[PINTOS PROJECT 3] VIRTUAL MEMORY_Memory management

Implement SPT

1. supplement_page_table_init()

• process.c/ initd() 에서 호출
• hash table 자료구조 활용하여 spt 생성

void
supplemental_page_table_init (struct supplemental_page_table *spt UNUSED) {
	struct hash* page_table = malloc(sizeof (struct hash));
	hash_init (page_table, page_hash, page_less, NULL);
	spt -> page_table = page_table;
}

2. spt_find_page()

• 인자로 받은 va로 spt에서 해당 page를 찾아 반환

struct page *  
spt_find_page (struct supplemental_page_table *spt, void *va) {
	struct page page;
	page.va = pg_round_down (va);
	struct hash_elem *e = hash_find (spt -> page_table, &page.hash_elem);
	if (e == NULL) return NULL;
	struct page* result = hash_entry (e, struct page, hash_elem);
	ASSERT((va < result -> va + PGSIZE) && va >= result -> va);
	return result;
}

3. spt_insert_page()

• 최초 processs 실행/ 실행 중 exe / 실행 중 fork / 실행 중 mmap()에서 호출

bool
spt_insert_page (struct supplemental_page_table *spt,
		struct page *page) {
	struct hash_elem *result= hash_insert (spt -> page_table, &page -> hash_elem);
	return (result == NULL) ? true : false ;
}

Frame Management

1. vm_get_frame()

1) frame 구조체 생성
2) frame -> kva = palloc 할당 받기
3) frame -> kva = NULL (할당 실패시)
--> vm_evict_frame() -> vm_get_victim() -> swap_out() -> return victim
--> 제거할 page를 제거한 상태의 frame 구조체(사용가능한 frame)

static struct frame *
vm_get_frame (void) {
	struct frame * frame = malloc (sizeof (struct frame));
	frame -> kva = palloc_get_page (PAL_USER);
	frame -> page = NULL;
	ASSERT (frame != NULL);
	ASSERT (frame->page == NULL);
	// Add swap case handling
	if (frame->kva == NULL) {
	  free (frame);
	  frame = vm_evict_frame ();
	}
	ASSERT (frame->kva != NULL);
	return frame;
}

2. vm_do_claim_page()

1) vm_get_frame() 통해 frame 생성
2) frame <-> page 연결
3) insert page table entry to map page's VA to frmae's PA

static bool
vm_do_claim_page (struct page *page) {
	struct frame *frame = vm_get_frame ();  /*Physical address와의 connection*/
	struct thread *curr = thread_current ();

	ASSERT (frame != NULL);
	ASSERT (page != NULL);

	/* Set links */
	frame->page = page;
	page->frame = frame;
	
	// Add to frame_list for eviction clock algorithm
	if (clock_elem != NULL)
		// Just before current clock
		list_insert (clock_elem, &frame->elem);
	else
		list_push_back (&frame_list, &frame->elem);

	/*Insert page table entry to map page's VA to frame's PA. */
	if (!pml4_set_page (curr -> pml4, page -> va, frame->kva, page -> writable))
		return false;
	return swap_in (page, frame->kva);
}

3. vm_claim_page()

1) page 구조체 선언
2) spt_find_page()로 함수 인자로 받은 va에 해당하는 페이지를 spt에서 찾아 반환
3) vm_do_claim_page() 호출

bool
vm_claim_page (void *va UNUSED) {
	struct page *page = spt_find_page (&thread_current () ->spt, va);
	if (page == NULL) return false;
	return vm_do_claim_page (page);
}