netdev - Re: [bpf-next V5 PATCH 11/15] page_pool: refurbish version of page

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Date:   Fri, 23 Mar 2018 06:37:30 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
        BjörnTöpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com
Cc:     eugenia@...lanox.com, Jason Wang <jasowang@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>, galp@...lanox.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [bpf-next V5 PATCH 11/15] page_pool: refurbish version of
 page_pool code



On 03/23/2018 05:18 AM, Jesper Dangaard Brouer wrote:


> +#define PP_ALLOC_CACHE_SIZE	128
> +#define PP_ALLOC_CACHE_REFILL	64
> +struct pp_alloc_cache {
> +	u32 count ____cacheline_aligned_in_smp;
> +	void *cache[PP_ALLOC_CACHE_SIZE];
> +};
> +
> +struct page_pool_params {
...
> +};
> +#define	PAGE_POOL_PARAMS_SIZE	offsetof(struct page_pool_params, end_marker)
> +
> +struct page_pool {
> +	struct page_pool_params p;
> +
> +	struct pp_alloc_cache alloc;
> +
>...
> +	struct ptr_ring ring;
> +
> +	struct rcu_head rcu;
> +};
> +


The placement of ____cacheline_aligned_in_smp in pp_alloc_cache is odd.

I would rather put it in struct page_pool as in :

+struct page_pool {
+	struct page_pool_params p;

+	struct pp_alloc_cache alloc ____cacheline_aligned_in_smp;;

To make clear the intent here (let the page_pool_params being in a read only cache line)

Also you probably can move the struct rcu_head  between p and pp_alloc_cache_alloc to fill a hole.

(assuming allowing variable sized params is no longer needed)