[Intel-gfx] [PATCH] drm/i915: Avoid GPU stalls from kswapd

[Daniel Vetter]

On Fri, Jun 19, 2015 at 02:04:16PM +0100, Chris Wilson wrote:
> Exclude active GPU pages from the purview of the background shrinker
> (kswapd), as these cause uncontrollable GPU stalls. Given that the
> shrinker is rerun until the freelists are satisfied, we should have
> opportunity in subsequent passes to recover the pages once idle. If the
> machine does run out of memory entirely, we have the forced idling in the
> oom-notifier as a means of releasing all the pages we can before an oom
> is prematurely executed.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h          | 1 +
>  drivers/gpu/drm/i915/i915_gem_shrinker.c | 8 ++++++--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 71f4ca5088e2..e0dcd018379f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3185,6 +3185,7 @@ unsigned long i915_gem_shrink(struct drm_i915_private *dev_priv,
>  #define I915_SHRINK_PURGEABLE 0x1
>  #define I915_SHRINK_UNBOUND 0x2
>  #define I915_SHRINK_BOUND 0x4
> +#define I915_SHRINK_ACTIVE 0x8
>  unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv);
>  void i915_gem_shrinker_init(struct drm_i915_private *dev_priv);
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> index bd1cf921aead..8d25ec8a6559 100644
> --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> @@ -123,6 +123,10 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
>  			    obj->madv != I915_MADV_DONTNEED)
>  				continue;
>  
> +			if ((flags & I915_SHRINK_ACTIVE) == 0 &&

Isn't there a "I'm kswapd" process flag we could use to make the shrinker
a bit more clever between synchronous reclaim and kswap reclaim? Or has
synchronous reclaim died as a thing?
-Daniel

> +			    obj->active)
> +				continue;
> +
>  			drm_gem_object_reference(&obj->base);
>  
>  			/* For the unbound phase, this should be a no-op! */
> @@ -166,7 +170,7 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv)
>  	i915_gem_retire_requests(dev_priv->dev);
>  
>  	return i915_gem_shrink(dev_priv, LONG_MAX,
> -			       I915_SHRINK_BOUND | I915_SHRINK_UNBOUND);
> +			       I915_SHRINK_BOUND | I915_SHRINK_UNBOUND | I915_SHRINK_ACTIVE);
>  }
>  
>  static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
> @@ -221,7 +225,7 @@ i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
>  			count += obj->base.size >> PAGE_SHIFT;
>  
>  	list_for_each_entry(obj, &dev_priv->mm.bound_list, global_list) {
> -		if (obj->pages_pin_count == num_vma_bound(obj))
> +		if (!obj->active && obj->pages_pin_count == num_vma_bound(obj))
>  			count += obj->base.size >> PAGE_SHIFT;
>  	}
>  
> -- 
> 2.1.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch