Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Mon, 21 Mar 2022 18:45:30 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     "T.J. Mercier" <tjmercier@google.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christian Brauner <brauner@kernel.org>,
        Hridya Valsaraju <hridya@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@redhat.com>,
        Brian Starkey <Brian.Starkey@arm.com>,
        John Stultz <john.stultz@linaro.org>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shuah Khan <shuah@kernel.org>, kaleshsingh@google.com,
        Kenny.Ho@amd.com, dri-devel@lists.freedesktop.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
        cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [RFC v3 5/8] dmabuf: Add gpu cgroup charge transfer function
Message-ID: <20220321174530.GB9640@blackbody.suse.cz>
References: <20220309165222.2843651-1-tjmercier@google.com>
 <20220309165222.2843651-6-tjmercier@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20220309165222.2843651-6-tjmercier@google.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

Hello.

On Wed, Mar 09, 2022 at 04:52:15PM +0000, "T.J. Mercier" <tjmercier@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