Re: [PATCH 5/5] net: page_pool: use alloc_pages_bulk in refill code path

[Ilias Apalodimas]

On Mon, Mar 01, 2021 at 04:12:00PM +0000, Mel Gorman wrote:
> From: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> 
> 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>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> ---
>  net/core/page_pool.c | 63 ++++++++++++++++++++++++++++----------------
>  1 file changed, 40 insertions(+), 23 deletions(-)
> 
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index a26f2ceb6a87..567680bd91c4 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -208,44 +208,61 @@ noinline
>  static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>  						 gfp_t _gfp)
>  {
> +	const int bulk = PP_ALLOC_CACHE_REFILL;
> +	struct page *page, *next, *first_page;
>  	unsigned int pp_flags = pool->p.flags;
> -	struct page *page;
> +	unsigned int pp_order = pool->p.order;
> +	int pp_nid = pool->p.nid;
> +	LIST_HEAD(page_list);
>  	gfp_t gfp = _gfp;
>  
> -	/* We could always set __GFP_COMP, and avoid this branch, as
> -	 * prep_new_page() can handle order-0 with __GFP_COMP.
> -	 */
> -	if (pool->p.order)
> +	/* Don't support bulk alloc for high-order pages */
> +	if (unlikely(pp_order)) {
>  		gfp |= __GFP_COMP;
> +		first_page = alloc_pages_node(pp_nid, gfp, pp_order);
> +		if (unlikely(!first_page))
> +			return NULL;
> +		goto out;
> +	}
>  
> -	/* FUTURE development:
> -	 *
> -	 * Current slow-path essentially falls back to single page
> -	 * allocations, which doesn't improve performance.  This code
> -	 * need bulk allocation support from the page allocator code.
> -	 */
> -
> -	/* Cache was empty, do real allocation */
> -#ifdef CONFIG_NUMA
> -	page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
> -#else
> -	page = alloc_pages(gfp, pool->p.order);
> -#endif
> -	if (!page)
> +	if (unlikely(!__alloc_pages_bulk_nodemask(gfp, pp_nid, NULL,
> +						  bulk, &page_list)))
>  		return NULL;
>  
> +	/* First page is extracted and returned to caller */
> +	first_page = list_first_entry(&page_list, struct page, lru);
> +	list_del(&first_page->lru);
> +
> +	/* 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 &&
> +		    unlikely(!page_pool_dma_map(pool, page))) {
> +			put_page(page);
> +			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 (pp_flags & PP_FLAG_DMA_MAP &&
> -	    unlikely(!page_pool_dma_map(pool, page))) {
> -		put_page(page);
> +	    unlikely(!page_pool_dma_map(pool, first_page))) {
> +		put_page(first_page);
>  		return NULL;
>  	}
>  
>  	/* Track how many pages are held 'in-flight' */
>  	pool->pages_state_hold_cnt++;
> -	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);
> +	trace_page_pool_state_hold(pool, first_page, pool->pages_state_hold_cnt);
>  
>  	/* When page just alloc'ed is should/must have refcnt 1. */
> -	return page;
> +	return first_page;
>  }
>  
>  /* For using page_pool replace: alloc_pages() API calls, but provide
> -- 
> 2.26.2
> 

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>