[PATCH mel-git] Followup: Update [PATCH 7/7] in Mel's series

[PATCH mel-git] Followup: Update [PATCH 7/7] in Mel's series

[Jesper Dangaard Brouer]

This patch is against Mel's git-tree:
 git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git

Using branch: mm-bulk-rebase-v4r2 but replacing the last patch related to
the page_pool using __alloc_pages_bulk().

 https://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git/log/?h=mm-bulk-rebase-v4r2

While implementing suggestions by Alexander Duyck, I realised that I could
simplify the code further, and simply take the last page from the
pool->alloc.cache given this avoids special casing the last page.

I re-ran performance tests and the improvement have been reduced to 13% from
18% before, but I don't think the rewrite of the specific patch have
anything to do with this.

Notes on tests:
 https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool06_alloc_pages_bulk.org#test-on-mel-git-tree

---

Jesper Dangaard Brouer (1):
      net: page_pool: use alloc_pages_bulk in refill code path


 net/core/page_pool.c |   73 ++++++++++++++++++++++++++++++++------------------
 1 file changed, 47 insertions(+), 26 deletions(-)

--

[PATCH mel-git] net: page_pool: use alloc_pages_bulk in refill code path

[Jesper Dangaard Brouer]

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 13% from using
the alloc_pages_bulk API (3,810,013 pps -> 4,308,208 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>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 net/core/page_pool.c |   73 ++++++++++++++++++++++++++++++++------------------
 1 file changed, 47 insertions(+), 26 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 40e1b2beaa6c..7c194335c066 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -203,38 +203,17 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 	return true;
 }
 
-/* slow path */
-noinline
-static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
-						 gfp_t _gfp)
+static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
+						 gfp_t gfp)
 {
-	unsigned int pp_flags = pool->p.flags;
 	struct page *page;
-	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)
-		gfp |= __GFP_COMP;
-
-	/* 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
+	gfp |= __GFP_COMP;
 	page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
-#else
-	page = alloc_pages(gfp, pool->p.order);
-#endif
-	if (!page)
+	if (unlikely(!page))
 		return NULL;
 
-	if ((pp_flags & PP_FLAG_DMA_MAP) &&
+	if ((pool->p.flags & PP_FLAG_DMA_MAP) &&
 	    unlikely(!page_pool_dma_map(pool, page))) {
 		put_page(page);
 		return NULL;
@@ -243,6 +222,48 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	/* 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);
+	return page;
+}
+
+/* slow path */
+noinline
+static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
+						 gfp_t gfp)
+{
+	const int bulk = PP_ALLOC_CACHE_REFILL;
+	unsigned int pp_flags = pool->p.flags;
+	unsigned int pp_order = pool->p.order;
+	int pp_nid = pool->p.nid;
+	struct page *page, *next;
+	LIST_HEAD(page_list);
+
+	/* Don't support bulk alloc for high-order pages */
+	if (unlikely(pp_order))
+		return __page_pool_alloc_page_order(pool, gfp);
+
+	if (unlikely(!__alloc_pages_bulk(gfp, pp_nid, NULL, bulk, &page_list)))
+		return NULL;
+
+	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;
+		}
+		/* Alloc cache have room as it is empty on function call */
+		pool->alloc.cache[pool->alloc.count++] = page;
+		/* 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);
+	}
+
+	/* Return last page */
+	if (likely(pool->alloc.count > 0))
+		page = pool->alloc.cache[--pool->alloc.count];
+	else
+		page = NULL;
 
 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;