[net-next,v4,0/6] Improve neigh_flush_dev performance

Message

Gilad Naaman Oct. 15, 2024, 4:59 p.m. UTC

This patchsets improves the performance of neigh_flush_dev.

Currently, the only way to implement it requires traversing
all neighbours known to the kernel, across all network-namespaces.

This means that some flows are slowed down as a function of neighbour-scale,
even if the specific link they're handling has little to no neighbours.

In order to solve this, this patchset adds a netdev->neighbours list,
as well as making the original linked-list doubly-, so that it is
possible to unlink neighbours without traversing the hash-bucket to
obtain the previous neighbour.

The original use-case we encountered was mass-deletion of links (12K
VLANs) while there are 50K ARPs and 50K NDPs in the system; though the
slowdowns would also appear when the links are set down.

Changes in v4:

 - Remove usage of rcu_protected when under lock
 - Rename `list` to a more proper `hash`
 - Divide the patchset into bite-sized commits
 - Remove references to DECnet

Gilad Naaman (6):
  Add hlist_node to struct neighbour
  Define neigh_for_each
  Convert neigh_* seq_file functions to use hlist
  Convert neighbour iteration to use hlist+macro
  Remove bare neighbour::next pointer
  Create netdev->neighbour association

 .../networking/net_cachelines/net_device.rst  |   1 +
 .../ethernet/mellanox/mlxsw/spectrum_router.c |  25 +-
 include/linux/netdevice.h                     |   7 +
 include/net/neighbour.h                       |  29 +-
 include/net/neighbour_tables.h                |  12 +
 net/core/neighbour.c                          | 271 +++++++-----------
 net/mpls/af_mpls.c                            |   2 +-
 7 files changed, 159 insertions(+), 188 deletions(-)
 create mode 100644 include/net/neighbour_tables.h