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

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

[Pavel Emelyanov]

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@openvz.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

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

[Jarek Poplawski]

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".

Regards,
Jarek P.

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

[Pavel Emelyanov]

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.

> Regards,
> Jarek P.
> 

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

[Jarek Poplawski]

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.

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

[David Miller]

From: Jarek Poplawski <jarkao2@gmail.com>
Date: Tue, 8 Apr 2008 09:22:53 +0000

> On Tue, Apr 08, 2008 at 12:42:27PM +0400, Pavel Emelyanov wrote:
> > 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?

The Linux NETDEV Patch Robot has determined that these other
NETDEV_ALIGN_CONST instances need to be retained, therefore
Pavel's patch will be applied to net-2.6.26.

*beep* *beep*

Thank you for your valuable feedback.

*beep* *beep*

Keep hacking.