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

Ilias Apalodimas
2021-02-24T20:18:30Z

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@redhat.com>

[...]

> + /* 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