From 5cf26522a591f0b82060c24519e911a0d2fb7651 Mon Sep 17 00:00:00 2001
From: KAAAsS <admin@kaaass.net>
Date: Thu, 13 May 2021 00:18:55 +0800
Subject: [PATCH] finish buddy

---
 lab2/kernel/mm/buddy.c | 105 +++++++++++++++++++++++++++++++++++++----
 note.org               |  12 +++++
 2 files changed, 108 insertions(+), 9 deletions(-)

diff --git a/lab2/kernel/mm/buddy.c b/lab2/kernel/mm/buddy.c
index 88b680b..c8cac33 100644
--- a/lab2/kernel/mm/buddy.c
+++ b/lab2/kernel/mm/buddy.c
@@ -26,7 +26,7 @@ void init_buddy(struct phys_mem_pool *pool, struct page *start_page,
     /* 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));
+        init_list_head(&(pool->free_lists[order].free_list));  // free lists 初始化为空链表
     }
 
     /* Clear the page_metadata area. */
@@ -35,17 +35,20 @@ void init_buddy(struct phys_mem_pool *pool, struct page *start_page,
     /* Init the page_metadata area. */
     for (page_idx = 0; page_idx < page_num; ++page_idx) {
         page = start_page + page_idx;
-        page->allocated = 1;
+        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);
+        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;
@@ -87,8 +90,31 @@ static struct page *get_buddy_chunk(struct phys_mem_pool *pool,
 static struct page *split_page(struct phys_mem_pool *pool, u64 order,
                                struct page *page) {
     // <lab2>
-    struct page *split_page = NULL;
-    return split_page;
+    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>
 }
 
@@ -97,12 +123,29 @@ static struct page *split_page(struct phys_mem_pool *pool, u64 order,
  * pool @ physical memory structure reserved in the kernel
  * order @ get the (1<<order) continous pages from the buddy system
  *
- * Hints: Find the corresonding free_list which can allocate 1<<order
+ * 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;
+    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>
@@ -120,8 +163,41 @@ struct page *buddy_get_pages(struct phys_mem_pool *pool, u64 order) {
 static struct page *merge_page(struct phys_mem_pool *pool, struct page *page) {
     // <lab2>
 
-    struct page *merge_page = NULL;
-    return merge_page;
+    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
+    struct page *t;
+    if (buddy < page) {
+        t = 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>
 }
 
@@ -135,6 +211,17 @@ static struct page *merge_page(struct phys_mem_pool *pool, struct page *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>
 }
 
diff --git a/note.org b/note.org
index 86cdb27..b0c6817 100644
--- a/note.org
+++ b/note.org
@@ -94,4 +94,16 @@ LR
 
 ** Lab 2
 
+*** 问题1：哪个文件或代码段中指定了 ChCore 物理内存布局
 
+**** 编译阶段
+
+编译时配置镜像格式的文件为 scripts/linker-aarch64.lds.in
+
+**** 运行阶段
+
+运行阶段在 kernel/mm.c:L70 的 mm_init 设置各个地址
+
+*** 练习1
+
+基本思路就是回收的时候一路尝试向上合并，分配的时候找一个更大的块然后一路向下分裂。