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Maintain a reference to the frame allocated in the SPT

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This commit is contained in:
sBubshait
2024-12-06 02:15:51 +00:00
parent b2b3f77a91
commit e047e7aa45
4 changed files with 164 additions and 177 deletions
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5
src/userprog/exception.c
View File

@@ -262,7 +262,12 @@ fetch_page (void *upage, bool write)
bool writeable = pagedir_is_writable (t->pagedir, upage);
if (pagedir_set_page (t->pagedir, upage, kpage, writeable))
{
struct page_entry *page = page_get(upage);
if (page != NULL)
page->frame = kpage;
return true;
}
}
/* Check if the page is in the supplemental page table. That is, it is a page

323
src/vm/frame.c
View File

@@ -2,7 +2,7 @@
#include <hash.h>
#include <list.h>
#include <string.h>
#include <stdio.h>
#include "frame.h"
#include "page.h"
#include "threads/malloc.h"
@@ -11,151 +11,117 @@
#include "threads/synch.h"
#include "devices/swap.h"
/* Hash table that maps every active frame's kernel virtual address
to its corresponding 'frame_metadata'.*/
struct frame_entry
{
void *frame;
void *upage;
struct thread *owner;
bool pinned;
struct hash_elem hash_elem;
struct list_elem list_elem;
};
struct hash frame_table;
/* Linked list used to represent the circular queue in the 'clock'
algorithm for page eviction. Iterating from the element that is
currently pointed at by 'next_victim' yields an ordering of the entries
from oldest to newest (in terms of when they were added or checked
for having been referenced by a process). */
struct lock frame_lock;
struct list lru_list;
struct list_elem *next_victim;
/* The next element in lru_list to be considered for eviction (oldest added
or referenced page in the circular queue). If this page has has an
'accessed' bit of 0 when considering eviction, then it will be the next
victim. Otherwise, the next element in the queue is similarly considered. */
struct list_elem *next_victim = NULL;
/* Synchronisation variables. */
/* Protects access to 'lru_list'. */
struct lock lru_lock;
struct frame_metadata
{
void *frame; /* The kernel virtual address holding the frame. */
void *upage; /* The user virtual address pointing to the frame. */
struct thread *owner; /* Pointer to the thread that owns the frame. */
bool pinned;
struct hash_elem hash_elem; /* Tracks the position of the frame metadata
within 'frame_table', whose key is the
kernel virtual address of the frame. */
struct list_elem list_elem; /* Tracks the position of the frame metadata
in either the 'active' or 'inactive' list,
so a victim can be chosen for eviction. */
};
hash_hash_func frame_metadata_hash;
hash_less_func frame_metadata_less;
hash_hash_func frame_hash;
hash_less_func frame_less;
static struct frame_entry *frame_get (void *frame);
static struct frame_entry *get_victim (void);
static struct list_elem *lru_next (struct list_elem *e);
static struct list_elem *lru_prev (struct list_elem *e);
static struct frame_metadata *frame_metadata_get (void *frame);
static struct frame_metadata *get_victim (void);
/* Initialize the frame system by initializing the frame (hash) table with
the frame_metadata hashing and comparison functions, as well as initializing
'lru_list' and its associated synchronisation primitives. */
void
frame_init (void)
{
hash_init (&frame_table, frame_metadata_hash, frame_metadata_less, NULL);
hash_init (&frame_table, frame_hash, frame_less, NULL);
lock_init (&frame_lock);
list_init (&lru_list);
lock_init (&lru_lock);
}
/* TODO: Consider synchronisation more closely (i.e. just for hash
table). */
/* Attempt to allocate a frame for a user process, either by direct
allocation of a user page if there is sufficient RAM, or by
evicting a currently active page if memory allocated for user
processes is fulled and storing it in swap. If swap is full in
the former case, panic the kernel. */
void *
frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
{
struct frame_metadata *frame_metadata;
lock_acquire (&frame_lock);
struct frame_entry *frame_metadata;
flags |= PAL_USER;
lock_acquire (&lru_lock);
void *frame = palloc_get_page (flags);
/* If a frame couldn't be allocated we must be out of main memory. Thus,
obtain a victim page to replace with our page, and swap the victim
into disk. */
if (frame == NULL)
{
/* 1. Obtain victim. */
if (next_victim == NULL)
PANIC ("Couldn't allocate a single page to main memory!\n");
{
if (next_victim == NULL)
PANIC ("Couldn't allocate a single page to main memory!\n");
struct frame_metadata *victim = get_victim ();
ASSERT (victim != NULL); /* get_victim () should never return null. */
struct frame_entry *victim = get_victim ();
ASSERT (victim != NULL); /* get_victim () should never return null. */
/* 2. Swap out victim into disk. */
/* Mark page as 'not present' and flag the page directory as having
been modified *before* eviction begins to prevent the owner of the
victim page from accessing/modifying it mid-eviction. */
pagedir_clear_page (victim->owner->pagedir, victim->upage);
/* 2. Swap out victim into disk. */
/* Mark page as 'not present' and flag the page directory as having
been modified *before* eviction begins to prevent the owner of the
victim page from accessing/modifying it mid-eviction. */
pagedir_clear_page (victim->owner->pagedir, victim->upage);
// TODO: Lock PTE of victim page for victim process.
// TODO: Lock PTE of victim page for victim process.
size_t swap_slot = swap_out (victim->frame);
page_set_swap (victim->owner, victim->upage, swap_slot);
size_t swap_slot = swap_out (victim->frame);
page_set_swap (victim->owner, victim->upage, swap_slot);
/* If zero flag is set, zero out the victim page. */
if (flags & PAL_ZERO)
memset (victim->frame, 0, PGSIZE);
/* If zero flag is set, zero out the victim page. */
if (flags & PAL_ZERO)
memset (victim->frame, 0, PGSIZE);
/* 3. Indicate that the new frame's metadata will be stored
inside the same structure that stored the victim's metadata.
As both the new frame and the victim frame share the same kernel
virtual address, the hash map need not be updated, and neither
the list_elem value as both share the same lru_list position. */
frame_metadata = victim;
}
/* 3. Indicate that the new frame's metadata will be stored
inside the same structure that stored the victim's metadata.
As both the new frame and the victim frame share the same kernel
virtual address, the hash map need not be updated, and neither
the list_elem value as both share the same lru_list position. */
frame_metadata = victim;
}
/* If sufficient main memory allows the frame to be directly allocated,
we must update the frame table with a new entry, and grow lru_list. */
/* If sufficient main memory allows the frame to be directly allocated,
we must update the frame table with a new entry, and grow lru_list. */
else
{
/* Must own lru_lock here, as otherwise there is a race condition
with next_victim either being NULL or uninitialized. */
frame_metadata = malloc (sizeof (struct frame_entry));
frame_metadata->frame = frame;
/* Newly allocated frames are pushed to the back of the circular queue
represented by lru_list. Must explicitly handle the case where the
circular queue is empty (when next_victim == NULL). */
if (next_victim == NULL)
{
/* Must own lru_lock here, as otherwise there is a race condition
with next_victim either being NULL or uninitialized. */
frame_metadata = malloc (sizeof (struct frame_metadata));
frame_metadata->frame = frame;
/* Newly allocated frames are pushed to the back of the circular queue
represented by lru_list. Must explicitly handle the case where the
circular queue is empty (when next_victim == NULL). */
if (next_victim == NULL)
{
list_push_back (&lru_list, &frame_metadata->list_elem);
next_victim = &frame_metadata->list_elem;
}
else
{
struct list_elem *lru_tail = lru_prev (next_victim);
list_insert (lru_tail, &frame_metadata->list_elem);
}
hash_insert (&frame_table, &frame_metadata->hash_elem);
list_push_back (&lru_list, &frame_metadata->list_elem);
next_victim = &frame_metadata->list_elem;
}
else
{
struct list_elem *lru_tail = lru_prev (next_victim);
list_insert (lru_tail, &frame_metadata->list_elem);
}
hash_insert (&frame_table, &frame_metadata->hash_elem);
}
frame_metadata->upage = upage;
frame_metadata->owner = owner;
frame_metadata->pinned = false;
lock_release (&lru_lock);
return frame_metadata->frame;
void *frame_addr = frame_metadata->frame;
lock_release (&frame_lock);
return frame_addr;
}
void
frame_pin (void *frame)
{
struct frame_metadata *frame_metadata = frame_metadata_get (frame);
struct frame_entry *frame_metadata = frame_get (frame);
if (frame_metadata == NULL)
PANIC ("Attempted to pin a frame at an unallocated kernel address '%p'\n",
frame);
@@ -166,7 +132,7 @@ frame_pin (void *frame)
void
frame_unpin (void *frame)
{
struct frame_metadata *frame_metadata = frame_metadata_get (frame);
struct frame_entry *frame_metadata = frame_get (frame);
if (frame_metadata == NULL)
PANIC ("Attempted to unpin a frame at an unallocated kernel address '%p'\n",
frame);
@@ -179,104 +145,111 @@ frame_unpin (void *frame)
memory & metadata struct. Panics if the frame isn't active in memory. */
void
frame_free (void *frame)
{
lock_acquire(&frame_lock);
struct frame_entry key_metadata;
key_metadata.frame = frame;
struct hash_elem *e =
hash_delete (&frame_table, &key_metadata.hash_elem);
if (e == NULL)
return;
struct frame_entry *frame_metadata =
hash_entry (e, struct frame_entry, hash_elem);
struct page_entry *page = page_get (frame_metadata->upage);
if (page != NULL)
{
struct frame_metadata key_metadata;
key_metadata.frame = frame;
struct hash_elem *e =
hash_delete (&frame_table, &key_metadata.hash_elem);
if (e == NULL) PANIC ("Attempted to free a frame at kernel address %p, "
"but this address is not allocated!\n", frame);
struct frame_metadata *frame_metadata =
hash_entry (e, struct frame_metadata, hash_elem);
lock_acquire (&lru_lock);
list_remove (&frame_metadata->list_elem);
/* If we're freeing the frame marked as the next victim, update
next_victim to either be the next least recently used page, or NULL
if no pages are loaded in main memory. */
if (&frame_metadata->list_elem == next_victim)
{
if (list_empty (&lru_list))
next_victim = NULL;
else
next_victim = lru_next (next_victim);
}
lock_release (&lru_lock);
free (frame_metadata);
palloc_free_page (frame);
page->frame = NULL;
}
list_remove (&frame_metadata->list_elem);
/* If we're freeing the frame marked as the next victim, update
next_victim to either be the next least recently used page, or NULL
if no pages are loaded in main memory. */
if (&frame_metadata->list_elem == next_victim)
{
if (list_empty (&lru_list))
next_victim = NULL;
else
next_victim = lru_next (next_victim);
}
free (frame_metadata);
palloc_free_page (frame);
lock_release (&frame_lock);
}
/* TODO: Account for page aliases when checking accessed bit. */
/* A pre-condition for calling this function is that the calling thread
owns lru_lock and that lru_list is non-empty. */
static struct frame_metadata *
static struct frame_entry *
get_victim (void)
{
struct list_elem *e = next_victim;
struct frame_entry *frame_metadata;
uint32_t *pd;
void *upage;
for (;;)
{
struct list_elem *e = next_victim;
struct frame_metadata *frame_metadata;
uint32_t *pd;
void *upage;
for (;;)
{
frame_metadata = list_entry (e, struct frame_metadata, list_elem);
pd = frame_metadata->owner->pagedir;
upage = frame_metadata->upage;
e = lru_next (e);
frame_metadata = list_entry (e, struct frame_entry, list_elem);
pd = frame_metadata->owner->pagedir;
upage = frame_metadata->upage;
e = lru_next (e);
/* Skip pinned frames */
if (frame_metadata->pinned)
continue;
/* Skip pinned frames */
if (frame_metadata->pinned)
continue;
if (!pagedir_is_accessed (pd, upage))
break;
if (!pagedir_is_accessed (pd, upage))
break;
pagedir_set_accessed (pd, upage, false);
}
next_victim = e;
return frame_metadata;
pagedir_set_accessed (pd, upage, false);
}
next_victim = e;
return frame_metadata;
}
/* Hash function for frame metadata, used for storing entries in the
frame table. */
unsigned
frame_metadata_hash (const struct hash_elem *e, void *aux UNUSED)
{
struct frame_metadata *frame_metadata =
hash_entry (e, struct frame_metadata, hash_elem);
frame_hash (const struct hash_elem *e, void *aux UNUSED)
{
struct frame_entry *entry =
hash_entry (e, struct frame_entry, hash_elem);
return hash_bytes (&frame_metadata->frame, sizeof (frame_metadata->frame));
}
return hash_bytes (&entry->frame, sizeof (entry->frame));
}
/* 'less_func' comparison function for frame metadata, used for comparing
/* 'less_func' comparison function for frame metadata, used for comparing
the keys of the frame table. Returns true iff the kernel virtual address
of the first frame is less than that of the second frame. */
bool
frame_metadata_less (const struct hash_elem *a_, const struct hash_elem *b_,
void *aux UNUSED)
frame_less (const struct hash_elem *a_, const struct hash_elem *b_,
void *aux UNUSED)
{
struct frame_metadata *a =
hash_entry (a_, struct frame_metadata, hash_elem);
struct frame_metadata *b =
hash_entry (b_, struct frame_metadata, hash_elem);
struct frame_entry *a =
hash_entry (a_, struct frame_entry, hash_elem);
struct frame_entry *b =
hash_entry (b_, struct frame_entry, hash_elem);
return a->frame < b->frame;
}
static struct frame_metadata *
frame_metadata_get (void *frame)
static struct frame_entry *
frame_get (void *frame)
{
struct frame_metadata key_metadata;
key_metadata.frame = frame;
struct frame_entry fake_frame;
fake_frame.frame = frame;
struct hash_elem *e = hash_find (&frame_table, &key_metadata.hash_elem);
struct hash_elem *e = hash_find (&frame_table, &fake_frame.hash_elem);
if (e == NULL) return NULL;
return hash_entry (e, struct frame_metadata, hash_elem);
return hash_entry (e, struct frame_entry, hash_elem);
}
/* Returns the next recently used element after the one provided, which

12
src/vm/page.c
View File

@@ -42,9 +42,10 @@ page_insert (struct file *file, off_t ofs, void *upage, uint32_t read_bytes,
if (page == NULL)
return NULL;
page->upage = upage;
page->frame = NULL;
page->file = file;
page->offset = ofs;
page->upage = upage;
page->read_bytes = read_bytes;
page->zero_bytes = zero_bytes;
page->writable = writable;
@@ -102,6 +103,8 @@ page_load (struct page_entry *page, bool writable)
/* Zero out the remaining bytes in the frame. */
memset (frame + page->read_bytes, 0, page->zero_bytes);
page->frame = frame;
/* Mark the page as loaded successfully. */
return true;
}
@@ -111,7 +114,12 @@ page_load (struct page_entry *page, bool writable)
void
page_cleanup (struct hash_elem *e, void *aux UNUSED)
{
free (hash_entry (e, struct page_entry, elem));
struct page_entry *page = hash_entry (e, struct page_entry, elem);
if (page->frame != NULL)
frame_free (page->frame);
free (page);
}
/* Updates the 'owner' thread's page table entry for virtual address 'upage'

1
src/vm/page.h
View File

@@ -12,6 +12,7 @@ enum page_type {
struct page_entry {
enum page_type type; /* Type of Data that should go into the page */
void *upage; /* Start Address of the User Page (Key of hash table). */
void *frame; /* Frame Address where the page is loaded. */
/* File Data */
struct file *file; /* Pointer to the file for executables. */