[PATCH net-next v2 2/3] page_pool: support non-frag page for page_pool_alloc_frag()

[Yunsheng Lin]

There is performance penalty with using page frag support when
user requests a larger frag size and a page only supports one
frag user, see [1].

It seems like user may request different frag size depending
on the mtu and packet size, provide an option to allocate
non-frag page when a whole page is not able to hold two frags,
so that user has a unified interface for the memory allocation
with least memory utilization and performance penalty.

1. https://lore.kernel.org/netdev/ZEU+vospFdm08IeE@localhost.localdomain/

Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
CC: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
CC: Alexander Duyck <alexander.duyck@xxxxxxxxx>
---
 net/core/page_pool.c | 47 +++++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 0868aa8f6323..e84ec6eabefd 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -699,14 +699,27 @@ struct page *page_pool_alloc_frag(struct page_pool *pool,
 	unsigned int max_size = PAGE_SIZE << pool->p.order;
 	struct page *page = pool->frag_page;
 
-	if (WARN_ON(!(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
-		    size > max_size))
+	if (unlikely(size > max_size))
 		return NULL;
 
+	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) {
+		*offset = 0;
+		return page_pool_alloc_pages(pool, gfp);
+	}
+
 	size = ALIGN(size, dma_get_cache_alignment());
-	*offset = pool->frag_offset;
 
-	if (page && *offset + size > max_size) {
+	if (page) {
+		*offset = pool->frag_offset;
+
+		if (*offset + size <= max_size) {
+			pool->frag_users++;
+			pool->frag_offset = *offset + size;
+			alloc_stat_inc(pool, fast);
+			return page;
+		}
+
+		pool->frag_page = NULL;
 		page = page_pool_drain_frag(pool, page);
 		if (page) {
 			alloc_stat_inc(pool, fast);
@@ -714,26 +727,24 @@ struct page *page_pool_alloc_frag(struct page_pool *pool,
 		}
 	}
 
-	if (!page) {
-		page = page_pool_alloc_pages(pool, gfp);
-		if (unlikely(!page)) {
-			pool->frag_page = NULL;
-			return NULL;
-		}
-
-		pool->frag_page = page;
+	page = page_pool_alloc_pages(pool, gfp);
+	if (unlikely(!page))
+		return NULL;
 
 frag_reset:
-		pool->frag_users = 1;
+	/* return page as non-frag page if a page is not able to
+	 * hold two frags for the current requested size.
+	 */
+	if (unlikely(size << 1 > max_size)) {
 		*offset = 0;
-		pool->frag_offset = size;
-		page_pool_fragment_page(page, BIAS_MAX);
 		return page;
 	}
 
-	pool->frag_users++;
-	pool->frag_offset = *offset + size;
-	alloc_stat_inc(pool, fast);
+	pool->frag_page = page;
+	pool->frag_users = 1;
+	*offset = 0;
+	pool->frag_offset = size;
+	page_pool_fragment_page(page, BIAS_MAX);
 	return page;
 }
 EXPORT_SYMBOL(page_pool_alloc_frag);
-- 
2.33.0