[Bug 254333] [tcp] sysctl net.inet.tcp.hostcache.list hangs

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254333

--- Comment #17 from Richard Scheffenegger <rscheff at freebsd.org> ---
net.inet.tcp.hostcache.count: 4294966447 is -849 (decimal).

tcp_hc_purge_internal decrements hostcache.count unconditionally, and would be 
the most likely candidate where that counter can rapidely go negative (becoming
a huge uint32).

All the adjustments to hch_length, cache_count and actual add/dels from
hashbuckets appear to be symmetric.

One more hint (more operationally): if you have high "hostcache
buffer-overflows" in 'netstat -snp tcp' you my want to tweak the bucket size
rather than the hashsize.

Unfortunately, the hostcache does not currently provide insight if a wider
hashsize, or a deeper bucketlimit would be preferrential for your workload...

(you would probably want a histogram of #buckets of length "n". If that
histogram shows few deeply used buckets, but most buckets empty or sparsely
used, a narrower hashsize with deeper buckets may be more optimal space use.

If most buckets are mostly used, a wider hashsize may be preferrably over
deeper buckets...

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