ChCore-exercise/lab5/kernel/mm/buddy.c

#include <common/util.h>
#include <common/macro.h>
#include <common/kprint.h>

#include "buddy.h"

/*
 * The layout of a phys_mem_pool:
 * | page_metadata are (an array of struct page) | alignment pad | usable memory |
 *
 * The usable memory: [pool_start_addr, pool_start_addr + pool_mem_size).
 */
void init_buddy(struct phys_mem_pool *pool, struct page *start_page,
                vaddr_t start_addr, u64 page_num) {
    int order;
    int page_idx;
    struct page *page;

    /* Init the physical memory pool. */
    pool->pool_start_addr = start_addr;
    pool->page_metadata = start_page;
    pool->pool_mem_size = page_num * BUDDY_PAGE_SIZE;
    /* This field is for unit test only. */
    pool->pool_phys_page_num = page_num;

    /* Init the free lists */
    for (order = 0; order < BUDDY_MAX_ORDER; ++order) {
        pool->free_lists[order].nr_free = 0;
        init_list_head(&(pool->free_lists[order].free_list));  // free lists 初始化为空链表
    }

    /* Clear the page_metadata area. */
    memset((char *) start_page, 0, page_num * sizeof(struct page));

    /* Init the page_metadata area. */
    for (page_idx = 0; page_idx < page_num; ++page_idx) {
        page = start_page + page_idx;
        page->allocated = 1;  // 所有页面初始化为已分配
        page->order = 0;
    }

    /* Put each physical memory page into the free lists. */
    for (page_idx = 0; page_idx < page_num; ++page_idx) {
        page = start_page + page_idx;
        buddy_free_pages(pool, page);  // 逐一去配页面以初始化 free lists
    }
}

/*
 * 获得页面的伙伴页面
 */
static struct page *get_buddy_chunk(struct phys_mem_pool *pool,
                                    struct page *chunk) {
    u64 chunk_addr;
    u64 buddy_chunk_addr;
    int order;

    /* Get the address of the chunk. */
    chunk_addr = (u64) page_to_virt(pool, chunk);
    order = chunk->order;
    /*
     * Calculate the address of the buddy chunk according to the address
     * relationship between buddies.
     */
#define BUDDY_PAGE_SIZE_ORDER (12)
    buddy_chunk_addr = chunk_addr ^
                       (1UL << (order + BUDDY_PAGE_SIZE_ORDER));

    /* Check whether the buddy_chunk_addr belongs to pool. */
    if ((buddy_chunk_addr < pool->pool_start_addr) ||
        (buddy_chunk_addr >= (pool->pool_start_addr +
                              pool->pool_mem_size))) {
        return NULL;
    }

    return virt_to_page(pool, (void *) buddy_chunk_addr);
}

/*
 * split_page: split the memory block into two smaller sub-block, whose order
 * is half of the origin page.
 * pool @ physical memory structure reserved in the kernel
 * order @ order for origin page block
 * page @ splitted page
 *
 * Hints: don't forget to substract the free page number for the corresponding free_list.
 * you can invoke split_page recursively until the given page can not be splitted into two
 * smaller sub-pages.
 */
static struct page *split_page(struct phys_mem_pool *pool, u64 order,
                               struct page *page) {
    // <lab2>
    struct page *buddy = NULL;

    // 我理解的这个函数：把 page 递归切成 order，返回结果。过程修改的都是未分配区域。

    // 递归出口
    if (page->order == order) {
        return page;
    } else if (page->order < order) {
        return NULL;
    }
    // 分裂
    // 删除当前节点
    list_del(&page->node);
    pool->free_lists[page->order].nr_free--;
    // 降格
    page->order--;
    // 找伙伴
    buddy = get_buddy_chunk(pool, page);
    buddy->order = page->order;
    // 加入 free list
    list_add(&page->node, &pool->free_lists[page->order].free_list);
    list_add(&buddy->node, &pool->free_lists[page->order].free_list);
    pool->free_lists[page->order].nr_free += 2;
    // 递归调用
    return split_page(pool, order, page);
    // </lab2>
}

/*
 * buddy_get_pages: get free page from buddy system.
 * pool @ physical memory structure reserved in the kernel
 * order @ get the (1<<order) continous pages from the buddy system
 *
 * Hints: Find the corresponding free_list which can allocate 1<<order
 * continuous pages and don't forget to split the list node after allocation
 */
struct page *buddy_get_pages(struct phys_mem_pool *pool, u64 order) {
    // <lab2>
    struct page *page = NULL, *free_page = NULL;

    // 找可分配 order
    u64 free_order = order;
    while (free_order < BUDDY_MAX_ORDER && pool->free_lists[free_order].nr_free == 0) {
        free_order++;
    }
    // 当前无可分配
    if (free_order == BUDDY_MAX_ORDER) {
        return NULL;
    }
    // 有可分配，取一块切分
    free_page = (struct page *) pool->free_lists[free_order].free_list.next;
    page = split_page(pool, order, free_page);
    // 删除出 free list，分配
    list_del(&page->node);
    pool->free_lists[page->order].nr_free--;
    page->allocated = true;

    return page;
    // </lab2>
}

/*
 * merge_page: merge the given page with the buddy page
 * pool @ physical memory structure reserved in the kernel
 * page @ merged page (attempted)
 *
 * Hints: you can invoke the merge_page recursively until
 * there is not corresponding buddy page. get_buddy_chunk
 * is helpful in this function.
 */
static struct page *merge_page(struct phys_mem_pool *pool, struct page *page) {
    // <lab2>

    struct page *try_merge = NULL, *buddy = get_buddy_chunk(pool, page);

    // 不存在伙伴、伙伴已分配、order 不同则无法合并
    if (buddy == NULL || buddy->allocated || page->order != buddy->order) {
        return NULL;
    }
    // 如果已经最大 order，则不合并
    if (page->order >= BUDDY_MAX_ORDER - 1) {
        return NULL;
    }

    // 双方都未分配，可以合并一次
    // 从 free 中删除两个节点
    list_del(&page->node);
    list_del(&buddy->node);
    pool->free_lists[page->order].nr_free -= 2;
    // 选择左侧 page
    if (buddy < page) {
        page = buddy;
    }
    // 增加 page 的 order
    page->order++;
    // 链入上一层空列表
    list_add(&page->node, &pool->free_lists[page->order].free_list);
    pool->free_lists[page->order].nr_free++;
    // 尝试递归合并
    try_merge = merge_page(pool, page);
    if (try_merge != NULL) {
        return try_merge;
    }

    return page;

    // </lab2>
}

/*
 * buddy_free_pages: give back the pages to buddy system
 * pool @ physical memory structure reserved in the kernel
 * page @ free page structure
 *
 * Hints: you can invoke merge_page.
 */
void buddy_free_pages(struct phys_mem_pool *pool, struct page *page) {
    // <lab2>

    if (!page->allocated)
        return;

    // 设置标志
    page->allocated = false;
    // 修改 free list
    list_add(&page->node, &pool->free_lists[page->order].free_list);
    pool->free_lists[page->order].nr_free++;
    // 尝试合并当前页面
    merge_page(pool, page);

    // </lab2>
}

void *page_to_virt(struct phys_mem_pool *pool, struct page *page) {
    u64 addr;

    /* page_idx * BUDDY_PAGE_SIZE + start_addr */
    addr = (page - pool->page_metadata) * BUDDY_PAGE_SIZE +
           pool->pool_start_addr;
    return (void *) addr;
}

struct page *virt_to_page(struct phys_mem_pool *pool, void *addr) {
    struct page *page;

    page = pool->page_metadata +
           (((u64) addr - pool->pool_start_addr) / BUDDY_PAGE_SIZE);
    return page;
}

u64 get_free_mem_size_from_buddy(struct phys_mem_pool *pool) {
    int order;
    struct free_list *list;
    u64 current_order_size;
    u64 total_size = 0;

    for (order = 0; order < BUDDY_MAX_ORDER; order++) {
        /* 2^order * 4K */
        current_order_size = BUDDY_PAGE_SIZE * (1 << order);
        list = pool->free_lists + order;
        total_size += list->nr_free * current_order_size;

        /* debug : print info about current order */
        kdebug("buddy memory chunk order: %d, size: 0x%lx, num: %d\n",
               order, current_order_size, list->nr_free);
    }
    return total_size;
}