Yesterday, testing multiprocess Firefox 55.0.2 with dom.ipc.processCount
set to 20
(more than the content process limit of 7
that's permissible through about:preferences
):

β whilst using poudriere with PARALLEL_JOBS=2
on the four-processor notebook to build x11/kde. Significant use of swap, performance was OK.
Today, whilst building www/firefox (preparing to install 55.0.3) I have hit the content process limit of 20, again there's significant use of swap, performance is greatβ¦
1 [|||||||||||||||||||||||| 58.6%] Tasks: 170, 0 thr, 33 kthr; 8 running
2 [||||||||||||||||||||||||| 61.3%] Load average: 3.83 4.16 4.96
3 [|||||||||||||||||||||||||||| 70.2%] Uptime: 01:40:27
4 [|||||||||||||||||||||||||||| 70.7%]
Mem[||||||||||||||||||||||||||||9.67G/15.9G]
Swp[|||||||||||||||||| 3.63G/8.00G]
S PID USER PRI NI VIRT RES S CPU% MEM% TIME+ Command
S 1745 grahamper 25 0 3877M 2046M S 12.0 12.6 42:24.93 firefox
R 1882 grahamper 31 0 7707M 1183M R 19.1 7.3 11:45.64 seamonkey
R 1775 grahamper 91 0 1947M 633M R 68.3 3.9 58:05.35 firefox -contentproc -childID 3 -isForBr
R 1847 grahamper 86 0 1887M 593M R 47.7 3.6 39:50.15 firefox -contentproc -childID 30 -isForB
S 1853 grahamper 20 0 1873M 590M S 0.0 3.6 3:10.67 firefox -contentproc -childID 33 -isForB
S 1846 grahamper 20 0 1732M 522M S 0.0 3.2 2:19.44 firefox -contentproc -childID 29 -isForB
S 1856 grahamper 20 0 1784M 514M S 0.0 3.2 3:46.48 firefox -contentproc -childID 34 -isForB
S 1496 grahamper 20 0 938M 507M S 3.8 3.1 2:28.85 kwin_x11 -session 1037131636631300015018
S 1851 grahamper 20 0 1788M 502M S 0.9 3.1 4:38.98 firefox -contentproc -childID 32 -isForB
S 1844 grahamper 21 0 1761M 487M S 1.9 3.0 5:56.02 firefox -contentproc -childID 28 -isForB
S 1848 grahamper 22 0 1655M 444M S 2.1 2.7 3:06.20 firefox -contentproc -childID 31 -isForB
S 1834 grahamper 20 0 1617M 415M S 0.0 2.6 2:49.58 firefox -contentproc -childID 23 -isForB
S 1805 grahamper 20 0 1635M 395M S 0.0 2.4 2:46.46 firefox -contentproc -childID 18 -isForB
S 1828 grahamper 20 0 1608M 358M S 0.0 2.2 1:31.28 firefox -contentproc -childID 21 -isForB
S 1819 grahamper 20 0 1632M 357M S 0.0 2.2 2:58.18 thunderbird
S 1842 grahamper 20 0 1612M 352M S 0.0 2.2 2:11.45 firefox -contentproc -childID 27 -isForB
S 1836 grahamper 20 0 1607M 351M S 0.0 2.2 1:56.94 firefox -contentproc -childID 24 -isForB
S 1807 grahamper 20 0 1578M 346M S 0.1 2.1 1:57.61 firefox -contentproc -childID 19 -isForB
S 1857 grahamper 20 0 1597M 345M S 0.0 2.1 1:51.81 firefox -contentproc -childID 35 -isForB
S 1840 grahamper 20 0 1593M 336M S 0.0 2.1 1:44.96 firefox -contentproc -childID 26 -isForB
S 1803 grahamper 20 0 1574M 325M S 0.0 2.0 1:39.09 firefox -contentproc -childID 17 -isForB
S 1838 grahamper 20 0 1501M 281M S 0.0 1.7 1:39.34 firefox -contentproc -childID 25 -isForB
S 1832 grahamper 20 0 1540M 278M S 0.7 1.7 15:28.85 firefox -contentproc -childID 22 -isForB
S 1817 grahamper 20 0 1450M 199M S 0.0 1.2 1:41.52 firefox -contentproc -childID 20 -isForB
S 1306 root 21 0 253M 158M S 3.8 1.0 5:58.10 X -nolisten tcp -auth /var/run/sddm/{9e4
S 1502 grahamper 26 0 521M 149M S 12.1 0.9 6:48.31 plasmashell
R 66836 nobody 81 0 160M 123M R 31.2 0.8 0:03.69 c++ -cc1 -triple x86_64-unknown-freebsd1
S 62840 grahamper 20 0 191M 80788 S 0.0 0.5 0:01.43 kinfocenter
S 1760 grahamper 20 0 256G 76644 S 0.0 0.5 0:14.00 dolphin
S 1809 grahamper 20 0 195M 69692 S 4.1 0.4 0:45.45 konsole
S 59449 grahamper 20 0 95532 57864 S 0.0 0.3 0:01.18 eom /home/grahamperrin/Pictures/2017-08-