One page or 4 percent of physical memory, whichever is greater.
Number of bytes in one page (8192 for sun4u or sun4v systems, 4096 for all other systems) to 25 percent of the available kernel memory at the time TMPFS was first used.
Increase if the following message is displayed on the console or written in the messages file:
tmp_memalloc: tmpfs over memory limit
The current amount of memory used by TMPFS for its data structures is held in the tmp_kmemspace field. This field can be examined with a kernel debugger.