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

Matthew Auld
2021-10-21T16:13:20Z

On Thu, 21 Oct 2021 at 11:37, Maarten Lankhorst
<maarten.lankhorst@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@linux.intel.com>
> Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@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
>