Re: [PATCH v4 net-next] net: neigh: avoid calling neigh_forced_gc on every alloc when table is full

[Jakub Kicinski <kuba@kernel.org>]

On Wed, 15 Jul 2026 05:53:11 +0000 Vimal Agrawal wrote:
> Once the neighbour table exceeds gc_thresh3, neigh_forced_gc() is called
> on every allocation attempt with no rate limiting. In workloads with mostly
> active/reachable entries, the GC walk traverses a large portion of the
> neighbour table without reclaiming entries, holding tbl->lock for an
> extended period. This causes severe lock contention and allocation
> latencies exceeding 16ms under sustained neighbour creation.
> 
> Add a pre-lock check in neigh_forced_gc() to skip the GC run if one was
> performed within the last 50 ms, but only when the table actually contains
> NEIGH_FORCED_GC_LARGE_TABLE_THRESH (16384) or more entries. This avoids
> repeated full table scans and lock acquisitions on the hot allocation path
> while leaving tables with few entries completely unaffected regardless of
> how gc_thresh3 is configured.

Hi Kuniyuki, are you still unconvinced by this?