linux-kernel - Re: [RFC 4/6] dma-buf: Add DMA-BUF exporter op to charge a DMA-BUF to a cgroup.

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Date:   Mon, 17 Jan 2022 08:46:16 +0100
From:   Christian König <christian.koenig@....com>
To:     Hridya Valsaraju <hridya@...gle.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <john.stultz@...aro.org>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dave Airlie <airlied@...hat.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Matthew Auld <matthew.auld@...el.com>,
        Matthew Brost <matthew.brost@...el.com>,
        Li Li <dualli@...gle.com>, Marco Ballesio <balejs@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Hang Lu <hangl@...eaurora.org>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Chris Down <chris@...isdown.name>,
        Vipin Sharma <vipinsh@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Arnd Bergmann <arnd@...db.de>, dri-devel@...ts.freedesktop.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
        cgroups@...r.kernel.org
Cc:     Kenny.Ho@....com, daniels@...labora.com, kaleshsingh@...gle.com,
        tjmercier@...gle.com
Subject: Re: [RFC 4/6] dma-buf: Add DMA-BUF exporter op to charge a DMA-BUF to
 a cgroup.

Am 15.01.22 um 02:06 schrieb Hridya Valsaraju:
> The optional exporter op provides a way for processes to transfer
> charge of a buffer to a different process. This is essential for the
> cases where a central allocator process does allocations for various
> subsystems, hands over the fd to the client who
> requested the memory and drops all references to the allocated memory.
>
> Signed-off-by: Hridya Valsaraju <hridya@...gle.com>
> ---
>   include/linux/dma-buf.h | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 7ab50076e7a6..d5e52f81cc6f 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -13,6 +13,7 @@
>   #ifndef __DMA_BUF_H__
>   #define __DMA_BUF_H__
>   
> +#include <linux/cgroup_gpu.h>
>   #include <linux/dma-buf-map.h>
>   #include <linux/file.h>
>   #include <linux/err.h>
> @@ -285,6 +286,23 @@ struct dma_buf_ops {
>   
>   	int (*vmap)(struct dma_buf *dmabuf, struct dma_buf_map *map);
>   	void (*vunmap)(struct dma_buf *dmabuf, struct dma_buf_map *map);
> +
> +	/**
> +	 * @charge_to_cgroup:
> +	 *
> +	 * This is called by an exporter to charge a buffer to the specified
> +	 * cgroup.

Well that sentence makes absolutely no sense at all.

The dma_buf_ops are supposed to be called by the DMA-buf subsystem on 
behalves of the importer and never by the exporter itself.

I hope that this is just a documentation mixup.

Regards,
Christian.

>   The caller must hold a reference to @gpucg obtained via
> +	 * gpucg_get(). The DMA-BUF will be uncharged from the cgroup it is
> +	 * currently charged to before being charged to @gpucg. The caller must
> +	 * belong to the cgroup the buffer is currently charged to.
> +	 *
> +	 * This callback is optional.
> +	 *
> +	 * Returns:
> +	 *
> +	 * 0 on success or negative error code on failure.
> +	 */
> +	int (*charge_to_cgroup)(struct dma_buf *dmabuf, struct gpucg *gpucg);
>   };
>   
>   /**