Re: [PATCH v16 10/20] drm/shmem-helper: Add and use pages_pin_count

[Boris Brezillon <boris.brezillon@collabora.com>]

On Sun,  3 Sep 2023 20:07:26 +0300
Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:

> Add separate pages_pin_count for tracking of whether drm-shmem pages are
> moveable or not. With the addition of memory shrinker support to drm-shmem,
> the pages_use_count will no longer determine whether pages are hard-pinned
> in memory, but whether pages exist and are soft-pinned (and could be swapped
> out). The pages_pin_count > 1 will hard-pin pages in memory.
> 
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 24 ++++++++++++++++--------
>  include/drm/drm_gem_shmem_helper.h     | 10 ++++++++++
>  2 files changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 25e99468ced2..7e1e674e2c9f 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -236,18 +236,16 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
>  
>  	dma_resv_assert_held(shmem->base.resv);
>  
> +	if (refcount_inc_not_zero(&shmem->pages_pin_count))
> +		return 0;
> +
>  	ret = drm_gem_shmem_get_pages_locked(shmem);
> +	if (!ret)
> +		refcount_set(&shmem->pages_pin_count, 1);
>  
>  	return ret;
>  }
>  
> -static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
> -{
> -	dma_resv_assert_held(shmem->base.resv);
> -
> -	drm_gem_shmem_put_pages_locked(shmem);
> -}
> -
>  /**
>   * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
>   * @shmem: shmem GEM object
> @@ -265,6 +263,9 @@ int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
>  
>  	drm_WARN_ON(obj->dev, obj->import_attach);
>  
> +	if (refcount_inc_not_zero(&shmem->pages_pin_count))
> +		return 0;
> +
>  	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
>  	if (ret)
>  		return ret;
> @@ -288,8 +289,14 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
>  
>  	drm_WARN_ON(obj->dev, obj->import_attach);
>  
> +	if (refcount_dec_not_one(&shmem->pages_pin_count))
> +		return;
> +
>  	dma_resv_lock(shmem->base.resv, NULL);
> -	drm_gem_shmem_unpin_locked(shmem);
> +
> +	if (refcount_dec_and_test(&shmem->pages_pin_count))
> +		drm_gem_shmem_put_pages_locked(shmem);
> +
>  	dma_resv_unlock(shmem->base.resv);
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
> @@ -634,6 +641,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
>  	if (shmem->base.import_attach)
>  		return;
>  
> +	drm_printf_indent(p, indent, "pages_pin_count=%u\n", refcount_read(&shmem->pages_pin_count));
>  	drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
>  	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
>  	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 808083279fd5..1cd74ae5761a 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -39,6 +39,16 @@ struct drm_gem_shmem_object {
>  	 */
>  	unsigned int pages_use_count;
>  
> +	/**
> +	 * @pages_pin_count:
> +	 *
> +	 * Reference count on the pinned pages table.
> +	 * The pages allowed to be evicted and purged by memory
> +	 * shrinker only when the count is zero, otherwise pages
> +	 * are hard-pinned in memory.
> +	 */
> +	refcount_t pages_pin_count;
> +
>  	/**
>  	 * @madv: State for madvise
>  	 *