Re: [PATCH 06/24] net, diet: Use small UDP hash tables on small kernels

Eric Dumazet
2014-05-06T14:26:46Z

On Mon, 2014-05-05 at 15:25 -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> UDP has two hash tables, for UDP and UDP lite. Default
> them to 16 entries each on small kernels. This can be
> still overriden on the command line.
>
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
> net/ipv4/udp.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 4468e1a..90f967b 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2415,7 +2415,12 @@ void udp4_proc_exit(void)
> }
> #endif /* CONFIG_PROC_FS */
>
> +#ifdef CONFIG_BASE_SMALL
> +static __initdata unsigned long uhash_entries = 16;
> +#else
> static __initdata unsigned long uhash_entries;
> +#endif
> +
> static int __init set_uhash_entries(char *str)
> {
> ssize_t ret;

Its changed to UDP_HTABLE_SIZE_MIN later in alloc_large_system_hash()

The reason there is a minimum UDP hash size is PORTS_PER_CHAIN,
or DECLARE_BITMAP(bitmap, PORTS_PER_CHAIN) on stack.

This patch has no effect on a small machine, because we already
dynamically size this hash table.

(The factor is one slot per 2MB of low memory)