mlx4: allow order-0 memory allocations in RX path

Signed-off-by: Eric Dumazet <edumazet@google.com>

mlx4 exclusively uses order-2 allocations in RX path, which are
likely to fail under memory pressure.

We therefore drop frames more than needed.

This patch tries order-3, order-2, order-1 and finally order-0
allocations to keep good performance, yet allow allocations if/when
memory gets fragmented.

By using larger pages, and avoiding unnecessary get_page()/put_page()
on compound pages, this patch improves performance as well, lowering
false sharing on struct page.

Also use GFP_KERNEL allocations in initialization path, as allocating 12
MB (390 order-3 pages) can easily fail with GFP_ATOMIC.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Amir Vadai <amirv@mellanox.com>
Acked-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -43,41 +43,65 @@
 
 #include "mlx4_en.h"
 
+static int mlx4_alloc_pages(struct mlx4_en_priv *priv,
+			    struct mlx4_en_rx_alloc *page_alloc,
+			    const struct mlx4_en_frag_info *frag_info,
+			    gfp_t _gfp)
+{
+	int order;
+	struct page *page;
+	dma_addr_t dma;
+
+	for (order = MLX4_EN_ALLOC_PREFER_ORDER; ;) {
+		gfp_t gfp = _gfp;
+
+		if (order)
+			gfp |= __GFP_COMP | __GFP_NOWARN;
+		page = alloc_pages(gfp, order);
+		if (likely(page))
+			break;
+		if (--order < 0 ||
+		    ((PAGE_SIZE << order) < frag_info->frag_size))
+			return -ENOMEM;
+	}
+	dma = dma_map_page(priv->ddev, page, 0, PAGE_SIZE << order,
+			   PCI_DMA_FROMDEVICE);
+	if (dma_mapping_error(priv->ddev, dma)) {
+		put_page(page);
+		return -ENOMEM;
+	}
+	page_alloc->size = PAGE_SIZE << order;
+	page_alloc->page = page;
+	page_alloc->dma = dma;
+	page_alloc->offset = frag_info->frag_align;
+	/* Not doing get_page() for each frag is a big win
+	 * on asymetric workloads.
+	 */
+	atomic_set(&page->_count, page_alloc->size / frag_info->frag_stride);
+	return 0;
+}
+
 static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv,
 			       struct mlx4_en_rx_desc *rx_desc,
 			       struct mlx4_en_rx_alloc *frags,
-			       struct mlx4_en_rx_alloc *ring_alloc)
+			       struct mlx4_en_rx_alloc *ring_alloc,
+			       gfp_t gfp)
 {
 	struct mlx4_en_rx_alloc page_alloc[MLX4_EN_MAX_RX_FRAGS];
-	struct mlx4_en_frag_info *frag_info;
+	const struct mlx4_en_frag_info *frag_info;
 	struct page *page;
 	dma_addr_t dma;
 	int i;
 
 	for (i = 0; i < priv->num_frags; i++) {
 		frag_info = &priv->frag_info[i];
-		if (ring_alloc[i].offset == frag_info->last_offset) {
-			page = alloc_pages(GFP_ATOMIC | __GFP_COMP,
-					MLX4_EN_ALLOC_ORDER);
-			if (!page)
-				goto out;
-			dma = dma_map_page(priv->ddev, page, 0,
-				MLX4_EN_ALLOC_SIZE, PCI_DMA_FROMDEVICE);
-			if (dma_mapping_error(priv->ddev, dma)) {
-				put_page(page);
+		page_alloc[i] = ring_alloc[i];
+		page_alloc[i].offset += frag_info->frag_stride;
+		if (page_alloc[i].offset + frag_info->frag_stride <= ring_alloc[i].size)
+			continue;
+		if (mlx4_alloc_pages(priv, &page_alloc[i], frag_info, gfp))
 			goto out;
 	}
-			page_alloc[i].page = page;
-			page_alloc[i].dma = dma;
-			page_alloc[i].offset = frag_info->frag_align;
-		} else {
-			page_alloc[i].page = ring_alloc[i].page;
-			get_page(ring_alloc[i].page);
-			page_alloc[i].dma = ring_alloc[i].dma;
-			page_alloc[i].offset = ring_alloc[i].offset +
-						frag_info->frag_stride;
-		}
-	}
 
 	for (i = 0; i < priv->num_frags; i++) {
 		frags[i] = ring_alloc[i];
@@ -88,14 +112,16 @@ static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv,
 
 	return 0;
 
-
 out:
 	while (i--) {
 		frag_info = &priv->frag_info[i];
-		if (ring_alloc[i].offset == frag_info->last_offset)
+		if (page_alloc[i].page != ring_alloc[i].page) {
 			dma_unmap_page(priv->ddev, page_alloc[i].dma,
-				MLX4_EN_ALLOC_SIZE, PCI_DMA_FROMDEVICE);
-		put_page(page_alloc[i].page);
+				page_alloc[i].size, PCI_DMA_FROMDEVICE);
+			page = page_alloc[i].page;
+			atomic_set(&page->_count, 1);
+			put_page(page);
+		}
 	}
 	return -ENOMEM;
 }
@@ -104,12 +130,12 @@ static void mlx4_en_free_frag(struct mlx4_en_priv *priv,
 			      struct mlx4_en_rx_alloc *frags,
 			      int i)
 {
-	struct mlx4_en_frag_info *frag_info = &priv->frag_info[i];
+	const struct mlx4_en_frag_info *frag_info = &priv->frag_info[i];
 
-	if (frags[i].offset == frag_info->last_offset) {
-		dma_unmap_page(priv->ddev, frags[i].dma, MLX4_EN_ALLOC_SIZE,
+	if (frags[i].offset + frag_info->frag_stride > frags[i].size)
+		dma_unmap_page(priv->ddev, frags[i].dma, frags[i].size,
 					 PCI_DMA_FROMDEVICE);
-	}
+
 	if (frags[i].page)
 		put_page(frags[i].page);
 }
@@ -117,35 +143,28 @@ static void mlx4_en_free_frag(struct mlx4_en_priv *priv,
 static int mlx4_en_init_allocator(struct mlx4_en_priv *priv,
 				  struct mlx4_en_rx_ring *ring)
 {
-	struct mlx4_en_rx_alloc *page_alloc;
 	int i;
+	struct mlx4_en_rx_alloc *page_alloc;
 
 	for (i = 0; i < priv->num_frags; i++) {
-		page_alloc = &ring->page_alloc[i];
-		page_alloc->page = alloc_pages(GFP_ATOMIC | __GFP_COMP,
-					       MLX4_EN_ALLOC_ORDER);
-		if (!page_alloc->page)
-			goto out;
+		const struct mlx4_en_frag_info *frag_info = &priv->frag_info[i];
 
-		page_alloc->dma = dma_map_page(priv->ddev, page_alloc->page, 0,
-					MLX4_EN_ALLOC_SIZE, PCI_DMA_FROMDEVICE);
-		if (dma_mapping_error(priv->ddev, page_alloc->dma)) {
-			put_page(page_alloc->page);
-			page_alloc->page = NULL;
+		if (mlx4_alloc_pages(priv, &ring->page_alloc[i],
+				     frag_info, GFP_KERNEL))
 			goto out;
 	}
-		page_alloc->offset = priv->frag_info[i].frag_align;
-		en_dbg(DRV, priv, "Initialized allocator:%d with page:%p\n",
-		       i, page_alloc->page);
-	}
 	return 0;
 
 out:
 	while (i--) {
+		struct page *page;
+
 		page_alloc = &ring->page_alloc[i];
 		dma_unmap_page(priv->ddev, page_alloc->dma,
-				MLX4_EN_ALLOC_SIZE, PCI_DMA_FROMDEVICE);
-		put_page(page_alloc->page);
+			       page_alloc->size, PCI_DMA_FROMDEVICE);
+		page = page_alloc->page;
+		atomic_set(&page->_count, 1);
+		put_page(page);
 		page_alloc->page = NULL;
 	}
 	return -ENOMEM;
@@ -158,13 +177,18 @@ static void mlx4_en_destroy_allocator(struct mlx4_en_priv *priv,
 	int i;
 
 	for (i = 0; i < priv->num_frags; i++) {
+		const struct mlx4_en_frag_info *frag_info = &priv->frag_info[i];
+
 		page_alloc = &ring->page_alloc[i];
 		en_dbg(DRV, priv, "Freeing allocator:%d count:%d\n",
 		       i, page_count(page_alloc->page));
 
 		dma_unmap_page(priv->ddev, page_alloc->dma,
-				MLX4_EN_ALLOC_SIZE, PCI_DMA_FROMDEVICE);
+				page_alloc->size, PCI_DMA_FROMDEVICE);
+		while (page_alloc->offset + frag_info->frag_stride < page_alloc->size) {
 			put_page(page_alloc->page);
+			page_alloc->offset += frag_info->frag_stride;
+		}
 		page_alloc->page = NULL;
 	}
 }
@@ -195,13 +219,14 @@ static void mlx4_en_init_rx_desc(struct mlx4_en_priv *priv,
 }
 
 static int mlx4_en_prepare_rx_desc(struct mlx4_en_priv *priv,
-				   struct mlx4_en_rx_ring *ring, int index)
+				   struct mlx4_en_rx_ring *ring, int index,
+				   gfp_t gfp)
 {
 	struct mlx4_en_rx_desc *rx_desc = ring->buf + (index * ring->stride);
 	struct mlx4_en_rx_alloc *frags = ring->rx_info +
 					(index << priv->log_rx_info);
 
-	return mlx4_en_alloc_frags(priv, rx_desc, frags, ring->page_alloc);
+	return mlx4_en_alloc_frags(priv, rx_desc, frags, ring->page_alloc, gfp);
 }
 
 static inline void mlx4_en_update_rx_prod_db(struct mlx4_en_rx_ring *ring)
@@ -235,7 +260,8 @@ static int mlx4_en_fill_rx_buffers(struct mlx4_en_priv *priv)
 			ring = &priv->rx_ring[ring_ind];
 
 			if (mlx4_en_prepare_rx_desc(priv, ring,
-						    ring->actual_size)) {
+						    ring->actual_size,
+						    GFP_KERNEL)) {
 				if (ring->actual_size < MLX4_EN_MIN_RX_SIZE) {
 					en_err(priv, "Failed to allocate "
 						     "enough rx buffers\n");
@@ -450,11 +476,11 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv,
 					DMA_FROM_DEVICE);
 
 		/* Save page reference in skb */
-		get_page(frags[nr].page);
 		__skb_frag_set_page(&skb_frags_rx[nr], frags[nr].page);
 		skb_frag_size_set(&skb_frags_rx[nr], frag_info->frag_size);
 		skb_frags_rx[nr].page_offset = frags[nr].offset;
 		skb->truesize += frag_info->frag_stride;
+		frags[nr].page = NULL;
 	}
 	/* Adjust size of last fragment to match actual length */
 	if (nr > 0)
@@ -547,7 +573,7 @@ static void mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
 	int index = ring->prod & ring->size_mask;
 
 	while ((u32) (ring->prod - ring->cons) < ring->actual_size) {
-		if (mlx4_en_prepare_rx_desc(priv, ring, index))
+		if (mlx4_en_prepare_rx_desc(priv, ring, index, GFP_ATOMIC))
 			break;
 		ring->prod++;
 		index = ring->prod & ring->size_mask;
@@ -805,21 +831,7 @@ int mlx4_en_poll_rx_cq(struct napi_struct *napi, int budget)
 	return done;
 }
 
-
-/* Calculate the last offset position that accommodates a full fragment
- * (assuming fagment size = stride-align) */
-static int mlx4_en_last_alloc_offset(struct mlx4_en_priv *priv, u16 stride, u16 align)
-{
-	u16 res = MLX4_EN_ALLOC_SIZE % stride;
-	u16 offset = MLX4_EN_ALLOC_SIZE - stride - res + align;
-
-	en_dbg(DRV, priv, "Calculated last offset for stride:%d align:%d "
-			    "res:%d offset:%d\n", stride, align, res, offset);
-	return offset;
-}
-
-
-static int frag_sizes[] = {
+static const int frag_sizes[] = {
 	FRAG_SZ0,
 	FRAG_SZ1,
 	FRAG_SZ2,
@@ -847,9 +859,6 @@ void mlx4_en_calc_rx_buf(struct net_device *dev)
 			priv->frag_info[i].frag_stride =
 				ALIGN(frag_sizes[i], SMP_CACHE_BYTES);
 		}
-		priv->frag_info[i].last_offset = mlx4_en_last_alloc_offset(
-						priv, priv->frag_info[i].frag_stride,
-						priv->frag_info[i].frag_align);
 		buf_size += priv->frag_info[i].frag_size;
 		i++;
 	}
@@ -861,13 +870,13 @@ void mlx4_en_calc_rx_buf(struct net_device *dev)
 	en_dbg(DRV, priv, "Rx buffer scatter-list (effective-mtu:%d "
 		  "num_frags:%d):\n", eff_mtu, priv->num_frags);
 	for (i = 0; i < priv->num_frags; i++) {
-		en_dbg(DRV, priv, "  frag:%d - size:%d prefix:%d align:%d "
-				"stride:%d last_offset:%d\n", i,
+		en_err(priv,
+		       "  frag:%d - size:%d prefix:%d align:%d stride:%d\n",
+		       i,
 		       priv->frag_info[i].frag_size,
 		       priv->frag_info[i].frag_prefix_size,
 		       priv->frag_info[i].frag_align,
-				priv->frag_info[i].frag_stride,
-				priv->frag_info[i].last_offset);
+		       priv->frag_info[i].frag_stride);
 	}
 }
 

drivers/net/ethernet/mellanox/mlx4/mlx4_en.h

@@ -96,7 +96,8 @@
 
 /* Use the maximum between 16384 and a single page */
 #define MLX4_EN_ALLOC_SIZE	PAGE_ALIGN(16384)
-#define MLX4_EN_ALLOC_ORDER	get_order(MLX4_EN_ALLOC_SIZE)
+
+#define MLX4_EN_ALLOC_PREFER_ORDER	PAGE_ALLOC_COSTLY_ORDER
 
 /* Receive fragment sizes; we use at most 3 fragments (for 9600 byte MTU
  * and 4K allocations) */
@@ -236,7 +237,8 @@ struct mlx4_en_tx_desc {
 struct mlx4_en_rx_alloc {
 	struct page	*page;
 	dma_addr_t	dma;
-	u16 offset;
+	u32		offset;
+	u32		size;
 };
 
 struct mlx4_en_tx_ring {
@@ -439,8 +441,6 @@ struct mlx4_en_frag_info {
 	u16 frag_prefix_size;
 	u16 frag_stride;
 	u16 frag_align;
-	u16 last_offset;
-
 };
 
 #ifdef CONFIG_MLX4_EN_DCB