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

Jesper Dangaard Brouer
2021-02-24T18:59:37Z

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>
---
net/core/page_pool.c | 65 ++++++++++++++++++++++++++++++++------------------
1 file changed, 41 insertions(+), 24 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 50d52aa6fbeb..e0ae95fc59f0 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -210,44 +210,61 @@ noinline
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
gfp_t _gfp)
{
- struct page *page;
+ const int bulk = PP_ALLOC_CACHE_REFILL;
+ struct page *page, *next, *first_page;
+ unsigned int pp_flags = pool->p.flags;
+ 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) {
+ page = page_pool_dma_map(pool, page);
+ if (!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 (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;
}

/* 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