[RFC PATCH 0/3] Propose new struct drm_mem_region

[Brian Welty]

On 7/30/2019 3:45 AM, Daniel Vetter wrote:
> On Tue, Jul 30, 2019 at 12:24 PM Koenig, Christian
> <Christian.Koenig at amd.com> wrote:
>>
>> Am 30.07.19 um 11:38 schrieb Daniel Vetter:
>>> On Tue, Jul 30, 2019 at 08:45:57AM +0000, Koenig, Christian wrote:

Snipped the feedback on struct drm_mem_region.
Will be easier to have separate thread.

>>>>
>>>>> +/*
>>>>> + * Memory types for drm_mem_region
>>>>> + */
>>>> #define DRM_MEM_SWAP    ?
>>> btw what did you have in mind for this? Since we use shmem we kinda don't
>>> know whether the BO is actually swapped out or not, at least on the i915
>>> side. So this would be more NOT_CURRENTLY_PINNED_AND_POSSIBLY_SWAPPED_OUT.
>>
>> Yeah, the problem is not everybody can use shmem. For some use cases you
>> have to use memory allocated through dma_alloc_coherent().
>>
>> So to be able to swap this out you need a separate domain to copy it
>> from whatever is backing it currently to shmem.
>>
>> So we essentially have:
>> DRM_MEM_SYS_SWAPABLE
>> DRM_MEM_SYS_NOT_GPU_MAPPED
>> DRM_MEM_SYS_GPU_MAPPED
>>
>> Or something like that.
> 
> Yeah i915-gem is similar. We oportunistically keep the pages pinned
> sometimes even if not currently mapped into the (what ttm calls) TT.
> So I think these three for system memory make sense for us too. I
> think that's similar (at least in spirit) to the dma_alloc cache you
> have going on. Mabye instead of the somewhat cumbersome NOT_GPU_MAPPED
> we could have something like PINNED or so. Although it's not
> permanently pinned, so maybe that's confusing too.
> 

Okay, I see now I was far off the mark with what I thought TTM_PL_SYSTEM
was.  The discussion helped clear up several bits of confusion on my part.
>From proposed names, I find MAPPED and PINNED slightly confusing.
In terms of backing store description, maybe these are a little better:
  DRM_MEM_SYS_UNTRANSLATED  (TTM_PL_SYSTEM)
  DRM_MEM_SYS_TRANSLATED    (TTM_PL_TT or i915's SYSTEM)

Are these allowed to be both overlapping? Or non-overlapping (partitioned)?
Per Christian's point about removing .start, seems it doesn't need to
matter.

Whatever we define for these sub-types, does it make sense for SYSTEM and
VRAM to each have them defined?

I'm unclear how DRM_MEM_SWAP (or DRM_MEM_SYS_SWAPABLE) would get
configured by driver...  this is a fixed size partition of host memory?
Or it is a kind of dummy memory region just for swap implementation?


>>>> TTM was clearly missing that resulting in a whole bunch of extra
>>>> handling and rather complicated handling.
>>>>
>>>>> +#define DRM_MEM_SYSTEM     0
>>>>> +#define DRM_MEM_STOLEN     1
>>>> I think we need a better naming for that.
>>>>
>>>> STOLEN sounds way to much like stolen VRAM for integrated GPUs, but at
>>>> least for TTM this is the system memory currently GPU accessible.
>>> Yup this is wrong, for i915 we use this as stolen, for ttm it's the gpu
>>> translation table window into system memory. Not the same thing at all.
>>
>> Thought so. The closest I have in mind is GTT, but everything else works
>> as well.
> 
> Would your GPU_MAPPED above work for TT? I think we'll also need
> STOLEN, I'm even hearing noises that there's going to be stolen for
> discrete vram for us ... Also if we expand I guess we need to teach
> ttm to cope with more, or maybe treat the DRM one as some kind of
> sub-flavour.
Daniel, maybe what i915 calls stolen could just be DRM_MEM_RESERVED or
DRM_MEM_PRIV.  Or maybe can argue it falls into UNTRANSLATED type that
I suggested above, I'm not sure.

-Brian


> -Daniel
> 
>>
>> Christian.
>>
>>> -Daniel
>>>
>>>>
>>>> Thanks for looking into that,
>>>> Christian.
>>>>
>>>> Am 30.07.19 um 02:32 schrieb Brian Welty:
>>>>> [ By request, resending to include amd-gfx + intel-gfx.  Since resending,
>>>>>     I fixed the nit with ordering of header includes that Sam noted. ]
>>>>>
>>>>> This RFC series is first implementation of some ideas expressed
>>>>> earlier on dri-devel [1].
>>>>>
>>>>> Some of the goals (open for much debate) are:
>>>>>     - Create common base structure (subclass) for memory regions (patch #1)
>>>>>     - Create common memory region types (patch #2)
>>>>>     - Create common set of memory_region function callbacks (based on
>>>>>       ttm_mem_type_manager_funcs and intel_memory_regions_ops)
>>>>>     - Create common helpers that operate on drm_mem_region to be leveraged
>>>>>       by both TTM drivers and i915, reducing code duplication
>>>>>     - Above might start with refactoring ttm_bo_manager.c as these are
>>>>>       helpers for using drm_mm's range allocator and could be made to
>>>>>       operate on DRM structures instead of TTM ones.
>>>>>     - Larger goal might be to make LRU management of GEM objects common, and
>>>>>       migrate those fields into drm_mem_region and drm_gem_object strucures.
>>>>>
>>>>> Patches 1-2 implement the proposed struct drm_mem_region and adds
>>>>> associated common set of definitions for memory region type.
>>>>>
>>>>> Patch #3 is update to i915 and is based upon another series which is
>>>>> in progress to add vram support to i915 [2].
>>>>>
>>>>> [1] https://lists.freedesktop.org/archives/dri-devel/2019-June/224501.html
>>>>> [2] https://lists.freedesktop.org/archives/intel-gfx/2019-June/203649.html
>>>>>
>>>>> Brian Welty (3):
>>>>>     drm: introduce new struct drm_mem_region
>>>>>     drm: Introduce DRM_MEM defines for specifying type of drm_mem_region
>>>>>     drm/i915: Update intel_memory_region to use nested drm_mem_region
>>>>>
>>>>>    drivers/gpu/drm/i915/gem/i915_gem_object.c    |  2 +-
>>>>>    drivers/gpu/drm/i915/gem/i915_gem_shmem.c     |  2 +-
>>>>>    drivers/gpu/drm/i915/i915_gem_gtt.c           | 10 ++---
>>>>>    drivers/gpu/drm/i915/i915_gpu_error.c         |  2 +-
>>>>>    drivers/gpu/drm/i915/i915_query.c             |  2 +-
>>>>>    drivers/gpu/drm/i915/intel_memory_region.c    | 10 +++--
>>>>>    drivers/gpu/drm/i915/intel_memory_region.h    | 19 +++------
>>>>>    drivers/gpu/drm/i915/intel_region_lmem.c      | 26 ++++++-------
>>>>>    .../drm/i915/selftests/intel_memory_region.c  |  8 ++--
>>>>>    drivers/gpu/drm/ttm/ttm_bo.c                  | 34 +++++++++-------
>>>>>    drivers/gpu/drm/ttm/ttm_bo_manager.c          | 14 +++----
>>>>>    drivers/gpu/drm/ttm/ttm_bo_util.c             | 11 +++---
>>>>>    drivers/gpu/drm/vmwgfx/vmwgfx_gmrid_manager.c |  8 ++--
>>>>>    drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c    |  4 +-
>>>>>    include/drm/drm_mm.h                          | 39 ++++++++++++++++++-
>>>>>    include/drm/ttm/ttm_bo_api.h                  |  2 +-
>>>>>    include/drm/ttm/ttm_bo_driver.h               | 16 ++++----
>>>>>    include/drm/ttm/ttm_placement.h               |  8 ++--
>>>>>    18 files changed, 124 insertions(+), 93 deletions(-)
>>>>>
>>
> 
>