On Sun, 3 Sep 2023 20:07:28 +0300
Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote:
> Add lockless drm_gem_shmem_get_pages() helper that skips taking reservation
> lock if pages_use_count is non-zero, leveraging from atomicity of the
> refcount_t. Make drm_gem_shmem_mmap() to utilize the new helper.
>
> Suggested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index a0faef3e762d..d93ebfef20c7 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -227,6 +227,20 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
>
> +static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> +{
> + int ret;
> +
> + if (refcount_inc_not_zero(&shmem->pages_use_count))
> + return 0;
> +
> + dma_resv_lock(shmem->base.resv, NULL);
> + ret = drm_gem_shmem_get_pages_locked(shmem);
> + dma_resv_unlock(shmem->base.resv);
> +
> + return ret;
> +}
> +
> static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
> {
> int ret;
> @@ -610,10 +624,7 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
> return ret;
> }
>
> - dma_resv_lock(shmem->base.resv, NULL);
> - ret = drm_gem_shmem_get_pages_locked(shmem);
> - dma_resv_unlock(shmem->base.resv);
> -
> + ret = drm_gem_shmem_get_pages(shmem);
> if (ret)
> return ret;
>
