netdev - Re: [PATCH bpf] bpf: Improve bucket

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Message-ID: <20200207130721.pitlvbxcx656c7ur@ltop.local>
Date:   Fri, 7 Feb 2020 14:07:21 +0100
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>, kernel-team@...com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux-Sparse <linux-sparse@...r.kernel.org>,
        netdev@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH bpf] bpf: Improve bucket_log calculation logic

On Fri, Feb 07, 2020 at 12:18:10AM -0800, Martin KaFai Lau wrote:
> 
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index 458be6b3eda9..3ab23f698221 100644
> --- a/net/core/bpf_sk_storage.c
> +++ b/net/core/bpf_sk_storage.c
> @@ -643,9 +643,10 @@ static struct bpf_map *bpf_sk_storage_map_alloc(union bpf_attr *attr)
>  		return ERR_PTR(-ENOMEM);
>  	bpf_map_init_from_attr(&smap->map, attr);
>  
> +	nbuckets = roundup_pow_of_two(num_possible_cpus());
>  	/* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
> -	smap->bucket_log = max_t(u32, 1, ilog2(roundup_pow_of_two(num_possible_cpus())));
> -	nbuckets = 1U << smap->bucket_log;
> +	nbuckets = max_t(u32, 2, nbuckets);
> +	smap->bucket_log = ilog2(nbuckets);
>  	cost = sizeof(*smap->buckets) * nbuckets + sizeof(*smap);
>  
>  	ret = bpf_map_charge_init(&smap->map.memory, cost);
> -- 

Yes, that's much nicer to read. Feel free to add my

Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@...il.com>

-- Luc