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Date:   Thu, 17 Jun 2021 10:56:03 -0500
From:   "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>
To:     akpm@...ux-foundation.org, Felix.Kuehling@....com,
        linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jgg@...dia.com, jglisse@...hat.com
Subject: Re: [PATCH v3 0/8] Support DEVICE_GENERIC memory in migrate_vma_*


On 6/17/2021 10:16 AM, Alex Sierra wrote:
> v1:
> AMD is building a system architecture for the Frontier supercomputer with a
> coherent interconnect between CPUs and GPUs. This hardware architecture allows
> the CPUs to coherently access GPU device memory. We have hardware in our labs
> and we are working with our partner HPE on the BIOS, firmware and software
> for delivery to the DOE.
>
> The system BIOS advertises the GPU device memory (aka VRAM) as SPM
> (special purpose memory) in the UEFI system address map. The amdgpu driver looks
> it up with lookup_resource and registers it with devmap as MEMORY_DEVICE_GENERIC
> using devm_memremap_pages.
>
> Now we're trying to migrate data to and from that memory using the migrate_vma_*
> helpers so we can support page-based migration in our unified memory allocations,
> while also supporting CPU access to those pages.
>
> This patch series makes a few changes to make MEMORY_DEVICE_GENERIC pages behave
> correctly in the migrate_vma_* helpers. We are looking for feedback about this
> approach. If we're close, what's needed to make our patches acceptable upstream?
> If we're not close, any suggestions how else to achieve what we are trying to do
> (i.e. page migration and coherent CPU access to VRAM)?
>
> This work is based on HMM and our SVM memory manager that was recently upstreamed
> to Dave Airlie's drm-next branch
> https://lore.kernel.org/dri-devel/20210527205606.2660-6-Felix.Kuehling@amd.com/T/#r996356015e295780eb50453e7dbd5d0d68b47cbc
Corrected link:

https://cgit.freedesktop.org/drm/drm/log/?h=drm-next

Regards,
Alex Sierra

> On top of that we did some rework of our VRAM management for migrations to remove
> some incorrect assumptions, allow partially successful migrations and GPU memory
> mappings that mix pages in VRAM and system memory.
> https://patchwork.kernel.org/project/dri-devel/list/?series=489811

Corrected link:

https://lore.kernel.org/dri-devel/20210527205606.2660-6-Felix.Kuehling@amd.com/T/#r996356015e295780eb50453e7dbd5d0d68b47cbc

Regards,
Alex Sierra

>
> v2:
> This patch series version has merged "[RFC PATCH v3 0/2]
> mm: remove extra ZONE_DEVICE struct page refcount" patch series made by
> Ralph Campbell. It also applies at the top of these series, our changes
> to support device generic type in migration_vma helpers.
> This has been tested in systems with device memory that has coherent
> access by CPU.
>
> Also addresses the following feedback made in v1:
> - Isolate in one patch kernel/resource.c modification, based
> on Christoph's feedback.
> - Add helpers check for generic and private type to avoid
> duplicated long lines.
>
> v3:
> - Include cover letter from v1
> - Rename dax_layout_is_idle_page func to dax_page_unused in patch
> ext4/xfs: add page refcount helper
>
> Patches 1-2 Rebased Ralph Campbell's ZONE_DEVICE page refcounting patches
> Patches 4-5 are for context to show how we are looking up the SPM
> memory and registering it with devmap.
> Patches 3,6-8 are the changes we are trying to upstream or rework to
> make them acceptable upstream.
>
> Alex Sierra (6):
>    kernel: resource: lookup_resource as exported symbol
>    drm/amdkfd: add SPM support for SVM
>    drm/amdkfd: generic type as sys mem on migration to ram
>    include/linux/mm.h: helpers to check zone device generic type
>    mm: add generic type support to migrate_vma helpers
>    mm: call pgmap->ops->page_free for DEVICE_GENERIC pages
>
> Ralph Campbell (2):
>    ext4/xfs: add page refcount helper
>    mm: remove extra ZONE_DEVICE struct page refcount
>
>   arch/powerpc/kvm/book3s_hv_uvmem.c       |  2 +-
>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 15 ++++--
>   drivers/gpu/drm/nouveau/nouveau_dmem.c   |  2 +-
>   fs/dax.c                                 |  8 +--
>   fs/ext4/inode.c                          |  5 +-
>   fs/xfs/xfs_file.c                        |  4 +-
>   include/linux/dax.h                      | 10 ++++
>   include/linux/memremap.h                 |  7 +--
>   include/linux/mm.h                       | 52 +++---------------
>   kernel/resource.c                        |  2 +-
>   lib/test_hmm.c                           |  2 +-
>   mm/internal.h                            |  8 +++
>   mm/memremap.c                            | 69 +++++++-----------------
>   mm/migrate.c                             | 13 ++---
>   mm/page_alloc.c                          |  3 ++
>   mm/swap.c                                | 45 ++--------------
>   16 files changed, 83 insertions(+), 164 deletions(-)
>

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