netdev - [net-next] stmmac: limit max_mtu in case of 4KiB and use __netdev_alloc

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Message-Id: <1318937995-14228-1-git-send-email-peppe.cavallaro@st.com>
Date:	Tue, 18 Oct 2011 13:39:55 +0200
From:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, eric.dumazet@...il.com,
	Giuseppe Cavallaro <peppe.cavallaro@...com>
Subject: [net-next] stmmac: limit max_mtu in case of 4KiB and use __netdev_alloc_skb (V2)

Problem using big mtu around 4096 bytes is you end allocating (4096
+NET_SKB_PAD + NET_IP_ALIGN + sizeof(struct skb_shared_info) bytes ->
8192 bytes : order-1 pages

It's better to limit the mtu to SKB_MAX_HEAD(NET_SKB_PAD),
to have no more than one page per skb.

Also the patch changes the netdev_alloc_skb_ip_align() done in
init_dma_desc_rings() and uses a variant allowing GFP_KERNEL allocations
allowing the driver to load even in case of memory pressure.

Reported-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@...com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 1848a16..6b8f455 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -474,11 +474,13 @@ static void init_dma_desc_rings(struct net_device *dev)
 	for (i = 0; i < rxsize; i++) {
 		struct dma_desc *p = priv->dma_rx + i;
 
-		skb = netdev_alloc_skb_ip_align(dev, bfsize);
+		skb = __netdev_alloc_skb(dev, bfsize + NET_IP_ALIGN,
+					 GFP_KERNEL);
 		if (unlikely(skb == NULL)) {
 			pr_err("%s: Rx init fails; skb is NULL\n", __func__);
 			break;
 		}
+		skb_reserve(skb, NET_IP_ALIGN);
 		priv->rx_skbuff[i] = skb;
 		priv->rx_skbuff_dma[i] = dma_map_single(priv->device, skb->data,
 						bfsize, DMA_FROM_DEVICE);
@@ -1401,7 +1403,7 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 	if (priv->plat->enh_desc)
 		max_mtu = JUMBO_LEN;
 	else
-		max_mtu = BUF_SIZE_4KiB;
+		max_mtu = SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN);
 
 	if ((new_mtu < 46) || (new_mtu > max_mtu)) {
 		pr_err("%s: invalid MTU, max MTU is: %d\n", dev->name, max_mtu);
-- 
1.7.4.4

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