[PATCH net-next v2 0/8] netconsole: stop charging netpoll users for netconsole-only data

[Breno Leitao <leitao@debian.org>]

This work continue to untangle netconsole and netpoll, improving
memory usage for netpoll users that are not netconsole.

struct netpoll is shared by every netpoll consumer in the tree:
bonding, bridge, team, vlan, macvlan, dsa and netconsole. The non-
netconsole users only need a per-port handle that lets them transmit
SKBs.

Yet struct netpoll has accumulated a pile of fields that exist only
to serve netconsole's printk path:

  - skb_pool / refill_wq: the fallback skb pool find_skb() falls back
    on when alloc_skb() returns NULL, plus the workqueue that refills
    it.
  - local_port / remote_port / remote_mac: the source and destination
    UDP ports and the destination ethernet address used to build
    outgoing log packets.

Every netpoll user that allocates a struct netpoll pays for all of
these fields, even though it never queues a single skb on the pool,
never sends a UDP frame and never looks at any of the addressing.

Move this netconsole-only state out of the shared struct into struct
netconsole_target, where its only consumer already lives.

After the series every passive netpoll consumer drops
sizeof(sk_buff_head) + sizeof(work_struct) + 2 * sizeof(u16) +
ETH_ALEN bytes per port (plus padding), and struct netpoll keeps only
what belongs to the generic poll/transmit abstraction or what netpoll
core still reads itself.

Follow-ups
----------

local_ip, remote_ip and ipv6 are still in struct netpoll. Moving the
addressing additionally requires relocating netpoll_setup() -- whose
only caller is netconsole -- and its IPv4/IPv6 helpers, so it is left
for a follow-up to keep this series focused on a single responsibility
transfer.

This is pure code motion with no functional change. The pre-existing
target/device teardown races reported against v1 have since been fixed
independently (as suggested by Jakub) and are already in the tree, so,
re-posting this one.

Changes in v2:
- Rebase on net-next, now that the prerequisite netconsole
  teardown-race fixes are merged.
- Squash the local_port and remote_port moves into a single patch.
- v1: https://lore.kernel.org/r/20260524-netconsole_move_more-v1-0-909d1ab398b4@debian.org

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Breno Leitao (8):
      netpoll: export refill_skbs(), refill_skbs_work_handler(), skb_pool_flush()
      netconsole: take over skb pool lifecycle from netpoll
      netconsole: move refill_skbs_work_handler() from netpoll
      netconsole: move refill_skbs() and skb-pool sizing macros from netpoll
      netconsole: move skb_pool_flush() from netpoll
      netconsole: move skb_pool / refill_wq from struct netpoll to netconsole_target
      netconsole: move local_port / remote_port from struct netpoll to netconsole_target
      netconsole: move remote_mac from struct netpoll to netconsole_target

 drivers/net/netconsole.c | 184 ++++++++++++++++++++++++++++++++++++-----------
 include/linux/netpoll.h  |  18 -----
 net/core/netpoll.c       |  51 +------------
 3 files changed, 144 insertions(+), 109 deletions(-)
---
base-commit: 1c664ec4b9ea827b609d296921ed5bad8a40a158
change-id: 20260514-netconsole_move_more-888fde03dfc7

Best regards,
-- 
Breno Leitao <leitao@debian.org>