Re: [PATCH v5 5/6] drm/panfrost: Implement generic DRM object RSS reporting function

[Steven Price <steven.price@arm.com>]

On 18/09/2023 11:32, Boris Brezillon wrote:
> On Mon, 18 Sep 2023 11:01:43 +0100
> Steven Price <steven.price@arm.com> wrote:
> 
>> On 14/09/2023 23:38, Adrián Larumbe wrote:
>>> BO's RSS is updated every time new pages are allocated on demand and mapped
>>> for the object at GPU page fault's IRQ handler, but only for heap buffers.
>>> The reason this is unnecessary for non-heap buffers is that they are mapped
>>> onto the GPU's VA space and backed by physical memory in their entirety at
>>> BO creation time.
>>>
>>> This calculation is unnecessary for imported PRIME objects, since heap
>>> buffers cannot be exported by our driver, and the actual BO RSS size is the
>>> one reported in its attached dmabuf structure.
>>>
>>> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
>>> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>  
>>
>> Am I missing something, or are we missing a way of resetting
>> heap_rss_size when the shrinker purges? It looks like after several
>> grow/purge cycles, heap_rss_size could actually grow to be larger than
>> the BO which is clearly wrong.
> 
> Didn't even consider this case since we don't flag heap BOs purgeable
> in mesa(panfrost), but let's assume we did. If the BO is purged, I'd
> expect the core to report 0MB of resident memory anyway. And purged BOs
> are not supposed to be re-used if MADVISE(WILL_NEED) returns
> retained=false, they should be destroyed. Not 100% sure this is
> enforced everywhere though (we might actually miss tests to make sure
> users don't pass purged BOs to jobs, or make the alloc-on-fault logic
> doesn't try to grow a purged GEM).
> 
> If we want to implement transparent BO swap{out,in} (Dmitry's
> patchset), that's be a different story, and we'll indeed have to set
> heap_rss_size back to zero on eviction.

Ah, ok. So we should be safe as things stand - but this is something to
remember about in the future. Looking more closely at the code I can see
an madvise(WILL_NEED) will fail if retained=false
(drm_gem_shmem_madvise() only updates the state it shmem->madv >= 0).

In which case:

Reviewed-by: Steven Price <steven.price@arm.com>

>>
>> Steve
>>
>>> ---
>>>  drivers/gpu/drm/panfrost/panfrost_gem.c | 15 +++++++++++++++
>>>  drivers/gpu/drm/panfrost/panfrost_gem.h |  5 +++++
>>>  drivers/gpu/drm/panfrost/panfrost_mmu.c |  1 +
>>>  3 files changed, 21 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
>>> index 7d8f83d20539..4365434b48db 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
>>> @@ -208,6 +208,20 @@ static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj
>>>  	return res;
>>>  }
>>>  
>>> +static size_t panfrost_gem_rss(struct drm_gem_object *obj)
>>> +{
>>> +	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
>>> +
>>> +	if (bo->is_heap) {
>>> +		return bo->heap_rss_size;
>>> +	} else if (bo->base.pages) {
>>> +		WARN_ON(bo->heap_rss_size);
>>> +		return bo->base.base.size;
>>> +	} else {
>>> +		return 0;
>>> +	}
>>> +}
>>> +
>>>  static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>>>  	.free = panfrost_gem_free_object,
>>>  	.open = panfrost_gem_open,
>>> @@ -220,6 +234,7 @@ static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>>>  	.vunmap = drm_gem_shmem_object_vunmap,
>>>  	.mmap = drm_gem_shmem_object_mmap,
>>>  	.status = panfrost_gem_status,
>>> +	.rss = panfrost_gem_rss,
>>>  	.vm_ops = &drm_gem_shmem_vm_ops,
>>>  };
>>>  
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
>>> index ad2877eeeccd..13c0a8149c3a 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
>>> @@ -36,6 +36,11 @@ struct panfrost_gem_object {
>>>  	 */
>>>  	atomic_t gpu_usecount;
>>>  
>>> +	/*
>>> +	 * Object chunk size currently mapped onto physical memory
>>> +	 */
>>> +	size_t heap_rss_size;
>>> +
>>>  	bool noexec		:1;
>>>  	bool is_heap		:1;
>>>  };
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> index d54d4e7b2195..7b1490cdaa48 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> @@ -522,6 +522,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
>>>  		   IOMMU_WRITE | IOMMU_READ | IOMMU_NOEXEC, sgt);
>>>  
>>>  	bomapping->active = true;
>>> +	bo->heap_rss_size += SZ_2;
>>>  
>>>  	dev_dbg(pfdev->dev, "mapped page fault @ AS%d %llx", as, addr);
>>>    
>>
>