On Thu, Apr 13, 2023 at 06:58:06PM -0700, Abhijeet Rastogi wrote: > Hi Simon, Andrea and Julian, > > I really appreciate you taking the time to respond to my patch. Some follow up > questions that I'll appreciate a response for. > > @Simon Horman > >In any case, I think this patch is an improvement on the current situation. > > +1 to this. I wanted to add that, we're not changing the defaults > here, the default still stays at 2^12. If a kernel user changes the > default, they probably already know what the limitations are, so I > personally don't think it is a big concern. > > @Andrea Claudi > >for the record, RHEL ships with CONFIG_IP_VS_TAB_BITS set to 12 as > default. > > Sorry, I should have been clearer. RHEL ships with the same default, > yes, but it doesn't have the range check, at least, on the version I'm > using right now (3.10.0-1160.62.1.el7.x86_64). > > On this version, I'm able to load with bit size 30, 31 gives me error > regarding allocating memory (64GB host) and anything beyond 31 is > mysteriously switched to a lower number. The following dmesg on my > host confirms that the bitsize 30 worked, which is not possible > without a patch on the current kernel version. > > "[Fri Apr 14 01:14:51 2023] IPVS: Connection hash table configured (size=1073741 > 824, memory=16777216Kbytes)" I see. This makes sense to me as RHEL 7 does not include the range check, while RHEL 8 and RHEL 9 both includes it. The reason why any number beyond 31 results in a lower number is to be searched in gcc implementation. IIRC shifting an int by more than 31 or less than 0 results in an undefined behaviour, according to the C standard. > > @Julian Anastasov, > >This is not a limit of number of connections. I prefer > not to allow value above 24 without adding checks for the > available memory, > > Interesting that you brought up that number 24, that is exactly what > we use in production today. One IPVS node is able to handle spikes of > 10M active connections without issues. This patch idea originated as > my company is migrating from the ancient RHEL version to a somewhat > newer CentOS (5.* kernel) and noticed that we were unable to load the > ip_vs kernel module with anything greater than 20 bits. Another > motivation for kernel upgrade is utilizing maglev to reduce table size > but that's out of context in this discussion. > > My request is, can we increase the range from 20 to something larger? > If 31 seems a bit excessive, maybe, we can settle for something like > [8,30] or even lower. With conn_tab_bits=30, it allocates 16GB at > initialization time, it is not entirely absurd by today's standards. > > I can revise my patch to a lower range as you guys see fit. > > -- > Cheers, > Abhijeet (https://abhi.host) >
