netdev - [PATCH net-next] net: allow large number of tx queues

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Date:	Thu, 20 Jun 2013 01:15:51 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Jason Wang <jasowang@...hat.com>, davem@...emloft.net,
	hkchu@...gle.com, netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] net: allow large number of tx queues

From: Eric Dumazet <edumazet@...gle.com>

On Wed, 2013-06-19 at 21:07 +0300, Michael S. Tsirkin wrote:

> As we have explicit code to recover, maybe set __GFP_NOWARN?
> If we are out of memory, vzalloc will warn too, we don't
> need two warnings.

Yes, that's absolutely the right thing to do.

Its yet not clear this patch is really needed, but here it is.

Thanks

[PATCH net-next] net: allow large number of tx queues

netif_alloc_netdev_queues() uses kcalloc() to allocate memory
for the "struct netdev_queue *_tx" array.

For large number of tx queues, kcalloc() might fail, so this
patch does a fallback to vzalloc().

As vmalloc() adds overhead on a critical network path, add __GFP_REPEAT
to kzalloc() flags to do this fallback only when really needed.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c |   26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index fa007db..722f633 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -130,6 +130,7 @@
 #include <linux/cpu_rmap.h>
 #include <linux/static_key.h>
 #include <linux/hashtable.h>
+#include <linux/vmalloc.h>
 
 #include "net-sysfs.h"
 
@@ -5253,17 +5254,28 @@ static void netdev_init_one_queue(struct net_device *dev,
 #endif
 }
 
+static void netif_free_tx_queues(struct net_device *dev)
+{
+	if (is_vmalloc_addr(dev->_tx))
+		vfree(dev->_tx);
+	else
+		kfree(dev->_tx);
+}
+
 static int netif_alloc_netdev_queues(struct net_device *dev)
 {
 	unsigned int count = dev->num_tx_queues;
 	struct netdev_queue *tx;
+	size_t sz = count * sizeof(*tx);
 
-	BUG_ON(count < 1);
-
-	tx = kcalloc(count, sizeof(struct netdev_queue), GFP_KERNEL);
-	if (!tx)
-		return -ENOMEM;
+	BUG_ON(count < 1 || count > 0xffff);
 
+	tx = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
+	if (!tx) {
+		tx = vzalloc(sz);
+		if (!tx)
+			return -ENOMEM;
+	}
 	dev->_tx = tx;
 
 	netdev_for_each_tx_queue(dev, netdev_init_one_queue, NULL);
@@ -5811,7 +5823,7 @@ free_all:
 
 free_pcpu:
 	free_percpu(dev->pcpu_refcnt);
-	kfree(dev->_tx);
+	netif_free_tx_queues(dev);
 #ifdef CONFIG_RPS
 	kfree(dev->_rx);
 #endif
@@ -5836,7 +5848,7 @@ void free_netdev(struct net_device *dev)
 
 	release_net(dev_net(dev));
 
-	kfree(dev->_tx);
+	netif_free_tx_queues(dev);
 #ifdef CONFIG_RPS
 	kfree(dev->_rx);
 #endif


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