Re: [PATCH RFC net-next 2/3] net: page_pool: use alloc_pages_bulk in refill code path

[Ilias Apalodimas]

Hi Jesper, 

On Wed, Feb 24, 2021 at 07:56:46PM +0100, Jesper Dangaard Brouer wrote:
> There are cases where the page_pool need to refill with pages from the
> page allocator. Some workloads cause the page_pool to release pages
> instead of recycling these pages.
> 
> For these workload it can improve performance to bulk alloc pages from
> the page-allocator to refill the alloc cache.
> 
> For XDP-redirect workload with 100G mlx5 driver (that use page_pool)
> redirecting xdp_frame packets into a veth, that does XDP_PASS to create
> an SKB from the xdp_frame, which then cannot return the page to the
> page_pool. In this case, we saw[1] an improvement of 18.8% from using
> the alloc_pages_bulk API (3,677,958 pps -> 4,368,926 pps).
> 
> [1] https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool06_alloc_pages_bulk.org
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>

[...]

> +	/* Remaining pages store in alloc.cache */
> +	list_for_each_entry_safe(page, next, &page_list, lru) {
> +		list_del(&page->lru);
> +		if (pp_flags & PP_FLAG_DMA_MAP) {
> +			page = page_pool_dma_map(pool, page);
> +			if (!page)

As I commented on the previous patch, i'd prefer the put_page() here to be
explicitly called, instead of hiding in the page_pool_dma_map()

> +				continue;
> +		}
> +		if (likely(pool->alloc.count < PP_ALLOC_CACHE_SIZE)) {
> +			pool->alloc.cache[pool->alloc.count++] = page;
> +			pool->pages_state_hold_cnt++;
> +			trace_page_pool_state_hold(pool, page,
> +						   pool->pages_state_hold_cnt);
> +		} else {
> +			put_page(page);
> +		}
> +	}
> +out:
>  	if (pool->p.flags & PP_FLAG_DMA_MAP) {
> -		page = page_pool_dma_map(pool, page);
> -		if (!page)
> +		first_page = page_pool_dma_map(pool, first_page);
> +		if (!first_page)
>  			return NULL;
>  	}
>  
[...]

Cheers
/Ilias