[PATCH 6/7] drm/i915/ttm, drm/ttm: Introduce a TTM i915 gem object backend

[Christian König]

Am 11.05.21 um 16:28 schrieb Thomas Hellström:
>
> On 5/11/21 4:09 PM, Christian König wrote:
>>
>>
>> Am 11.05.21 um 16:06 schrieb Thomas Hellström (Intel):
>>>
>>> On 5/11/21 3:58 PM, Christian König wrote:
>>>> Am 11.05.21 um 15:25 schrieb Thomas Hellström:
>>>>> Most logical place to introduce TTM buffer objects is as an i915
>>>>> gem object backend. We need to add some ops to account for added
>>>>> functionality like delayed delete and LRU list manipulation.
>>>>>
>>>>> Initially we support only LMEM and SYSTEM memory, but SYSTEM
>>>>> (which in this case means evicted LMEM objects) is not
>>>>> visible to i915 GEM yet. The plan is to move the i915 gem system 
>>>>> region
>>>>> over to the TTM system memory type in upcoming patches.
>>>>>
>>>>> We set up GPU bindings directly both from LMEM and from the system 
>>>>> region,
>>>>> as there is no need to use the legacy TTM_TT memory type. We reserve
>>>>> that for future porting of GGTT bindings to TTM.
>>>>>
>>>>> There are some changes to TTM to allow for purging system memory 
>>>>> buffer
>>>>> objects and to refuse swapping of some objects: Unfortunately i915 
>>>>> gem
>>>>> still relies heavily on short-term object pinning, and we've 
>>>>> chosen to
>>>>> keep short-term-pinned buffer objects on the TTM LRU lists for now,
>>>>> meaning that we need some sort of mechanism to tell TTM they are not
>>>>> swappable. A longer term goal is to get rid of the short-term 
>>>>> pinning.
>>>>
>>>> Well just use the eviction_valuable interface for this.
>>>
>>> Yes, we do that for vram/lmem eviction, but we have nothing similar 
>>> for system swapping. Do I understand you correctly that you want me 
>>> to add a call to eviction_valuable() also for that instead of 
>>> swap_possible()?
>>
>> You should already have that. eviction_valuable is called in both cases.
>>
> Hmm. I can only see it called from ttm_mem_evict_first() which is not 
> in the swapping path? Or do I miss something?

Mhm, looks like my recollection was wrong. We should probably move the 
call into the ttm_bo_evict_swapout_allowable() function.

Christian.

>
> Thanks,
>
> Thomas
>
>
>