Re: [PATCHv3 net 1/2] fib: convert fib_nh_is_v6 and nh_updated to use a single bit

[David Ahern <dsahern@kernel.org>]

On 9/21/23 7:29 PM, Hangbin Liu wrote:
> On Thu, Sep 21, 2023 at 07:03:20AM -0600, David Ahern wrote:
>> On 9/20/23 9:14 PM, Hangbin Liu wrote:
>>> The FIB info structure currently looks like this:
>>> struct fib_info {
>>>         struct hlist_node          fib_hash;             /*     0    16 */
>>>         [...]
>>>         u32                        fib_priority;         /*    80     4 */
>>>
>>>         /* XXX 4 bytes hole, try to pack */
>>>
>>>         struct dst_metrics *       fib_metrics;          /*    88     8 */
>>>         int                        fib_nhs;              /*    96     4 */
>>>         bool                       fib_nh_is_v6;         /*   100     1 */
>>>         bool                       nh_updated;           /*   101     1 */
>>>
>>>         /* XXX 2 bytes hole, try to pack */
>>
>> 2B hole here and you want to add a single flag so another bool. I would
>> prefer the delay to a bitfield until all holes are consumed.
>>
> 
> OK, just in case I didn't misunderstand. I should add a `bool pfsrc_removed`
> here and drop the first patch, right?


yes.

The bitfield has higher overhead. Let's reserve that overhead to when
there are no more holes and a new field pushes the struct over 128B.