Re: [net-next v5 PATCH] page_pool: handle page recycle for NUMA_NO_NODE condition

[Ilias Apalodimas]

Hi Jesper, 

I like the overall approach since this moves the check out of  the hotpath. 
@Saeed, since i got no hardware to test this on, would it be possible to check
that it still works fine for mlx5?

[...]
> +	struct ptr_ring *r = &pool->ring;
> +	struct page *page;
> +	int pref_nid; /* preferred NUMA node */
> +
> +	/* Quicker fallback, avoid locks when ring is empty */
> +	if (__ptr_ring_empty(r))
> +		return NULL;
> +
> +	/* Softirq guarantee CPU and thus NUMA node is stable. This,
> +	 * assumes CPU refilling driver RX-ring will also run RX-NAPI.
> +	 */
> +	pref_nid = (pool->p.nid == NUMA_NO_NODE) ? numa_mem_id() : pool->p.nid;

One of the use cases for this is that during the allocation we are not
guaranteed to pick up the correct NUMA node. 
This will get automatically fixed once the driver starts recycling packets. 

I don't feel strongly about this, since i don't usually like hiding value
changes from the user but, would it make sense to move this into 
__page_pool_alloc_pages_slow() and change the pool->p.nid?

Since alloc_pages_node() will replace NUMA_NO_NODE with numa_mem_id()
regardless, why not store the actual node in our page pool information?
You can then skip this and check pool->p.nid == numa_mem_id(), regardless of
what's configured. 

Thanks
/Ilias