[PATCH 8/9] drm/ttm: Don't count pages in SG BOs against pages_limit

[Christian König]

Am 14.04.21 um 12:26 schrieb Daniel Vetter:
> On Wed, Apr 14, 2021 at 11:19:41AM +0200, Christian König wrote:
>> Am 14.04.21 um 11:15 schrieb Daniel Vetter:
>>> On Wed, Apr 14, 2021 at 08:51:51AM +0200, Christian König wrote:
>>>> Am 14.04.21 um 08:48 schrieb Felix Kuehling:
>>>>> Pages in SG BOs were not allocated by TTM. So don't count them against
>>>>> TTM's pages limit.
>>>>>
>>>>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>>>
>>>> Going to pick that one up for inclusion in drm-misc-next.
>>> See my other email, but why do we need this? A bit more explanation is imo
>>> needed here at least, since we still need to guarantee that allocations
>>> don't over the limit in total for all gpu buffers together. At least until
>>> the shrinker has landed.
>>>
>>> And this here just opens up the barn door without any explanation why it's
>>> ok.
>> The SG based BOs might not even be backed by pages. E.g. exported VRAM.
>>
>> So either they are exported by a driver which should have accounted for the
>> allocation, exported by TTM which already did the accounting or doesn't even
>> point to pages at all.
>>
>> This is really a bug fix to recreate the behavior we had before moving the
>> accounting to this place.
> Throw that into the commit message and a-b: me. Ideally with a Fixes: line
> or so pointing at the offending commit that broke stuff. Commit messages
> should really go into more detail when there's an entire story behind a
> small change like this one.

Sorry I though that this would be obvious :)

I've already pushed the patch in the morning, but going to keep that in 
mind for the next time.

Christian.

> -Daniel
>
>> Christian.
>>
>>> -Daniel
>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>> ---
>>>>>     drivers/gpu/drm/ttm/ttm_tt.c | 27 ++++++++++++++++++---------
>>>>>     1 file changed, 18 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
>>>>> index 5d8820725b75..e8b8c3257392 100644
>>>>> --- a/drivers/gpu/drm/ttm/ttm_tt.c
>>>>> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
>>>>> @@ -317,9 +317,12 @@ int ttm_tt_populate(struct ttm_device *bdev,
>>>>>     	if (ttm_tt_is_populated(ttm))
>>>>>     		return 0;
>>>>> -	atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
>>>>> -	if (bdev->pool.use_dma32)
>>>>> -		atomic_long_add(ttm->num_pages, &ttm_dma32_pages_allocated);
>>>>> +	if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>>> +		atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
>>>>> +		if (bdev->pool.use_dma32)
>>>>> +			atomic_long_add(ttm->num_pages,
>>>>> +					&ttm_dma32_pages_allocated);
>>>>> +	}
>>>>>     	while (atomic_long_read(&ttm_pages_allocated) > ttm_pages_limit ||
>>>>>     	       atomic_long_read(&ttm_dma32_pages_allocated) >
>>>>> @@ -350,9 +353,12 @@ int ttm_tt_populate(struct ttm_device *bdev,
>>>>>     	return 0;
>>>>>     error:
>>>>> -	atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
>>>>> -	if (bdev->pool.use_dma32)
>>>>> -		atomic_long_sub(ttm->num_pages, &ttm_dma32_pages_allocated);
>>>>> +	if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>>> +		atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
>>>>> +		if (bdev->pool.use_dma32)
>>>>> +			atomic_long_sub(ttm->num_pages,
>>>>> +					&ttm_dma32_pages_allocated);
>>>>> +	}
>>>>>     	return ret;
>>>>>     }
>>>>>     EXPORT_SYMBOL(ttm_tt_populate);
>>>>> @@ -382,9 +388,12 @@ void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm)
>>>>>     	else
>>>>>     		ttm_pool_free(&bdev->pool, ttm);
>>>>> -	atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
>>>>> -	if (bdev->pool.use_dma32)
>>>>> -		atomic_long_sub(ttm->num_pages, &ttm_dma32_pages_allocated);
>>>>> +	if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>>> +		atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
>>>>> +		if (bdev->pool.use_dma32)
>>>>> +			atomic_long_sub(ttm->num_pages,
>>>>> +					&ttm_dma32_pages_allocated);
>>>>> +	}
>>>>>     	ttm->page_flags &= ~TTM_PAGE_FLAG_PRIV_POPULATED;
>>>>>     }
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