tmpfs /tmp tmpfs defaults,nosuid,size=1024M,mode=1777 0 0
I'm pretty sure the mount options can be better tweaked. Here is an excerpt from the documentation.
tmpfs has three mount options for sizing: size: The limit of allocated bytes for this tmpfs instance. The default is half of your physical RAM without swap. If you oversize your tmpfs instances the machine will deadlock since the OOM handler will not be able to free that memory. nr_blocks: The same as size, but in blocks of PAGE_CACHE_SIZE. nr_inodes: The maximum number of inodes for this instance. The default is half of the number of your physical RAM pages, or (on a machine with highmem) the number of lowmem RAM pages, whichever is the lower.