/*
* 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.
*/
int allocate_frame(pgtbl_entry_t *p) {
int i;
int frame = -1;
for(i = 0; i < memsize; i++) {
if(!coremap[i].in_use) {
frame = i;
break;
}
}
if(frame == -1) { // Didn't find a free page.
// Call replacement algorithm's evict function to select victim
frame = evict_fcn();
// All frames were in use, so victim frame must hold some page
// Write victim page to swap, if needed, and update pagetable
// IMPLEMENTATION NEEDED
// Get the offset and the frame number
int swap_offset = (int) coremap[frame].pte->swap_off;
// Write the victim page into swap
int swap_offset_page = swap_pageout(frame, swap_offset);
assert(swap_offset_page != INVALID_SWAP);
// Update the coremap
coremap[frame].pte->frame =
coremap[frame].pte->frame & ~PG_VALID;
coremap[frame].pte->swap_off = (off_t) swap_offset_page;
coremap[frame].pte->frame =
coremap[frame].pte->frame | PG_ONSWAP;
// Find the dirty bit
unsigned int dirty = coremap[frame].pte->frame & PG_DIRTY;
if (dirty) {
// Increment dirty eviction
evict_dirty_count++;
} else {
evict_clean_count++;
}
}
// Update the page table entry
p->frame = frame << PAGE_SHIFT;
// Record information for virtual page that will now be stored in frame
coremap[frame].in_use = 1;
coremap[frame].pte = p;
return frame;
}
/*
* 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);
}
}
/*
* 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.
*/
int allocate_frame(pgtbl_entry_t *p) {
int i;
int frame = -1;
for(i = 0; i < memsize; i++) {
if(!coremap[i].in_use) {
frame = i;
break;
}
}
if(frame == -1) { // Didn't find a free page.
// Call replacement algorithm's evict function to select victim
frame = evict_fcn();
// All frames were in use, so victim frame must hold some page
// Write victim page to swap, if needed, and update pagetable
// IMPLEMENTATION NEEDED
// Take pte from coremap with given frame
pgtbl_entry_t *pte = coremap[frame].pte;
// Swap old one with the given frame
if(pte->frame & PG_DIRTY){
pte->swap_off = swap_pageout(frame, pte->swap_off);
pte->frame = pte->frame & ~PG_DIRTY;
pte->frame = pte->frame | PG_ONSWAP;
// Increase count for evict_dirty
evict_dirty_count++;
}else{
// Increase count for evict_clean
evict_clean_count++;
}
// Frame is invalid
pte->frame = pte->frame & ~PG_VALID;
}
// Record information for virtual page that will now be stored in frame
coremap[frame].in_use = 1;
coremap[frame].pte = p;
coremap[frame].length = p->length;
return frame;
}
