netdev - Re: [PATCH net-next] net/dst: use a smaller percpu_counter batch for dst entries accounting

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Message-ID: <20200508222019.0f6319b6@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 8 May 2020 22:20:19 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] net/dst: use a smaller percpu_counter batch
 for dst entries accounting

On Thu,  7 May 2020 18:58:10 -0700 Eric Dumazet wrote:
> percpu_counter_add() uses a default batch size which is quite big
> on platforms with 256 cpus. (2*256 -> 512)
> 
> This means dst_entries_get_fast() can be off by +/- 2*(nr_cpus^2)
> (131072 on servers with 256 cpus)
> 
> Reduce the batch size to something more reasonable, and
> add logic to ip6_dst_gc() to call dst_entries_get_slow()
> before calling the _very_ expensive fib6_run_gc() function.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thank you!