netdev - Re: [PATCH RFC net-next v4 5/9] libie: add Rx buffer management (via Page Pool)

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Date: Thu, 6 Jul 2023 20:47:28 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
CC: Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Michal Kubiak
	<michal.kubiak@...el.com>, Larysa Zaremba <larysa.zaremba@...el.com>,
	Alexander Duyck <alexanderduyck@...com>, David Christensen
	<drc@...ux.vnet.ibm.com>, Jesper Dangaard Brouer <hawk@...nel.org>, Ilias
 Apalodimas <ilias.apalodimas@...aro.org>, Paul Menzel
	<pmenzel@...gen.mpg.de>, <netdev@...r.kernel.org>,
	<intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next v4 5/9] libie: add Rx buffer management (via
 Page Pool)

On 2023/7/5 23:55, Alexander Lobakin wrote:

> +/**
> + * libie_rx_page_pool_create - create a PP with the default libie settings
> + * @napi: &napi_struct covering this PP (no usage outside its poll loops)
> + * @size: size of the PP, usually simply Rx queue len
> + *
> + * Returns &page_pool on success, casted -errno on failure.
> + */
> +struct page_pool *libie_rx_page_pool_create(struct napi_struct *napi,
> +					    u32 size)
> +{
> +	struct page_pool_params pp = {
> +		.flags		= PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
> +		.order		= LIBIE_RX_PAGE_ORDER,
> +		.pool_size	= size,
> +		.nid		= NUMA_NO_NODE,
> +		.dev		= napi->dev->dev.parent,
> +		.napi		= napi,
> +		.dma_dir	= DMA_FROM_DEVICE,
> +		.offset		= LIBIE_SKB_HEADROOM,

I think it worth mentioning that the '.offset' is not really accurate
when the page is split, as we do not really know what is the offset of
the frag of a page except for the first frag.

> +	};
> +	size_t truesize;
> +
> +	pp.max_len = libie_rx_sync_len(napi->dev, pp.offset);
> +
> +	/* "Wanted" truesize, passed to page_pool_dev_alloc() */
> +	truesize = roundup_pow_of_two(SKB_HEAD_ALIGN(pp.offset + pp.max_len));
> +	pp.init_arg = (void *)truesize;

I am not sure if it is correct to use pp.init_arg here, as it is supposed to
be used along with init_callback. And if we want to change the implemetation
of init_callback, we may stuck with it as the driver is using it very
differently here.

Is it possible to pass the 'wanted true size' by adding a parameter for
libie_rx_alloc()?

> +
> +	return page_pool_create(&pp);
> +}
> +EXPORT_SYMBOL_NS_GPL(libie_rx_page_pool_create, LIBIE);