linux-kernel - Re: [PATCH v16 13/20] drm/shmem-helper: Switch drm_gem_shmem

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Date:   Tue, 5 Sep 2023 09:00:42 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     David Airlie <airlied@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Emma Anholt <emma@...olt.net>, Melissa Wen <mwen@...lia.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v16 13/20] drm/shmem-helper: Switch
 drm_gem_shmem_vmap/vunmap to use pin/unpin

On Sun,  3 Sep 2023 20:07:29 +0300
Dmitry Osipenko <dmitry.osipenko@...labora.com> wrote:

> The vmapped pages shall be pinned in memory and previously get/put_pages()
> were implicitly hard-pinning/unpinning the pages. This will no longer be
> the case with addition of memory shrinker because pages_use_count > 0 won't
> determine anymore whether pages are hard-pinned (they will be soft-pinned),
> while the new pages_pin_count will do the hard-pinning. Switch the
> vmap/vunmap() to use pin/unpin() functions in a preparation of addition
> of the memory shrinker support to drm-shmem.
> 
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

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

> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 19 ++++++++++++-------
>  include/drm/drm_gem_shmem_helper.h     |  2 +-
>  2 files changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index d93ebfef20c7..899f655a65bb 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -257,6 +257,14 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
>  	return ret;
>  }
>  
> +static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
> +{
> +	dma_resv_assert_held(shmem->base.resv);
> +
> +	if (refcount_dec_and_test(&shmem->pages_pin_count))
> +		drm_gem_shmem_put_pages_locked(shmem);
> +}
> +
>  /**
>   * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
>   * @shmem: shmem GEM object
> @@ -304,10 +312,7 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
>  		return;
>  
>  	dma_resv_lock(shmem->base.resv, NULL);
> -
> -	if (refcount_dec_and_test(&shmem->pages_pin_count))
> -		drm_gem_shmem_put_pages_locked(shmem);
> -
> +	drm_gem_shmem_unpin_locked(shmem);
>  	dma_resv_unlock(shmem->base.resv);
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
> @@ -345,7 +350,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>  			return 0;
>  		}
>  
> -		ret = drm_gem_shmem_get_pages_locked(shmem);
> +		ret = drm_gem_shmem_pin_locked(shmem);
>  		if (ret)
>  			goto err_zero_use;
>  
> @@ -368,7 +373,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>  
>  err_put_pages:
>  	if (!obj->import_attach)
> -		drm_gem_shmem_put_pages_locked(shmem);
> +		drm_gem_shmem_unpin_locked(shmem);
>  err_zero_use:
>  	shmem->vmap_use_count = 0;
>  
> @@ -405,7 +410,7 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
>  			return;
>  
>  		vunmap(shmem->vaddr);
> -		drm_gem_shmem_put_pages_locked(shmem);
> +		drm_gem_shmem_unpin_locked(shmem);
>  	}
>  
>  	shmem->vaddr = NULL;
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index bd545428a7ee..396958a98c34 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -137,7 +137,7 @@ int drm_gem_shmem_madvise_locked(struct drm_gem_shmem_object *shmem, int madv);
>  static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
>  {
>  	return (shmem->madv > 0) &&
> -		!shmem->vmap_use_count && shmem->sgt &&
> +		!refcount_read(&shmem->pages_pin_count) && shmem->sgt &&
>  		!shmem->base.dma_buf && !shmem->base.import_attach;
>  }
>