Re: [PATCH] ipvs: change ip_vs_conn_tab_bits range to [8,31]

[Julian Anastasov <ja@xxxxxx>]

        Hello,

On Wed, 12 Apr 2023, Abhijeet Rastogi via B4 Relay wrote:

> From: Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>
> 
> Current range [8, 20] is set purely due to historical reasons
> because at the time, ~1M (2^20) was considered sufficient.
> 
> Previous change regarding this limit is here.
> 
> Link: 
> https://lore.kernel.org/all/86eabeb9dd62aebf1e2533926fdd13fed48bab1f.1631289960.git.aclaudi@xxxxxxxxxx/T/#u
> 
> Signed-off-by: Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>
> ---
> The conversation for this started at: 
> 
> https://www.spinics.net/lists/netfilter/msg60995.html
> 
> The upper limit for algo is any bit size less than 32, so this
> change will allow us to set bit size > 20. Today, it is common to have
> RAM available to handle greater than 2^20 connections per-host.

        This is not a limit of number of connections. I prefer
not to allow value above 24 without adding checks for the
available memory, this more concern for 32-bit. Blindly
allocating 2^20 (1048576 pointers which is 8MB) should not
cause OOM but selecting large value and then using this
kernel on boxes with less memory is dangerous.

> Distros like RHEL already have higher limits set.
> ---
>  net/netfilter/ipvs/Kconfig      | 4 ++--
>  net/netfilter/ipvs/ip_vs_conn.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/netfilter/ipvs/Kconfig b/net/netfilter/ipvs/Kconfig
> index 271da8447b29..3e3371f8c0f9 100644
> --- a/net/netfilter/ipvs/Kconfig
> +++ b/net/netfilter/ipvs/Kconfig
> @@ -44,7 +44,7 @@ config      IP_VS_DEBUG
>  
>  config       IP_VS_TAB_BITS
>       int "IPVS connection table size (the Nth power of 2)"
> -     range 8 20
> +     range 8 31
>       default 12
>       help
>         The IPVS connection hash table uses the chaining scheme to handle
> @@ -54,7 +54,7 @@ config      IP_VS_TAB_BITS
>  
>         Note the table size must be power of 2. The table size will be the
>         value of 2 to the your input number power. The number to choose is
> -       from 8 to 20, the default number is 12, which means the table size
> +       from 8 to 31, the default number is 12, which means the table size
>         is 4096. Don't input the number too small, otherwise you will lose
>         performance on it. You can adapt the table size yourself, according
>         to your virtual server application. It is good to set the table size
> diff --git a/net/netfilter/ipvs/ip_vs_conn.c b/net/netfilter/ipvs/ip_vs_conn.c
> index 13534e02346c..bc0fe1a698d4 100644
> --- a/net/netfilter/ipvs/ip_vs_conn.c
> +++ b/net/netfilter/ipvs/ip_vs_conn.c
> @@ -1484,8 +1484,8 @@ int __init ip_vs_conn_init(void)
>       int idx;
>  
>       /* Compute size and mask */
> -     if (ip_vs_conn_tab_bits < 8 || ip_vs_conn_tab_bits > 20) {
> -             pr_info("conn_tab_bits not in [8, 20]. Using default value\n");
> +     if (ip_vs_conn_tab_bits < 8 || ip_vs_conn_tab_bits > 31) {
> +             pr_info("conn_tab_bits not in [8, 31]. Using default value\n");
>               ip_vs_conn_tab_bits = CONFIG_IP_VS_TAB_BITS;
>       }
>       ip_vs_conn_tab_size = 1 << ip_vs_conn_tab_bits;
> 
> ---
> base-commit: 09a9639e56c01c7a00d6c0ca63f4c7c41abe075d
> change-id: 20230412-increase_ipvs_conn_tab_bits-4322c90da216
> 
> Best regards,
> -- 
> Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>

Regards

--
Julian Anastasov <ja@xxxxxx>