# default\_pmm.c ## 相关练习及分析 * [lab2-练习1](https://oscourse-tsinghua.gitbook.io/ucore-analysis/labs/lab2/practice1) ## default\_pmm.c ```c #include #include #include #include /* In the First Fit algorithm, the allocator keeps a list of free blocks * (known as the free list). Once receiving a allocation request for memory, * it scans along the list for the first block that is large enough to satisfy * the request. If the chosen block is significantly larger than requested, it * is usually splitted, and the remainder will be added into the list as * another free block. * Please refer to Page 196~198, Section 8.2 of Yan Wei Min's Chinese book * "Data Structure -- C programming language". */ // LAB2 EXERCISE 1: YOUR CODE // you should rewrite functions: `default_init`, `default_init_memmap`, // `default_alloc_pages`, `default_free_pages`. /* * Details of FFMA * (1) Preparation: * In order to implement the First-Fit Memory Allocation (FFMA), we should * manage the free memory blocks using a list. The struct `free_area_t` is used * for the management of free memory blocks. * First, you should get familiar with the struct `list` in list.h. Struct * `list` is a simple doubly linked list implementation. You should know how to * USE `list_init`, `list_add`(`list_add_after`), `list_add_before`, `list_del`, * `list_next`, `list_prev`. * There's a tricky method that is to transform a general `list` struct to a * special struct (such as struct `page`), using the following MACROs: `le2page` * (in memlayout.h), (and in future labs: `le2vma` (in vmm.h), `le2proc` (in * proc.h), etc). * (2) `default_init`: * You can reuse the demo `default_init` function to initialize the `free_list` * and set `nr_free` to 0. `free_list` is used to record the free memory blocks. * `nr_free` is the total number of the free memory blocks. * (3) `default_init_memmap`: * CALL GRAPH: `kern_init` --> `pmm_init` --> `page_init` --> `init_memmap` --> * `pmm_manager` --> `init_memmap`. * This function is used to initialize a free block (with parameter `addr_base`, * `page_number`). In order to initialize a free block, firstly, you should * initialize each page (defined in memlayout.h) in this free block. This * procedure includes: * - Setting the bit `PG_property` of `p->flags`, which means this page is * valid. P.S. In function `pmm_init` (in pmm.c), the bit `PG_reserved` of * `p->flags` is already set. * - If this page is free and is not the first page of a free block, * `p->property` should be set to 0. * - If this page is free and is the first page of a free block, `p->property` * should be set to be the total number of pages in the block. * - `p->ref` should be 0, because now `p` is free and has no reference. * After that, We can use `p->page_link` to link this page into `free_list`. * (e.g.: `list_add_before(&free_list, &(p->page_link));` ) * Finally, we should update the sum of the free memory blocks: `nr_free += n`. * (4) `default_alloc_pages`: * Search for the first free block (block size >= n) in the free list and reszie * the block found, returning the address of this block as the address required by * `malloc`. * (4.1) * So you should search the free list like this: * list_entry_t le = &free_list; * while((le=list_next(le)) != &free_list) { * ... * (4.1.1) * In the while loop, get the struct `page` and check if `p->property` * (recording the num of free pages in this block) >= n. * struct Page *p = le2page(le, page_link); * if(p->property >= n){ ... * (4.1.2) * If we find this `p`, it means we've found a free block with its size * >= n, whose first `n` pages can be malloced. Some flag bits of this page * should be set as the following: `PG_reserved = 1`, `PG_property = 0`. * Then, unlink the pages from `free_list`. * (4.1.2.1) * If `p->property > n`, we should re-calculate number of the rest * pages of this free block. (e.g.: `le2page(le,page_link))->property * = p->property - n;`) * (4.1.3) * Re-caluclate `nr_free` (number of the the rest of all free block). * (4.1.4) * return `p`. * (4.2) * If we can not find a free block with its size >=n, then return NULL. * (5) `default_free_pages`: * re-link the pages into the free list, and may merge small free blocks into * the big ones. * (5.1) * According to the base address of the withdrawed blocks, search the free * list for its correct position (with address from low to high), and insert * the pages. (May use `list_next`, `le2page`, `list_add_before`) * (5.2) * Reset the fields of the pages, such as `p->ref` and `p->flags` (PageProperty) * (5.3) * Try to merge blocks at lower or higher addresses. Notice: This should * change some pages' `p->property` correctly. */ free_area_t free_area; #define free_list (free_area.free_list) #define nr_free (free_area.nr_free) static void default_init(void) { list_init(&free_list); nr_free = 0; } static void default_init_memmap(struct Page *base, size_t n) { assert(n > 0); struct Page *p = base; for (; p != base + n; p ++) { assert(PageReserved(p)); p->flags = p->property = 0; set_page_ref(p, 0); } base->property = n; SetPageProperty(base); nr_free += n; list_add_before(&free_list, &(base->page_link)); } static struct Page * default_alloc_pages(size_t n) { assert(n > 0); if (n > nr_free) { return NULL; } struct Page *page = NULL; list_entry_t *le = &free_list; // TODO: optimize (next-fit) while ((le = list_next(le)) != &free_list) { struct Page *p = le2page(le, page_link); if (p->property >= n) { page = p; break; } } if (page != NULL) { if (page->property > n) { struct Page *p = page + n; p->property = page->property - n; SetPageProperty(p); list_add_after(&(page->page_link), &(p->page_link)); } list_del(&(page->page_link)); nr_free -= n; ClearPageProperty(page); } return page; } static void default_free_pages(struct Page *base, size_t n) { assert(n > 0); struct Page *p = base; for (; p != base + n; p ++) { assert(!PageReserved(p) && !PageProperty(p)); p->flags = 0; set_page_ref(p, 0); } base->property = n; SetPageProperty(base); list_entry_t *le = list_next(&free_list); while (le != &free_list) { p = le2page(le, page_link); le = list_next(le); // TODO: optimize if (base + base->property == p) { base->property += p->property; ClearPageProperty(p); list_del(&(p->page_link)); } else if (p + p->property == base) { p->property += base->property; ClearPageProperty(base); base = p; list_del(&(p->page_link)); } } nr_free += n; le = list_next(&free_list); while (le != &free_list) { p = le2page(le, page_link); if (base + base->property <= p) { assert(base + base->property != p); break; } le = list_next(le); } list_add_before(le, &(base->page_link)); } static size_t default_nr_free_pages(void) { return nr_free; } static void basic_check(void) { struct Page *p0, *p1, *p2; p0 = p1 = p2 = NULL; assert((p0 = alloc_page()) != NULL); assert((p1 = alloc_page()) != NULL); assert((p2 = alloc_page()) != NULL); assert(p0 != p1 && p0 != p2 && p1 != p2); assert(page_ref(p0) == 0 && page_ref(p1) == 0 && page_ref(p2) == 0); assert(page2pa(p0) < npage * PGSIZE); assert(page2pa(p1) < npage * PGSIZE); assert(page2pa(p2) < npage * PGSIZE); list_entry_t free_list_store = free_list; list_init(&free_list); assert(list_empty(&free_list)); unsigned int nr_free_store = nr_free; nr_free = 0; assert(alloc_page() == NULL); free_page(p0); free_page(p1); free_page(p2); assert(nr_free == 3); assert((p0 = alloc_page()) != NULL); assert((p1 = alloc_page()) != NULL); assert((p2 = alloc_page()) != NULL); assert(alloc_page() == NULL); free_page(p0); assert(!list_empty(&free_list)); struct Page *p; assert((p = alloc_page()) == p0); assert(alloc_page() == NULL); assert(nr_free == 0); free_list = free_list_store; nr_free = nr_free_store; free_page(p); free_page(p1); free_page(p2); } // LAB2: below code is used to check the first fit allocation algorithm (your EXERCISE 1) // NOTICE: You SHOULD NOT CHANGE basic_check, default_check functions! static void default_check(void) { int count = 0, total = 0; list_entry_t *le = &free_list; while ((le = list_next(le)) != &free_list) { struct Page *p = le2page(le, page_link); assert(PageProperty(p)); count ++, total += p->property; } assert(total == nr_free_pages()); basic_check(); struct Page *p0 = alloc_pages(5), *p1, *p2; assert(p0 != NULL); assert(!PageProperty(p0)); list_entry_t free_list_store = free_list; list_init(&free_list); assert(list_empty(&free_list)); assert(alloc_page() == NULL); unsigned int nr_free_store = nr_free; nr_free = 0; free_pages(p0 + 2, 3); assert(alloc_pages(4) == NULL); assert(PageProperty(p0 + 2) && p0[2].property == 3); assert((p1 = alloc_pages(3)) != NULL); assert(alloc_page() == NULL); assert(p0 + 2 == p1); p2 = p0 + 1; free_page(p0); free_pages(p1, 3); assert(PageProperty(p0) && p0->property == 1); assert(PageProperty(p1) && p1->property == 3); assert((p0 = alloc_page()) == p2 - 1); free_page(p0); assert((p0 = alloc_pages(2)) == p2 + 1); free_pages(p0, 2); free_page(p2); assert((p0 = alloc_pages(5)) != NULL); assert(alloc_page() == NULL); assert(nr_free == 0); nr_free = nr_free_store; free_list = free_list_store; free_pages(p0, 5); le = &free_list; while ((le = list_next(le)) != &free_list) { struct Page *p = le2page(le, page_link); count --, total -= p->property; } assert(count == 0); assert(total == 0); } const struct pmm_manager default_pmm_manager = { .name = "default_pmm_manager", .init = default_init, .init_memmap = default_init_memmap, .alloc_pages = default_alloc_pages, .free_pages = default_free_pages, .nr_free_pages = default_nr_free_pages, .check = default_check, }; ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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