linux-kernel - Re: [PATCH net-next] page_pool: split types and declarations from page

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Date:   Mon, 24 Jul 2023 17:14:01 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexander Lobakin <aleksander.lobakin@...el.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Fang <wei.fang@....com>,
        Shenwei Wang <shenwei.wang@....com>,
        Clark Wang <xiaoning.wang@....com>,
        NXP Linux Team <linux-imx@....com>,
        Sunil Goutham <sgoutham@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        hariprasad <hkelam@...vell.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Felix Fietkau <nbd@....name>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Shayne Chen <shayne.chen@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Kalle Valo <kvalo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
        linux-wireless@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next] page_pool: split types and declarations from
 page_pool.h

On Wed, Jul 19, 2023 at 08:13:37PM +0800, Yunsheng Lin wrote:

Hi Yunsheng,

...

> diff --git a/include/net/page_pool_types.h b/include/net/page_pool_types.h

...

> +struct page_pool {
> +	struct page_pool_params p;
> +
> +	struct delayed_work release_dw;
> +	void (*disconnect)(void *);
> +	unsigned long defer_start;
> +	unsigned long defer_warn;
> +
> +	u32 pages_state_hold_cnt;
> +	unsigned int frag_offset;
> +	struct page *frag_page;
> +	long frag_users;
> +
> +#ifdef CONFIG_PAGE_POOL_STATS
> +	/* these stats are incremented while in softirq context */
> +	struct page_pool_alloc_stats alloc_stats;
> +#endif
> +	u32 xdp_mem_id;
> +
> +	/*
> +	 * Data structure for allocation side
> +	 *
> +	 * Drivers allocation side usually already perform some kind
> +	 * of resource protection.  Piggyback on this protection, and
> +	 * require driver to protect allocation side.
> +	 *
> +	 * For NIC drivers this means, allocate a page_pool per
> +	 * RX-queue. As the RX-queue is already protected by
> +	 * Softirq/BH scheduling and napi_schedule. NAPI schedule
> +	 * guarantee that a single napi_struct will only be scheduled
> +	 * on a single CPU (see napi_schedule).
> +	 */
> +	struct pp_alloc_cache alloc ____cacheline_aligned_in_smp;
> +
> +	/* Data structure for storing recycled pages.
> +	 *
> +	 * Returning/freeing pages is more complicated synchronization
> +	 * wise, because free's can happen on remote CPUs, with no
> +	 * association with allocation resource.
> +	 *
> +	 * Use ptr_ring, as it separates consumer and producer
> +	 * effeciently, it a way that doesn't bounce cache-lines.

I know this is moved from elsewhere, but: effeciently -> efficiently

> +	 *
> +	 * TODO: Implement bulk return pages into this structure.
> +	 */
> +	struct ptr_ring ring;
> +
> +#ifdef CONFIG_PAGE_POOL_STATS
> +	/* recycle stats are per-cpu to avoid locking */
> +	struct page_pool_recycle_stats __percpu *recycle_stats;
> +#endif
> +	atomic_t pages_state_release_cnt;
> +
> +	/* A page_pool is strictly tied to a single RX-queue being
> +	 * protected by NAPI, due to above pp_alloc_cache. This
> +	 * refcnt serves purpose is to simplify drivers error handling.
> +	 */
> +	refcount_t user_cnt;
> +
> +	u64 destroy_cnt;
> +};

...