ZFS - Always Out of Memory
Solution 1:
ZFS also uses a lot of SLAB space in the kernel. You can check how much SLAB it is using by either checking /proc/meminfo or by installing nmon.
More detailed information about slab usage can be found under /proc/slabinfo and /proc/spl/kmem/slab
It's worth reading this to understand more about the memory usage of ZFS.