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pagetable.c
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pagetable.c
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#include <assert.h>
#include <string.h>
#include "sim.h"
#include "pagetable.h"
// The top-level page table (also known as the 'page directory')
pgdir_entry_t pgdir[PTRS_PER_PGDIR]; //4096个,也就是4k个一级索引
// Counters for various events.
// Your code must increment these when the related events occur.
int hit_count = 0;
int miss_count = 0;
int ref_count = 0;
int evict_clean_count = 0;
int evict_dirty_count = 0;
////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////
/*
* Allocates a frame to be used for the virtual page represented by p.
* If all frames are in use, calls the replacement algorithm's evict_fcn to
* select a victim frame. Writes victim to swap if needed, and updates
* pagetable entry for victim to indicate that virtual page is no longer in
* (simulated) physical memory.
*
* Counters for evictions should be updated appropriately in this function.
*
* @param: second-level page table entry pointer
* @return: frame number
*/
int allocate_frame(pgtbl_entry_t *p) {
int fn = -1;
int i;
// select frame from physical memory
for(i = 0; i < memsize; i++)
{
if(!coremap[i].in_use)
{
fn = i;
break;
}
}
// If all frame is in used, use schedule algorithm to select a frame
if(fn == -1)
{
fn = evict_fcn();
pgtbl_entry_t *victim = coremap[fn].pte;
off_t swap_off = victim->swap_off;
victim->frame &= (~PG_VALID);
// counting
if((victim->frame & PG_DIRTY)) evict_dirty_count++;
else evict_clean_count++;
// evicted and dirty page should be written to swap file
if(!(victim->frame & PG_ONSWAP) || (victim->frame & PG_DIRTY))
{
victim->frame &= (~PG_DIRTY);
off_t ret_off = swap_pageout((victim->frame)>>PAGE_SHIFT, swap_off);
if(ret_off != -1)
{
victim->swap_off = ret_off;
}
else
{
perror("swap_pageout error\n");
fprintf(stderr, "not on swap error");
exit(1);
}
}
}
// coremap record for debug
coremap[fn].in_use = 1;
coremap[fn].pte = p;
return fn;
}
/*
* Initializes the top-level pagetable.
* This function is called once at the start of the simulation.
* For the simulation, there is a single "process" whose reference trace is
* being simulated, so there is just one top-level page table (page directory).
* To keep things simple, we use a global array of 'page directory entries'.
*
* In a real OS, each process would have its own page directory, which would
* need to be allocated and initialized as part of process creation.
*/
void init_pagetable() {
int i;
// Set all entries in top-level pagetable to 0, which ensures valid
// bits are all 0 initially.
for (i=0; i < PTRS_PER_PGDIR; i++) {
pgdir[i].pde = 0;
}
}
// For simulation, we get second-level pagetables from ordinary memory
// 二级目录初始化,对应malloc出一个table entry的数组,默认是PTRS_PER_PGTBL = 4096大小的,初始化所有元素的frame是0保证invalid,swap位也设置为0
pgdir_entry_t init_second_level() {
int i;
pgtbl_entry_t *pgtbl;
pgdir_entry_t new_entry;
// Allocating aligned memory ensures the low bits in the pointer must
// be zero, so we can use them to store our status bits, like PG_VALID
// 利用对齐可以使我们利用指针的低位
if (posix_memalign((void **)&pgtbl, PAGE_SIZE,
PTRS_PER_PGTBL*sizeof(pgtbl_entry_t)) != 0) {
perror("Failed to allocate aligned memory for page table");
exit(1);
}
for(i = 0; i < PTRS_PER_PGTBL; i++)
{
pgtbl[i].frame = 0;
pgtbl[i].swap_off = INVALID_SWAP;
}
new_entry.pde = (uintptr_t)pgtbl | PG_VALID;
return new_entry;
}
/*
* Initializes the content of a (simulated) physical memory frame when it
* is first allocated for some virtual address. Just like in a real OS,
* we fill the frame with zero's to prevent leaking information across
* pages.
*
* In our simulation, we also store the the virtual address itself in the
* page frame to help with error checking.
*
*/
// 初始化frame,将给定下标为frame的physical memory所有bytes设为0,并且用coremap绑定好virtual memory
// 到底是frame_number还是frame?
void init_frame(int frame_num, addr_t vaddr) {
char *mem_ptr = &physmem[frame_num * SIMPAGESIZE];
addr_t *vaddr_ptr = (addr_t *)(mem_ptr + sizeof(int));
memset(mem_ptr, 0, SIMPAGESIZE);
*vaddr_ptr = vaddr;
}
/*
* Locate the physical frame number for the given vaddr using the page table.
*
* If the entry is invalid and not on swap, then this is the first reference
* to the page and a (simulated) physical frame should be allocated and
* initialized (using init_frame).
*
* If the entry is invalid and on swap, then a (simulated) physical frame
* should be allocated and filled by reading the page data from swap.
*
* Counters for hit, miss and reference events should be incremented in
* this function.
*/
char *find_physpage(addr_t vaddr, char type) {
}
////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////
void print_pagetbl(pgtbl_entry_t *pgtbl) {
int i;
int first_invalid, last_invalid;
first_invalid = last_invalid = -1;
for (i=0; i < PTRS_PER_PGTBL; i++) {
if (!(pgtbl[i].frame & PG_VALID) &&
!(pgtbl[i].frame & PG_ONSWAP)) {
if (first_invalid == -1) {
first_invalid = i;
}
last_invalid = i;
} else {
if (first_invalid != -1) {
printf("\t[%d] - [%d]: INVALID\n",
first_invalid, last_invalid);
first_invalid = last_invalid = -1;
}
printf("\t[%d]: ",i);
if (pgtbl[i].frame & PG_VALID) {
printf("VALID, ");
if (pgtbl[i].frame & PG_DIRTY) {
printf("DIRTY, ");
}
printf("in frame %d\n",pgtbl[i].frame >> PAGE_SHIFT);
} else {
assert(pgtbl[i].frame & PG_ONSWAP);
printf("ONSWAP, at offset %lu\n",pgtbl[i].swap_off);
}
}
}
if (first_invalid != -1) {
printf("\t[%d] - [%d]: INVALID\n", first_invalid, last_invalid);
first_invalid = last_invalid = -1;
}
}
void print_pagedirectory() {
int i; // index into pgdir
int first_invalid,last_invalid;
first_invalid = last_invalid = -1;
pgtbl_entry_t *pgtbl;
for (i=0; i < PTRS_PER_PGDIR; i++) {
if (!(pgdir[i].pde & PG_VALID)) {
if (first_invalid == -1) {
first_invalid = i;
}
last_invalid = i;
} else {
if (first_invalid != -1) {
printf("[%d]: INVALID\n to\n[%d]: INVALID\n",
first_invalid, last_invalid);
first_invalid = last_invalid = -1;
}
pgtbl = (pgtbl_entry_t *)(pgdir[i].pde & PAGE_MASK);
printf("[%d]: %p\n",i, pgtbl);
print_pagetbl(pgtbl);
}
}
}