a rebase on top of 5.2-rc1, i have tested with pingpong
(prefetch and not and different sizes). Seems to work ok.

Cheers,
Jérôme