Variablesextern bool trimming_cycle;Determines if we are trimming - if we are nearly out of spacestatic page_queue page_free_queue;The queue that holds unused (but not cleared) pagesstatic page_queue page_clear_queue;The queue that holds cleared (0'ed) pagesstatic page_queue page_modified_queue;The queue that holds altered pagesstatic page_queue page_active_queue;The queue that holds in use pages that are not alteredstatic vm_page *all_pages;Every page in the systemstatic addr physical_page_offset;The first address of real ramstatic unsigned int num_pages;Total number of pages in the systemstatic spinlock_t page_lock;A lock to protect the queues.static sem_id modified_pages_available;A semaphore to indicate if there are pages that need to be written to diskstatic void clear_page(addr pa);Sets all values in this page to 0.static vm_page * dequeue_page(page_queue *q)Standard queue remove first page; has count; no lockingvoid dump_page_stats(int argc, char **argv);Dumps counts of each state (active, inactive, busy, not used, modified, free, cleared, wired)void dump_free_page_table(int argc, char **argv)Not done.static void enqueue_page(page_queue *q, vm_page *page)Standard queue add a page; has count; no locking; SPECIAL - for page_modified_queue, if there is only one page modified (new one), release semaphorestatic bool is_page_in_phys_range(kernel_args *ka, addr paddr)Determines if a physical address is in the physical memory that exists.static void move_page_to_queue(page_queue *from_q, page_queue *to_q, vm_page *page)Removes the page from the from_q and adds it to the to_q.static int pageout_daemon()aquires the "modified pages available" semaphore. Gets first page from modified list. Sets it to busy, updates all processes mapping this page that it is no longer a modified page, writes it out to disk, then puts it on the active list (i.e. not modified). Doesn't write out "anonymous" blocks unless we are trimming.static int page_scrubber(void *);Every 1/10 second, takes a page from the free queue, memsets it to 0's, then puts it on the clear queue.static void remove_page_from_queue(page_queue *q, vm_page *page)Removes a given page from the given page queue. No locking.addr vm_alloc_from_ka_struct(kernel_args *ka, unsigned int size, int lock)Gets virtual space in the ka using vm_alloc_vspace_from_ka_struct, then uses vm_alloc_ppage_from_kernel_struct to find a physical page to map it to.static addr vm_alloc_ppage_from_kernel_struct(kernel_args *ka)Attempts to extend, by one page, one of the phys_alloc_range blocks in the kernel args.static addr vm_alloc_vspace_from_ka_struct(kernel_args *ka, unsigned int size)Attempts to find an address range that can be extended to hold size bytes.vm_page * vm_lookup_page(addr page_num)Does the math to get vm_page pointer from a page number.int vm_mark_page_inuse(addr page)Calls vm_mark_page_range_inuse with len of 1.int vm_mark_page_range_inuse(addr start_page, addr len)Sets state to PAGE_STATE_UNUSED for all pages in this range.vm_page * vm_page_allocate_page(int page_state)Gets a single page from the clear or free queue (from page_state), fall back to the other.vm_page * vm_page_allocate_page_run(int page_state, addr len)Attempts to find a run of pages "len" long that are either free or clear. If found, pulls them from their queues and calls vm_page_set_state_nolock on themvm_page * vm_page_allocate_specific_page(addr page_num, int page_state)Finds this page, removes it from the clear or free queue, clears it if necessary and returns. Returns NULL for not found or page in use.int vm_page_init(kernel_args *ka)Initializes the free, clear, modified and active queues. Sets up the vm structures.int vm_page_init2(kernel_args *ka)Properly maps the vm structures allocated in vm_page_init.int vm_page_init_postthread(kernel_args *ka)Creates the page scrubber and the pageout daemon.addr vm_page_num_pages()Returns the total number of pages.addr vm_page_num_free_pages()Returns count of pages in free and clear queues.int vm_page_set_state(vm_page *page, int page_state)Locks, then calls vm_page_set_state_nolock, then unlocks.static int vm_page_set_state_nolock(vm_page *page, int page_state);Moves a page from the state that it is in to the state specified, and moves it from the old queue to the new one.