netdev - Re: [PATCH net-next 1/2] mlxsw: spectrum_router: Add trap adjacency entry upon first nexthop group

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Date:   Wed, 22 Sep 2021 10:43:52 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        jiri@...dia.com, mlxsw@...dia.com, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/2] mlxsw: spectrum_router: Add trap adjacency
 entry upon first nexthop group

Wed, Sep 22, 2021 at 09:36:41AM CEST, idosch@...sch.org wrote:
>From: Ido Schimmel <idosch@...dia.com>
>
>In commit 0c3cbbf96def ("mlxsw: Add specific trap for packets routed via
>invalid nexthops"), mlxsw started allocating a new adjacency entry
>during driver initialization, to trap packets routed via invalid
>nexthops.
>
>This behavior was later altered in commit 983db6198f0d ("mlxsw:
>spectrum_router: Allocate discard adjacency entry when needed") to only
>allocate the entry upon the first route that requires it. The motivation
>for the change is explained in the commit message.
>
>The problem with the current behavior is that the entry shows up as a
>"leak" in a new BPF resource monitoring tool [1]. This is caused by the
>asymmetry of the allocation/free scheme. While the entry is allocated
>upon the first route that requires it, it is only freed during
>de-initialization of the driver.
>
>Instead, track the number of active nexthop groups and allocate the
>adjacency entry upon the creation of the first group. Free it when the
>number of active groups reaches zero.
>
>The next patch will convert mlxsw to start using the new entry and
>remove the old one.
>
>[1] https://github.com/Mellanox/mlxsw/tree/master/Debugging/libbpf-tools/resmon
>
>Signed-off-by: Ido Schimmel <idosch@...dia.com>

Reviewed-by: Jiri Pirko <jiri@...dia.com>