xv6 memory system

each process can occupy the mempages it needs in xv6.

page management process

kalloc() function apply for a new page

kalloc consume kmem.freelist and kfree return resource back.
freelist is just a linked list with no other info

implement of memset in xv6. we only memeset at alloc part which means all the address has been initialized at the start stage in freelist.

memory initial part

all kmem has been alloced at init stage