netdev - Re: [net-next v1 08/16] memory-provider: dmabuf devmem memory provider

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Date: Fri, 8 Dec 2023 23:05:49 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>,
 Shailend Chand <shailend@...gle.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org,
 bpf@...r.kernel.org, linux-media@...r.kernel.org,
 dri-devel@...ts.freedesktop.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Jonathan Corbet <corbet@....net>,
 Jeroen de Borst <jeroendb@...gle.com>,
 Praveen Kaligineedi <pkaligineedi@...gle.com>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>, Arnd Bergmann
 <arnd@...db.de>, David Ahern <dsahern@...nel.org>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Shuah Khan <shuah@...nel.org>, Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 Yunsheng Lin <linyunsheng@...wei.com>,
 Harshitha Ramamurthy <hramamurthy@...gle.com>,
 Shakeel Butt <shakeelb@...gle.com>, Willem de Bruijn <willemb@...gle.com>,
 Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [net-next v1 08/16] memory-provider: dmabuf devmem memory
 provider

On 12/8/23 00:52, Mina Almasry wrote:
> Implement a memory provider that allocates dmabuf devmem page_pool_iovs.
> 
> 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 page_pool_params.
> 
> 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.
> 
> 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>
[...]
> +void __page_pool_iov_free(struct page_pool_iov *ppiov);
> +
> +static inline void page_pool_iov_put_many(struct page_pool_iov *ppiov,
> +					  unsigned int count)
> +{
> +	if (!refcount_sub_and_test(count, &ppiov->refcount))
> +		return;
> +
> +	__page_pool_iov_free(ppiov);
> +}
> +
> +/* page pool mm helpers */
> +
> +DECLARE_STATIC_KEY_FALSE(page_pool_mem_providers);
> +static inline bool page_is_page_pool_iov(const struct page *page)
> +{
> +	return static_branch_unlikely(&page_pool_mem_providers) &&
> +	       (unsigned long)page & PP_IOV;

Are there any recommendations of not using static keys in widely
used inline functions? I'm not familiar with static key code
generation, but I think the compiler will bloat users with fat chunks
of code in unlikely paths. And I'd assume it creates an array of all
uses, which it'll be walked on enabling/disabling the branch.

> +}
> +
> +static inline struct page_pool_iov *page_to_page_pool_iov(struct page *page)
> +{
> +	if (page_is_page_pool_iov(page))
> +		return (struct page_pool_iov *)((unsigned long)page & ~PP_IOV);
> +
> +	DEBUG_NET_WARN_ON_ONCE(true);
> +	return NULL;
> +}
> +
>   /**
>    * page_pool_dev_alloc_pages() - allocate a page.
>    * @pool:	pool from which to allocate
-- 
Pavel Begunkov