MAXPHYS is to small for the modern program, it is not enough even
for print process memory map.
To avoid this, limit storage size of the sbuf buffer by tunable sysctl.
Why do you need a sysctl ? If bumping, simply increase to some larger but reasonable value, e.g. 2M. IOSIZE_MAX is definitely unreasonable.
Seems like the limit could be removed by using an sbuf drain function?