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

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Date:	Tue, 8 Apr 2008 09:22:53 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Linux Netdev List <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-2.6.26 2/2] Do not allocate unneeded memory for
	dev->priv alignment.

On Tue, Apr 08, 2008 at 12:42:27PM +0400, Pavel Emelyanov wrote:
> Jarek Poplawski wrote:
> > Pavel Emelyanov wrote, On 04/07/2008 06:31 PM:
> > ...
> > 
> >> ---
> >>  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) {
> > 
> > 
> > IMHO this second "+ NETDEV_ALIGN_CONST" is needed here because of "~NETDEV_ALIGN_CONST".
> 
> Hmm, AFAIC, the net_device alignment is done earlier, while this one
> makes sense in case the priv pointer alignment.

Hmm, one NETDEV_ALIGN_CONST is later used just for net_device alignment,
and you could not fit this struct after "~NETDEV_ALIGN_CONST" without
adding anything. So you should probably skip "~NETDEV_ALIGN_CONST" in
this no priv case too?

Jarek P.
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