netdev - Re: [PATCH net-next v12 07/13] memory-provider: dmabuf devmem memory provider

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Message-ID: <14b7af66-04fe-4b49-94d6-bea5d554252e@gmail.com>
Date: Mon, 17 Jun 2024 15:45:42 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
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Subject: Re: [PATCH net-next v12 07/13] memory-provider: dmabuf devmem memory
 provider

On 6/13/24 02:35, Mina Almasry wrote:
> Implement a memory provider that allocates dmabuf devmem in the form of
> net_iov.
> 
> The provider receives a reference to the struct netdev_dmabuf_binding
> via the pool->mp_priv pointer. The driver needs to set this pointer for
> the provider in the net_iov.
> 
> The provider obtains a reference on the netdev_dmabuf_binding which
> guarantees the binding and the underlying mapping remains alive until
> the provider is destroyed.
> 
> Usage of PP_FLAG_DMA_MAP is required for this memory provide such that
> the page_pool can provide the driver with the dma-addrs of the devmem.
> 
> Support for PP_FLAG_DMA_SYNC_DEV is omitted for simplicity & p.order !=
> 0.
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz@...gle.com>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>

Comments below, apart from them

Reviewed-by: Pavel Begunkov <asml.silence@...il.com>

> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index f4fd9b9dbb675..d3843eade5fc2 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -17,6 +17,7 @@
...
> +
> +bool mp_dmabuf_devmem_release_page(struct page_pool *pool, netmem_ref netmem)
> +{
> +	WARN_ON_ONCE(!netmem_is_net_iov(netmem));
> +	WARN_ON_ONCE(atomic_long_read(netmem_get_pp_ref_count_ref(netmem)) !=
> +		     1);

If you're adding it anyway, maybe
"if (warn) return" ?

> +
> +	page_pool_clear_pp_info(netmem);
> +
> +	net_devmem_free_dmabuf(netmem_to_net_iov(netmem));
> +
> +	/* We don't want the page pool put_page()ing our net_iovs. */
> +	return false;
> +}
> +
>   #endif
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 1152e3547795a..22e3c58648d42 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -13,6 +13,7 @@
...
> @@ -269,7 +275,25 @@ static int page_pool_init(struct page_pool *pool,
>   	if (pool->dma_map)
>   		get_device(pool->p.dev);
>   
> +	if (pool->p.queue)
> +		pool->mp_priv = READ_ONCE(pool->p.queue->mp_params.mp_priv);
> +
> +	if (pool->mp_priv) {
> +		err = mp_dmabuf_devmem_init(pool);
> +		if (err) {
> +			pr_warn("%s() mem-provider init failed %d\n", __func__,
> +				err);
> +			goto free_ptr_ring;

Should also free stats, look up

free_percpu(pool->recycle_stats);

-- 
Pavel Begunkov