aedrix-kernel/kernel/mm.c

#include <list.h>
#include <mm.h>
#include <print.h>

struct dlist_node mm_free_page_list;

void mm_init() {
	init_list(&mm_free_page_list);
}

//presupposes mm_free_page_list is a properly initialized list
void insert_page(struct page *p) {
	if (list_empty(&mm_free_page_list) || p->address < container(mm_free_page_list.next, struct page, list)->address) {
		insert_after(&mm_free_page_list, &p->list);
	} else if (p->address > container(mm_free_page_list.prev, struct page, list)->address) {
		insert_before(&mm_free_page_list, &p->list);
	} else {
		struct page *it;
		for_each_list(it, &mm_free_page_list, struct page, list) {
			if (p->address < it->address) {
				insert_before(&it->list, &p->list);
				return;
			}
		}
		print("Error: failed to insert page\n");
	}
}

void mm_add_free_region(void *start, void *end) {
	unsigned int num_pages, usable_pages;
	struct page *p;
	void *page;

	//make sure both start and end address are aligned to the size of a page
	if ((unsigned int)start % MM_PAGE_SIZE != 0)
		start = (char*)start + (MM_PAGE_SIZE - ((unsigned int)start % MM_PAGE_SIZE));
	if (((unsigned int)end + 1) % MM_PAGE_SIZE != 0)
		end = (char*)end - ((unsigned int)end + 1) % MM_PAGE_SIZE;

	if ((char *)end + 1 - (char *)start < MM_PAGE_SIZE<<1) {
		print("Error: Supplied memory area(%x,%x) is smaller than the page size (%d)\n", (unsigned int)start, (unsigned int)end, MM_PAGE_SIZE);
		return;
	}

	//reserve enough pages at the front of this chunk of memory to hold the
	//page structs, then build the structs and add them to the list

	//TODO we're potentially losing memory here because we're calculating
	//the number of page structs we need even for those pages that will contain only page structs
	num_pages = ((char *)end + 1 - (char *)start) / MM_PAGE_SIZE;
	usable_pages = num_pages - num_pages * sizeof(struct page) / MM_PAGE_SIZE;
	if (num_pages * sizeof(struct page) % MM_PAGE_SIZE)
		usable_pages--;

	p = (struct page *)start;
	for (page = ((char *)start) + (num_pages - usable_pages)*MM_PAGE_SIZE; page < end; page = (void *)(((char *)page) + MM_PAGE_SIZE)) {
		p->address = page;
		insert_page(p);
		p++;
	}
}

struct page* mm_get_free_pages(unsigned int power) {
	unsigned int num_pages = 1<<power;
	struct page *it;

	print("power: %d\n", num_pages);

	if (list_empty(&mm_free_page_list)) {
		print("Error: Out of memory\n");
		return (struct page*)0;
	}

	for_each_list(it, &mm_free_page_list, struct page, list) {
		unsigned int curr_pages = 1;
		struct page *it2;
		for (it2 = container(it->list.next, struct page, list);
					it2->list.next != &mm_free_page_list && curr_pages < num_pages;
					it2 = container(it2->list.next, struct page, list)) {
			if ((char*)it2->address != (char*)container(it2->list.prev, struct page, list)->address + MM_PAGE_SIZE) {
				it = it2; //fast-forward 'it' to start of next contiguous section of pages 
				break;
			} else {
				curr_pages++;
			}
		}
		if (curr_pages == num_pages) {
			remove_splice(&it->list, it2->list.prev);
			return it;
		}
	}
	return (struct page*)0;
}

int mm_put_free_pages(struct page *p) {
	struct page *it;
	for_each_list(it, &mm_free_page_list, struct page, list) {
		if (p->address < it->address) {
			insert_splice_before(&it->list, &p->list, p->list.prev);
			return 0;
		}
	}
	return 1;
}