Re: [Intel-gfx] [PATCH 2/7] drm/i915/gem: Refactor placement setup for i915_gem_object_create*

[Matthew Auld <matthew.william.auld@gmail.com>]

On Thu, 15 Jul 2021 at 23:39, Jason Ekstrand <jason@jlekstrand.net> wrote:
>
> Since we don't allow changing the set of regions after creation, we can
> make ext_set_placements() build up the region set directly in the
> create_ext and assign it to the object later.  This is similar to what
> we did for contexts with the proto-context only simpler because there's
> no funny object shuffling.  This will be used in the next patch to allow
> us to de-duplicate a bunch of code.  Also, since we know the maximum
> number of regions up-front, we can use a fixed-size temporary array for
> the regions.  This simplifies memory management a bit for this new
> delayed approach.
>
> Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>

I think the plan was to have each extension directly hang/apply their
state on the vanilla/proto object, or at least that was the idea
behind: 357814f878f9 ("drm/i915: rework gem_create flow for upcoming
extensions"). A previous version looked similar to this IIRC.

> ---
>  drivers/gpu/drm/i915/gem/i915_gem_create.c | 75 +++++++++++++---------
>  1 file changed, 45 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> index 51f92e4b1a69d..391c8c4a12172 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> @@ -27,10 +27,13 @@ static u32 object_max_page_size(struct drm_i915_gem_object *obj)
>         return max_page_size;
>  }
>
> -static void object_set_placements(struct drm_i915_gem_object *obj,
> -                                 struct intel_memory_region **placements,
> -                                 unsigned int n_placements)
> +static int object_set_placements(struct drm_i915_gem_object *obj,
> +                                struct intel_memory_region **placements,
> +                                unsigned int n_placements)
>  {
> +       struct intel_memory_region **arr;
> +       unsigned int i;
> +
>         GEM_BUG_ON(!n_placements);
>
>         /*
> @@ -44,9 +47,20 @@ static void object_set_placements(struct drm_i915_gem_object *obj,
>                 obj->mm.placements = &i915->mm.regions[mr->id];
>                 obj->mm.n_placements = 1;
>         } else {
> -               obj->mm.placements = placements;
> +               arr = kmalloc_array(n_placements,
> +                                   sizeof(struct intel_memory_region *),
> +                                   GFP_KERNEL);
> +               if (!arr)
> +                       return -ENOMEM;
> +
> +               for (i = 0; i < n_placements; i++)
> +                       arr[i] = placements[i];
> +
> +               obj->mm.placements = arr;
>                 obj->mm.n_placements = n_placements;
>         }
> +
> +       return 0;
>  }
>
>  static int i915_gem_publish(struct drm_i915_gem_object *obj,
> @@ -148,7 +162,9 @@ i915_gem_dumb_create(struct drm_file *file,
>                 return -ENOMEM;
>
>         mr = intel_memory_region_by_type(to_i915(dev), mem_type);
> -       object_set_placements(obj, &mr, 1);
> +       ret = object_set_placements(obj, &mr, 1);
> +       if (ret)
> +               goto object_free;
>
>         ret = i915_gem_setup(obj, args->size);
>         if (ret)
> @@ -184,7 +200,9 @@ i915_gem_create_ioctl(struct drm_device *dev, void *data,
>                 return -ENOMEM;
>
>         mr = intel_memory_region_by_type(i915, INTEL_MEMORY_SYSTEM);
> -       object_set_placements(obj, &mr, 1);
> +       ret = object_set_placements(obj, &mr, 1);
> +       if (ret)
> +               goto object_free;
>
>         ret = i915_gem_setup(obj, args->size);
>         if (ret)
> @@ -197,9 +215,12 @@ i915_gem_create_ioctl(struct drm_device *dev, void *data,
>         return ret;
>  }
>
> +#define MAX_N_PLACEMENTS = (INTEL_REGION_UNKNOWN + 1)

Unused?

> +
>  struct create_ext {
>         struct drm_i915_private *i915;
> -       struct drm_i915_gem_object *vanilla_object;
> +       struct intel_memory_region *placements[INTEL_REGION_UNKNOWN];
> +       unsigned int n_placements;
>  };
>
>  static void repr_placements(char *buf, size_t size,
> @@ -230,8 +251,7 @@ static int set_placements(struct drm_i915_gem_create_ext_memory_regions *args,
>         struct drm_i915_private *i915 = ext_data->i915;
>         struct drm_i915_gem_memory_class_instance __user *uregions =
>                 u64_to_user_ptr(args->regions);
> -       struct drm_i915_gem_object *obj = ext_data->vanilla_object;
> -       struct intel_memory_region **placements;
> +       struct intel_memory_region *placements[INTEL_REGION_UNKNOWN];
>         u32 mask;
>         int i, ret = 0;
>
> @@ -245,6 +265,8 @@ static int set_placements(struct drm_i915_gem_create_ext_memory_regions *args,
>                 ret = -EINVAL;
>         }
>
> +       BUILD_BUG_ON(ARRAY_SIZE(i915->mm.regions) != ARRAY_SIZE(placements));
> +       BUILD_BUG_ON(ARRAY_SIZE(ext_data->placements) != ARRAY_SIZE(placements));
>         if (args->num_regions > ARRAY_SIZE(i915->mm.regions)) {
>                 drm_dbg(&i915->drm, "num_regions is too large\n");
>                 ret = -EINVAL;
> @@ -253,12 +275,6 @@ static int set_placements(struct drm_i915_gem_create_ext_memory_regions *args,
>         if (ret)
>                 return ret;
>
> -       placements = kmalloc_array(args->num_regions,
> -                                  sizeof(struct intel_memory_region *),
> -                                  GFP_KERNEL);
> -       if (!placements)
> -               return -ENOMEM;
> -
>         mask = 0;
>         for (i = 0; i < args->num_regions; i++) {
>                 struct drm_i915_gem_memory_class_instance region;
> @@ -293,14 +309,13 @@ static int set_placements(struct drm_i915_gem_create_ext_memory_regions *args,
>                 ++uregions;
>         }
>
> -       if (obj->mm.placements) {
> +       if (ext_data->n_placements) {
>                 ret = -EINVAL;
>                 goto out_dump;
>         }
>
> -       object_set_placements(obj, placements, args->num_regions);
> -       if (args->num_regions == 1)
> -               kfree(placements);
> +       for (i = 0; i < args->num_regions; i++)
> +               ext_data->placements[i] = placements[i];

kfree(placements) is still in the error unwind?