The _1 and _2 parameter names are not typical in FreeBSD. I would suggest sticking with void *arg for the first argument and int flags for the second argument.

IMHO, better to use meaningful names for arguments even though they aren't used:

foo_lowmem(void *ctx __unused, int flags __unused)

Heh, ctx would be ok as well. void *arg is a pretty common idiom in FreeBSD for callback arguments where the entity registering a callback gets to pass through an opaque argument to the callback (which is what the first arguments to event handlers are).