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

[Daniel Vetter]

On Wed, Apr 14, 2021 at 02:46:20AM -0400, Felix Kuehling wrote:
> 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>

This sounds like papering over the lack of shrinker in ttm. Do we
guarantee that someone else has already accounted these buffers against
the ttm memory hard-limit anywhere? If not I think this needs to wait for
the shrinker work to get solid, since fixing the double-accounting for
this is probably not worth it.
-Daniel

> ---
>  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;
>  }
> -- 
> 2.31.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch