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

On Wed, 24 Feb 2021 22:15:22 +0200
Ilias Apalodimas [off-list ref] wrote:

Hi Jesper, 

On Wed, Feb 24, 2021 at 07:56:46PM +0100, Jesper Dangaard Brouer wrote:

quoted

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 <redacted>  

[...]

quoted

+	/* 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()

I fully agree.  I will fixup the code.

quoted

+				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;
 	}
   

[...]

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer