[net-next,0/5] net: skbuff: hide some bitfield members

Message

Jakub Kicinski April 14, 2023, 4:01 p.m. UTC

There is a number of protocol or subsystem specific fields
in struct sk_buff which are only accessed by one subsystem.
We can wrap them in ifdefs with minimal code impact.

This gives us a better chance to save a 2B and a 4B holes
resulting with the following savings (assuming a lucky
kernel config):

-	/* size: 232, cachelines: 4, members: 28 */
-	/* sum members: 227, holes: 1, sum holes: 4 */
-	/* sum bitfield members: 8 bits (1 bytes) */
+	/* size: 224, cachelines: 4, members: 28 */
 	/* forced alignments: 2 */
-	/* last cacheline: 40 bytes */
+	/* last cacheline: 32 bytes */

I think that the changes shouldn't be too controversial.
The only one I'm not 100% sure of is the SCTP one,
12 extra LoC for one bit.. But it did fit squarely
in the "this bit has only one user" category.

Jakub Kicinski (5):
  net: skbuff: hide wifi_acked when CONFIG_WIRELESS not set
  net: skbuff: hide csum_not_inet when CONFIG_IP_SCTP not set
  net: skbuff: move alloc_cpu into a potential hole
  net: skbuff: push nf_trace down the bitfield
  net: skbuff: hide nf_trace and ipvs_property

 include/linux/skbuff.h | 38 ++++++++++++++++++++++++++++++++++----
 include/net/sock.h     |  2 +-
 net/core/dev.c         |  3 +--
 net/core/skbuff.c      |  2 ++
 net/sched/act_csum.c   |  3 +--
 net/socket.c           |  2 ++
 6 files changed, 41 insertions(+), 9 deletions(-)

Comments

Eric Dumazet April 15, 2023, 11:53 a.m. UTC | #1

On Fri, Apr 14, 2023 at 6:04 PM Jakub Kicinski <[e-mail]> wrote:
>
> There is a number of protocol or subsystem specific fields
> in struct sk_buff which are only accessed by one subsystem.
> We can wrap them in ifdefs with minimal code impact.
>
> This gives us a better chance to save a 2B and a 4B holes
> resulting with the following savings (assuming a lucky
> kernel config):
>

Reviewed-by: Eric Dumazet <[e-mail]>