neigh_table_shrink_tuner: add tuner to shrink neigh_table size

[Hannibal404]

No description provided.

[alan-maguire]

can you try merging the shrink code into the existing neigh_table_tuner? In general the aim is to coalesce all the tuning for a specific domain into a single tuner. I think it should be pretty straightforward to move the event handling into neigh_table_tuner.c and the bpf code into neigh_table_tuner.bpf.c

[Hannibal404]

I merged them but now I'm seeing the following errors while increasing thresholds when the shrinking part is used first:

Jan 13 15:24:59 prahar-nm bpftune[1106067]: Scenario 'neighbour table grown excessively' occurred for tunable 'net.ipv4.neigh.default.gc_thresh3' in global ns. neighbour table increases are beyond what would be expected for the device given the number of IP addresses/prefixlens associated with it.
Jan 13 15:24:59 prahar-nm bpftune[1106067]: can no longer update thresholds for gc_thresh[1-3] for table 'arp_cache' for device '' (ifindex 0) due to excessive size of table (we computed a reasonable max of 0 based on the prefixlens of the 0 configured addresses). Current thresh1: 12 , thresh2: 51 , thresh3: 102.

It works fine when a call to neigh_create is made first, even if it doesn't trigger a threshold expansion

[Hannibal404]

Hi @alan-maguire , could you take a look when you get the chance? Thanks!

[alan-maguire]

Hi @alan-maguire , could you take a look when you get the chance? Thanks!

yep, looking now, sorry about the delay..

[alan-maguire]

looks great, just would be good to do some code sharing between increase/decrease. also would be good if commit decribed what the tuning does. thanks!

[Hannibal404]

Made the code sharing changes

[alan-maguire]

two small things, but aside from those this looks great to me!