I'm replying late, but last night I almost had a complete meltdown of the

I did a partial "pkg upgrade" for the packages that managed to get built by
poudriere, then all hell broke loose. Screen lock-ups, random reboots, and
several hard reboots later I decided to do a fresh buildworld/buildkernel
and we seem to be back at some level of normality. It makes no sense, I
know; and I would not be able to tell you what it was that went wrong.

What I can tell you is that
* While compiling, code would compile for a while, then freeze, then
continue where it left off. "# top -P" was showing that during these
freeze-ups, of the 4 cores on my system, 3 were mostly idle (80% to 95%)
while one core would be at or near 0% idle. Not always the same core, and
when one core got freed-up, you could have another core drop to 0%-8% idle.
I thought maybe radeon was using cpu instead of gpu but that was debunked
when same behavior was observed while compiling my regular kernel without
radeon / xorg loaded.
* Initially a debug-kernel was built with below, but screen goes black when
radeon / xorg is loaded.
(include GENERIC \ ident   KERNDEBUG \ nooptions       INET6 \ options        
KDB \ options         DDB \ options         GDB \ options     INVARIANTS \
options     INVARIANT_SUPPORT \ options     WITNESS \ options    
DEBUG_LOCKS \ options     DEBUG_VFS_LOCKS \ options     DIAGNOSTIC)
* I have modified my zfs-related entries in loader.conf, and latest is:
vfs.zfs.trim.enabled=1         #Enable_Trim
vfs.zfs.prefetch_disable=0   #I have 4G of Ram
#vfs.zfs.arc_min="512M"     #Ram 4GB => 512, Ram 8GB => 1024
#vfs.zfs.arc_max="1536M"   #TotalRam x 0.5 - 512 MB
#vm.kmem_size="6G"          #Ram x 1.5

Currently,  kstat.zfs.misc.arcstats.size: 2012423600 and the number seems to
hang around in that vicinity.

Separate ZFS question then: I have 2 sata-III HDD's (64G SSD + 7200rpm
spindle) and 3 zpools. System is my personal desktop running sql, http
server etc but no commercial load.
tank-b: root, usr, var on SSD
tank-d: home, all data, sql-db, NFS exported PXE root
tank-a: all code compile (poudriere, world), located nearest to the center
of spindle HDD + has 3GB ZIL from SSD drive.

Q1: Is it ok to assume that arcstat.size will not change much regardless of
the number of zpools?
Q2: I have 3GB free space on the SSD reserved for an L2ARC, but decided it
was not necessary after reading that this would be mostly useful for a
commercial web server for example. Was my assessment incorrect and will the
system benefit from a 3GB (or larger?) L2ARC on SSD? If so, which pool (not
sure tank-b makes sense since it's already fully on the same SSD):


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