[Intel-gfx] [PATCH 10/28] drm/i915: Change shrink ordering to use locking around unbinding.

[Matthew Auld]

On Thu, 21 Oct 2021 at 11:37, Maarten Lankhorst
<maarten.lankhorst at linux.intel.com> wrote:
>
> Call drop_pages with the gem object lock held, instead of the other
> way around. This will allow us to drop the vma bindings with the
> gem object lock held.
>
> We plan to require the object lock for unpinning in the future,
> and this is an easy target.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 42 ++++++++++----------
>  1 file changed, 22 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> index af3eb7fd951d..d3f29a66cb36 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> @@ -36,8 +36,8 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
>         return swap_available() || obj->mm.madv == I915_MADV_DONTNEED;
>  }
>
> -static bool unsafe_drop_pages(struct drm_i915_gem_object *obj,
> -                             unsigned long shrink, bool trylock_vm)
> +static int drop_pages(struct drm_i915_gem_object *obj,
> +                      unsigned long shrink, bool trylock_vm)
>  {
>         unsigned long flags;
>
> @@ -208,26 +208,28 @@ i915_gem_shrink(struct i915_gem_ww_ctx *ww,
>
>                         spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
>
> -                       err = 0;
> -                       if (unsafe_drop_pages(obj, shrink, trylock_vm)) {
> -                               /* May arrive from get_pages on another bo */
> -                               if (!ww) {
> -                                       if (!i915_gem_object_trylock(obj))
> -                                               goto skip;
> -                               } else {
> -                                       err = i915_gem_object_lock(obj, ww);
> -                                       if (err)
> -                                               goto skip;
> -                               }
> -
> -                               if (!__i915_gem_object_put_pages(obj)) {
> -                                       try_to_writeback(obj, shrink);
> -                                       count += obj->base.size >> PAGE_SHIFT;
> -                               }
> -                               if (!ww)
> -                                       i915_gem_object_unlock(obj);
> +                       /* May arrive from get_pages on another bo */
> +                       if (!ww) {
> +                               if (!i915_gem_object_trylock(obj))
> +                                       goto skip;
> +                       } else {
> +                               err = i915_gem_object_lock(obj, ww);
> +                               if (err)
> +                                       goto skip;
>                         }
>
> +                       if (drop_pages(obj, shrink, trylock_vm) &&
> +                           !__i915_gem_object_put_pages(obj)) {
> +                               try_to_writeback(obj, shrink);
> +                               count += obj->base.size >> PAGE_SHIFT;
> +                       }
> +
> +                       if (dma_resv_test_signaled(obj->base.resv, true))
> +                               dma_resv_add_excl_fence(obj->base.resv, NULL);

I assume we want to rip out resv_prune here in the series, or
something? Instead of randomly adding this back here.

> +
> +                       if (!ww)
> +                               i915_gem_object_unlock(obj);
> +
>                         scanned += obj->base.size >> PAGE_SHIFT;
>  skip:
>                         i915_gem_object_put(obj);
> --
> 2.33.0
>