netdev - [PATCH net-2.6.26 2/2] Do not allocate unneeded memory for dev->priv alignment.

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Date:	Mon, 07 Apr 2008 20:31:12 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Linux Netdev List <netdev@...r.kernel.org>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	Patrick McHardy <kaber@...sh.net>
Subject: [PATCH net-2.6.26 2/2] Do not allocate unneeded memory for dev->priv
 alignment.

The alloc_netdev_mq() tries to produce 32-bytes alignment for both
the net_device itself and its private data. The second alignment is
achieved by adding the NETDEV_ALIGN_CONST to the whole size of
the memory to be allocated.

However, for those devices that do not need the private area, this
addition just makes the net_device weight 1024 + 32 = 1068 bytes,
i.e. consume twice as much memory.

Since loopback device is such (sizeof_priv == 0 for it), and each
net namespace creates one, this can save a noticeable amount of
memory for kernel with net namespaces turned on.

After this set the lo device is actually allocated from a size-1024
kmem cache on i386 box even with NETPOLL and WIRELESS_EXT turned on.

Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

---
 net/core/dev.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 7aa0112..80e103a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4000,7 +4000,8 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 	alloc_size = (sizeof(*dev) + NETDEV_ALIGN_CONST +
 		     (sizeof(struct net_device_subqueue) * (queue_count - 1))) &
 		     ~NETDEV_ALIGN_CONST;
-	alloc_size += sizeof_priv + NETDEV_ALIGN_CONST;
+	if (sizeof_priv)
+		alloc_size += sizeof_priv + NETDEV_ALIGN_CONST;

 	p = kzalloc(alloc_size, GFP_KERNEL);
 	if (!p) {
-- 
1.5.3.4

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