poudriere: swap_pager: out of swap space

hi list,

i'm having a recurring problem with poudriere that i hope someone might
have an idea about.

i'm building packages with poudriere on a system with 32GB memory, with
tmpfs and md disabled in poudriere (so it's using ZFS only) and with the
ZFS ARC limited to 8GB.

running poudriere produces many kernel log messages like this:

Jan 10 21:40:00 ilythia kernel: swap_pager: out of swap space
Jan 10 21:40:00 ilythia kernel: swp_pager_getswapspace(2): failed
Jan 10 22:41:55 ilythia kernel: swap_pager: out of swap space
Jan 10 22:41:55 ilythia kernel: swp_pager_getswapspace(21): failed
Jan 10 23:48:03 ilythia kernel: swap_pager: out of swap space
Jan 10 23:48:03 ilythia kernel: swp_pager_getswapspace(8): failed
Jan 11 00:05:00 ilythia kernel: swp_pager_getswapspace(1): failed
Jan 11 00:21:45 ilythia kernel: swp_pager_getswapspace(10): failed

this is despite the system having a large amount of "Inact" memory
according to top(1):

Mem: 3828M Active, 15G Inact, 2921M Laundry, 9263M Wired, 1559M Buf, 892M Free
ARC: 3113M Total, 994M MFU, 884M MRU, 39M Anon, 49M Header, 1139M Other
     1296M Compressed, 4130M Uncompressed, 3.19:1 Ratio
Swap: 2048M Total, 2048M Used, 8192B Free, 99% Inuse

from what i can tell, these swap errors don't cause any issues with the
poudriere build, but they do seem to hinder interactive usage by causing
long hangs.

does anyone have some idea what's going on here?  i don't really
understand why the system has used 100% of available swap space when it
has plenty of Inact memory it could free to fulfill requirements.