IPVS: conn_tab_bits param for ip_vs > 20 leads to default being set

IPVS: conn_tab_bits param for ip_vs > 20 leads to default being set

[Abhijeet Rastogi]

Hi IPVS users,

This behavior is on the 5.4 CentOS kernel and should be because of
this check. As per the commit message[1], the problematic value is
when conn_tab_bits>31. With that in mind, why do we limit the size to
7 < conn_tab_bits < 21?

I stumbled upon this problem while upgrading our production hosts from
old RHEL with kernel 3.10 to CentOS with kernel 5.4. On current RHEL
systems, conn_tab_bits=24 works just fine.

# RHEL output:-
$ sudo ipvsadm -Ln|head -n1
IP Virtual Server version 1.2.1 (size=16777216)

Sidenote: lvs-users mailing list is dead since 2020, but it is still
listed on the LVS website.
http://www.linuxvirtualserver.org/mailing.html

[1]: https://github.com/torvalds/linux/commit/69e73dbfda14fbfe748d3812da1244cce2928dcb

Cheers,
Abhijeet (https://abhi.host)

Re: IPVS: conn_tab_bits param for ip_vs > 20 leads to default being set

[Abhijeet Rastogi]

Hi everyone,

I'll really appreciate some help, I felt this is the best forum to
discuss this topic. If not, please suggest.

I understand that the Kconfig file also has 8-20 range, but why isn't
that range set higher, let's say 31?

Thank you,
Abhijeet

On Mon, Feb 6, 2023 at 2:48 PM Abhijeet Rastogi <abhijeet.1989@gmail.com> wrote:
>
> Hi IPVS users,
>
> This behavior is on the 5.4 CentOS kernel and should be because of
> this check. As per the commit message[1], the problematic value is
> when conn_tab_bits>31. With that in mind, why do we limit the size to
> 7 < conn_tab_bits < 21?
>
> I stumbled upon this problem while upgrading our production hosts from
> old RHEL with kernel 3.10 to CentOS with kernel 5.4. On current RHEL
> systems, conn_tab_bits=24 works just fine.
>
> # RHEL output:-
> $ sudo ipvsadm -Ln|head -n1
> IP Virtual Server version 1.2.1 (size=16777216)
>
> Sidenote: lvs-users mailing list is dead since 2020, but it is still
> listed on the LVS website.
> http://www.linuxvirtualserver.org/mailing.html
>
> [1]: https://github.com/torvalds/linux/commit/69e73dbfda14fbfe748d3812da1244cce2928dcb
>
> Cheers,
> Abhijeet (https://abhi.host)



-- 
Cheers,
Abhijeet (https://abhi.host)

Re: IPVS: conn_tab_bits param for ip_vs > 20 leads to default being set

[Florian Westphal]

Abhijeet Rastogi <abhijeet.1989@gmail.com> wrote:
> Hi everyone,
> 
> I'll really appreciate some help, I felt this is the best forum to
> discuss this topic. If not, please suggest.
> 
> I understand that the Kconfig file also has 8-20 range, but why isn't
> that range set higher, let's say 31?

You could send a patch to increase the limit in both kconfig and the
check.

The 20 bit (1m entries) ceiling exists since the original merge of ipvs
in 2003, so likely this was just considered "big enough" back then.