When calling zpool import, zpool does a few ioctls to ZFS.
zpool allocates a buffer in userland and passes it to the kernel so that ZFS
can copy info into it. ZFS will use it to put the nvlist that describes the
pool configuration.
If the allocated buffer is too small, ZFS will return ENOMEM and the call will
have to be redone. This wastes CPU time and slows down the import process. This
happens very often for the ZFS_IOC_POOL_TRYIMPORT call.