The mzap_update() function allocates enough memory for a full
dbuf which can be 128K in size. Ideally, this memory should
be allocated from our slab but in the short term it's simplest
just to vmem_alloc() the memory instead.
Closes#48
Native ZFS for Linux! ZFS is an advanced file system and volume manager
which was originally developed for Solaris. It has been successfully
ported to FreeBSD and now there is a functional Linux ZFS kernel port
too. The port currently includes a fully functional and stable SPA, DMU,
and ZVOL with a ZFS Posix Layer (ZPL) on the way!