netdev - Re: [PATCH net-next] neighbor: Add protocol attribute

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Message-ID: <0e223b2f-0677-2450-c75d-1ce18a6c017b@gmail.com>
Date:   Fri, 7 Dec 2018 15:24:05 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, roopa@...ulusnetworks.com
Subject: Re: [PATCH net-next] neighbor: Add protocol attribute

On 12/7/18 3:20 PM, Eric Dumazet wrote:
> 
> 
> On 12/07/2018 01:49 PM, David Ahern wrote:
>> From: David Ahern <dsahern@...il.com>
>>
>> Similar to routes and rules, add protocol attribute to neighbor entries
>> for easier tracking of how each was created.
>>
>> Signed-off-by: David Ahern <dsahern@...il.com>
>> ---
>>  include/net/neighbour.h        |  2 ++
>>  include/uapi/linux/neighbour.h |  1 +
>>  net/core/neighbour.c           | 24 +++++++++++++++++++++++-
>>  3 files changed, 26 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/neighbour.h b/include/net/neighbour.h
>> index 6c13072910ab..e93c59df9501 100644
>> --- a/include/net/neighbour.h
>> +++ b/include/net/neighbour.h
>> @@ -149,6 +149,7 @@ struct neighbour {
>>  	__u8			nud_state;
>>  	__u8			type;
>>  	__u8			dead;
>> +	u8			protocol;
>>  	seqlock_t		ha_lock;
>>  	unsigned char		ha[ALIGN(MAX_ADDR_LEN, sizeof(unsigned long))];
> 
> This looks like ha[] alignment would change, I am not sure how critical it is.

Just adds 4 bytes to neighbour:

...
/* --- cacheline 2 boundary (128 bytes) --- */
long unsigned int          used;                 /*   128     8 */
atomic_t                   probes;               /*   136     4 */
__u8                       flags;                /*   140     1 */
__u8                       nud_state;            /*   141     1 */
__u8                       type;                 /*   142     1 */
__u8                       dead;                 /*   143     1 */
u8                         protocol;             /*   144     1 */

/* XXX 3 bytes hole, try to pack */
seqlock_t                  ha_lock;              /*   148     8 */
unsigned char              ha[32];               /*   156    32 */
/* XXX 4 bytes hole, try to pack */

/* --- cacheline 3 boundary (192 bytes) --- */
struct hh_cache            hh;                   /*   192    48 */

...

but does not change the actual allocation size which is rounded to 512.