[RFC v3 5/8] dmabuf: Add gpu cgroup charge transfer function

[Michal Koutný]

Hello.

On Wed, Mar 09, 2022 at 04:52:15PM +0000, "T.J. Mercier" <tjmercier at google.com> wrote:
> +int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg)
> +{
> +#ifdef CONFIG_CGROUP_GPU
> +	struct gpucg *current_gpucg;
> +	int ret = 0;
> +
> +	/*
> +	 * Verify that the cgroup of the process requesting the transfer is the
> +	 * same as the one the buffer is currently charged to.
> +	 */
> +	current_gpucg = gpucg_get(current);
> +	mutex_lock(&dmabuf->lock);
> +	if (current_gpucg != dmabuf->gpucg) {
> +		ret = -EPERM;
> +		goto err;
> +	}

Add a shortcut for gpucg == current_gpucg?

> +
> +	ret = gpucg_try_charge(gpucg, dmabuf->gpucg_dev, dmabuf->size);
> +	if (ret)
> +		goto err;
> +
> +	dmabuf->gpucg = gpucg;
> +
> +	/* uncharge the buffer from the cgroup it's currently charged to. */
> +	gpucg_uncharge(current_gpucg, dmabuf->gpucg_dev, dmabuf->size);

I think gpucg_* API would need to cater for such transfers too since
possibly transitional breach of a limit during the transfer may
unnecessarily fail the operation.

My 0.02€,
Michal