Re: [PATCH net v4 1/1] ipmr: account multicast table and route memory

[Ido Schimmel]

On Tue, Sep 08, 2026 at 11:58:39AM +0000, Zihan Xi wrote:
> A netadmin in a user+net namespace can create many IPv4 and IPv6
> multicast routing tables with MRT_TABLE and MRT6_TABLE. Each unseen
> id allocates an mr_table via the shared mr_table_alloc(), links it
> into the per-net list, and leaves it until netns teardown. Those
> objects were not charged to memcg, so the host unreclaimable slab
> grows with the table count.
> 
> Account mr_table allocations with GFP_KERNEL_ACCOUNT and mark the
> IPv4/IPv6 MFC caches SLAB_ACCOUNT. This matches the established
> handling of IP addresses, routes and alternate interface names.
> 
> Unresolved MFC entries are still allocated from softIRQ with
> GFP_ATOMIC and are not charged. They expire after 10 seconds and are
> bounded by the socket receive queue; see commit 0079ad8e8dc3
> ("ipmr: remove hard code cache_resolve_queue_len limit").

Not worth a v5, just noting in case Sashiko nit picks on it:

Unresolved MFC entries can be allocated from process context and in this
case they are charged correctly.

> 
> Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
> Fixes: d1db275dd3f6 ("ipv6: ip6mr: support multiple tables")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Vega <vega@xxxxxxxxxx>
> Assisted-by: LLM
> Signed-off-by: Zihan Xi <zihanx@xxxxxxxxxx>

Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxx>