/*
* 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) {
pgtbl_entry_t *p=NULL; // pointer to the full page table entry for vaddr
unsigned idx = PGDIR_INDEX(vaddr); // get index into page directory
// IMPLEMENTATION NEEDED
// Use top-level page directory to get pointer to 2nd-level page table
if (!(pgdir[idx].pde & PG_VALID)){
pgdir[idx] = init_second_level();
}
// Use vaddr to get index into 2nd-level page table and initialize 'p'
uintptr_t ptr_table = PAGE_MASK & pgdir[idx].pde;
p = (pgtbl_entry_t*)(ptr_table) + PGTBL_INDEX(vaddr);
// Check if p is valid or not, on swap or not, and handle appropriately
// Page is present in the memory
if (p->frame & PG_VALID){
hit_count++;
// Page is not present in the memory
} else {
miss_count++;
ref_count++;
int frame = allocate_frame(p);
// Page on disk.
if (p->frame & PG_ONSWAP){
swap_pagein(frame, p->swap_off);
p->frame = frame << PAGE_SHIFT;
p->frame = p->frame | PG_VALID;
// Page not on disk, first time access the page
} else {
init_frame(frame, vaddr);
p->frame = frame << PAGE_SHIFT;
p->frame = p->frame | PG_DIRTY;
}
}
// Make sure that p is marked valid. Also mark it dirty
// if the access type indicates that the page will be written to
p->frame = p->frame | PG_VALID;
if(type == 'S' || type == 'M'){
p->frame = p->frame | PG_DIRTY;
}
// Call replacement algorithm's ref_fcn for this page
ref_fcn(p);
// p is marked referenced.
p->frame = p->frame | PG_REF;
// Return pointer into (simulated) physical memory at start of frame
return &physmem[(p->frame >> PAGE_SHIFT)*SIMPAGESIZE];
}
/*
* 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) {
pgtbl_entry_t *p=NULL; // pointer to the full page table entry for vaddr
unsigned idx = PGDIR_INDEX(vaddr); // get index into page directory
// IMPLEMENTATION NEEDED
// Use top-level page directory to get pointer to 2nd-level page table
// Check if it's valid
unsigned int valid_pde = pgdir[idx].pde & PG_VALID;
// Not Valid, initialize a 2nd pagetable
if (!valid_pde) {
pgdir[idx] = init_second_level();
}
// Use vaddr to get index into 2nd-level page table and initialize 'p'
unsigned pgtbl_index = PGTBL_INDEX(vaddr);
p = (pgtbl_entry_t *) (pgdir[idx].pde & PAGE_MASK);
p = p + pgtbl_index;
// Check if p is valid or not, on swap or not, and handle appropriately
// Find the valid bit and the on-swap bit
unsigned int valid = p->frame & PG_VALID;
unsigned int on_swap = p->frame & PG_ONSWAP;
// Check if it's valid
if (!valid) {
// Allocate a frame for p
int frame = allocate_frame(p);
// Update fields for OPT
coremap[frame].pgtbl_idx = (int) pgtbl_index;
coremap[frame].pgdir_idx = (int) idx;
// On swap
if (on_swap) {
// Read the page from swap
int success = swap_pagein(frame, p->swap_off);
assert(success == 0);
}
// Not on swap
if (!on_swap) {
// Initialize the frame
init_frame(frame, vaddr);
// Mark it as dirty
p->frame = p->frame | PG_DIRTY;
}
// Not Valid, so increment miss
miss_count++;
}
// Make sure that p is marked valid and referenced. Also mark it
// dirty if the access type indicates that the page will be written to.
// Mark p as valid and referenced
p->frame = p->frame | PG_VALID;
p->frame = p->frame | PG_REF;
unsigned int check = p->frame & PG_VALID;
assert(check);
// Check the access type
if ((type == 'S') || (type == 'M')) {
// Set the dirty bit
p->frame = p->frame | PG_DIRTY;
}
// Increment ref, hit
if (valid) {
hit_count++;
}
ref_count++;
// Call replacement algorithm's ref_fcn for this page
ref_fcn(p);
// Return pointer into (simulated) physical memory at start of frame
return &physmem[(p->frame >> PAGE_SHIFT)*SIMPAGESIZE];
}
