ACK: [SRU][N:linux-bluefield][PATCH v1 0/3] UBUNTU: SAUCE: ipv4: Provide a FIB flushing signal from nexthop removal functions

[Alessio Faina]

On Thu, May 07, 2026 at 02:20:15PM +0300, Stav Aviram wrote:
> BugLink: https://bugs.launchpad.net/bugs/2151772
> 
> SRU Justification:
> 
> [IMPACT]
> Fix a performance issue in the IPv4 routing table causing severe RTNL lock
> contention which in some complicated deployments (multiple VXLAN interfaces,
> 128K+ routes, 128K+ nexthops) causes systemd-networkd to fail to renew DHCP
> addresses in time, which then makes those interfaces become unmanaged.
> 
> [FIX]
> The fixes optimize nexthop removal when an interface goes down by batching
> FIB table flushing. Previously, for each nexthop being removed, the FIB table
> was flushed to remove all routing table entries pointing to the nexthop being
> removed. This flushing is a sequential walk of the entire FIB trie, and for N
> nexthops being removed and R routes installed results in O(N x R) performance.
> The fix postpones flushing until all nexthops are marked dead and then does a
> single FIB flush to remove all affected routing entries. This improves the
> performance to O(N + R).
> Upstream patches being submitted here: https://lore.kernel.org/netdev/20260507075606.322405-1-cratiu@nvidia.com/T/#t
> Those patches don't apply cleanly on 6.8 due to other missing functionality, dedicated 6.8. patches will be provided in this ticket.
> 
> [TEST CASE]
> Successfully built the adjusted upstream patches on linux-bluefield-6.8
> master-next branch.
> 
> [Regression Potential]
> Low risk. The latest upstream patches don't apply cleanly on 6.8 due to
> missing functionality, but the modifications to make the patches apply are
> trivial and don't impact the logical flow of batching the cleanup.
> 
> Cosmin Ratiu (3):
>   UBUNTU: SAUCE: ipv4: Provide a FIB flushing signal from nexthop
>     removal functions
>   UBUNTU: SAUCE: ipv4: Flush the FIB once on multiple nexthop removal
>   UBUNTU: SAUCE: ipv4: Add __must_check to nexthop removal functions
> 
>  net/ipv4/nexthop.c | 93 +++++++++++++++++++++++++++++-----------------
>  1 file changed, 58 insertions(+), 35 deletions(-)
> 
> -- 
> 2.38.1
> 
> 
> -- 
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Acked-by: Alessio Faina <alessio.faina at canonical.com>