default_pmm.c
相关练习及分析
default_pmm.c
#include <pmm.h>
#include <list.h>
#include <string.h>
#include <default_pmm.h>
/* 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,
};Last updated