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Merge remote-tracking branch 'origin/vm/page-swap-synch' into vm/virtual-memory/saleh

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# Conflicts:
#	.gitlab-ci.yml
#	src/Makefile.build
#	src/threads/thread.c
#	src/userprog/exception.c
#	src/userprog/process.c
#	src/vm/frame.c
#	src/vm/page.c
#	src/vm/page.h
#	src/vm/stackgrowth.c
#	src/vm/stackgrowth.h
This commit is contained in:
sBubshait
2024-12-05 02:21:53 +00:00
parent 1a8eb1bbe5 ac31fb1e1e
commit f13fd435cd
11 changed files with 222 additions and 58 deletions
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181
src/vm/frame.c
View File

@@ -7,6 +7,7 @@
#include "page.h"
#include "threads/malloc.h"
#include "threads/vaddr.h"
#include "userprog/pagedir.h"
#include "threads/synch.h"
#include "devices/swap.h"
@@ -14,20 +15,22 @@
to its corresponding 'frame_metadata'.*/
struct hash frame_table;
/* Linked list of frame_metadata whose pages are predicted to currently
be in the working set of a process. They are not considered for
eviction, but are considered for demotion to the 'inactive' list. */
struct list active_list;
/* 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 list lru_list;
/* Linked list of frame_metadata whose pages are predicted to leave the
working set of their processes soon, so are considered for eviction.
Pages are considered for eviction from the tail end, and are initially
demoted to 'inactive' at the head. */
struct list inactive_list;
/* 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 the 'inactive' list. */
struct lock inactive_lock;
/* Protects access to 'lru_list'. */
struct lock lru_lock;
struct frame_metadata
{
@@ -45,22 +48,24 @@ struct frame_metadata
hash_hash_func frame_metadata_hash;
hash_less_func frame_metadata_less;
static struct list_elem *lru_next (struct list_elem *e);
static struct list_elem *lru_prev (struct list_elem *e);
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
the active & inactive lists. Also initializes the system's synchronisation
primitives. */
'lru_list' and its associated synchronisation primitives. */
void
frame_init (void)
{
hash_init (&frame_table, frame_metadata_hash, frame_metadata_less, NULL);
list_init (&active_list);
list_init (&inactive_list);
lock_init (&inactive_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
@@ -69,7 +74,10 @@ frame_init (void)
void *
frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
{
struct frame_metadata *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,
@@ -77,11 +85,20 @@ frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
into disk. */
if (frame == NULL)
{
/* TODO: Deal with race condition wherein a page may be evicted in one
thread while it's in the middle of being evicted in another. */
/* 1. Obtain victim. */
if (next_victim == NULL)
PANIC ("Couldn't allocate a single page to main memory!\n");
struct frame_metadata *victim = get_victim ();
if (victim == NULL)
return NULL;
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);
// 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);
@@ -90,30 +107,50 @@ frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
if (flags & PAL_ZERO)
memset (victim->frame, 0, PGSIZE);
frame = victim->frame;
/* 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. */
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_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);
}
struct frame_metadata *frame_metadata =
malloc (sizeof (struct frame_metadata));
frame_metadata->frame = frame;
frame_metadata->upage = upage;
frame_metadata->owner = owner;
lock_release (&lru_lock);
/* Newly faulted pages begin at the head of the inactive list. */
lock_acquire (&inactive_lock);
list_push_front (&inactive_list, &frame_metadata->list_elem);
lock_release (&inactive_lock);
/* Finally, insert frame metadata within the frame table, with the key as its
allocated kernel address. */
hash_replace (&frame_table, &frame_metadata->hash_elem);
return frame;
return frame_metadata->frame;
}
/* Attempt to deallocate a frame for a user process by removing it from the
frame table as well as active/inactive list, and freeing the underlying
page memory. Panics if the frame isn't active in memory. */
frame table as well as lru_list, and freeing the underlying page
memory & metadata struct. Panics if the frame isn't active in memory. */
void
frame_free (void *frame)
{
@@ -122,33 +159,56 @@ frame_free (void *frame)
struct hash_elem *e =
hash_delete (&frame_table, &key_metadata.hash_elem);
if (e == NULL) PANIC ("Attempted to free a frame without a corresponding "
"kernel address!\n");
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);
}
/* Obtain a pointer to the metadata of the frame we should evict next. */
/* 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 *
get_victim (void)
{
lock_acquire (&inactive_lock);
if (list_empty (&inactive_list))
struct list_elem *e = next_victim;
struct frame_metadata *frame_metadata;
uint32_t *pd;
void *upage;
for (;;)
{
return NULL;
}
else
{
struct list_elem *victim_elem = list_pop_back (&inactive_list);
lock_release (&inactive_lock);
return list_entry (victim_elem, struct frame_metadata, list_elem);
frame_metadata = list_entry (e, struct frame_metadata, list_elem);
pd = frame_metadata->owner->pagedir;
upage = frame_metadata->upage;
e = lru_next (e);
if (!pagedir_is_accessed (pd, upage))
break;
pagedir_set_accessed (pd, upage, false);
}
next_victim = e;
return frame_metadata;
}
/* Hash function for frame metadata, used for storing entries in the
@@ -177,3 +237,26 @@ frame_metadata_less (const struct hash_elem *a_, const struct hash_elem *b_,
return a->frame < b->frame;
}
/* Returns the next recently used element after the one provided, which
is achieved by iterating through lru_list like a circular queue
(wrapping around the list at the tail). */
static struct list_elem *
lru_next (struct list_elem *e)
{
if (!list_empty (&lru_list) && e == list_back (&lru_list))
return list_front (&lru_list);
return list_next (e);
}
/* Returns the previous recently used element after the one provided, which
is achieved by iterating through lru_list like a circular queue
(wrapping around the list at the head). */
static struct list_elem *
lru_prev (struct list_elem *e)
{
if (!list_empty (&lru_list) && e == list_front (&lru_list))
return list_back (&lru_list);
return list_prev (e);
}

53
src/vm/page.c
View File

@@ -2,18 +2,23 @@
#include <string.h>
#include <stdio.h>
#include "filesys/file.h"
#include "threads/pte.h"
#include "threads/malloc.h"
#include "threads/palloc.h"
#include "userprog/process.h"
#include "userprog/pagedir.h"
#include "vm/frame.h"
#define SWAP_FLAG_BIT 9
#define ADDR_START_BIT 12
/* Hashing function needed for the SPT table. Returns a hash for an entry,
based on its upage. */
unsigned
page_hash (const struct hash_elem *e, UNUSED void *aux)
{
struct page_entry *page = hash_entry (e, struct page_entry, elem);
return hash_ptr(page->upage);
return hash_ptr (page->upage);
}
/* Comparator function for the SPT table. Compares two entries based on their
@@ -71,7 +76,9 @@ page_load (struct page_entry *page, bool writable)
/* Allocate a frame for the page. If a frame allocation fails, then
frame_alloc should try to evict a page. If it is still NULL, the OS
panics as this should not happen if eviction is working correctly. */
void *frame = frame_alloc (PAL_USER, page->upage, thread_current ());
struct thread *t = thread_current ();
void *frame = frame_alloc (PAL_USER, page->upage, t);
pagedir_set_accessed (t->pagedir, page->upage, true);
if (frame == NULL)
PANIC ("Could not allocate a frame to load page into memory.");
@@ -106,3 +113,45 @@ page_cleanup (struct hash_elem *e, void *aux UNUSED)
{
free (hash_entry (e, struct page_entry, elem));
}
/* Updates the 'owner' thread's page table entry for virtual address 'upage'
to flag the page as being stored in swap, and stores the specified swap slot
value in the entry at the address bits for later retrieval from disk. */
void
page_set_swap (struct thread *owner, void *upage, size_t swap_slot)
{
uint32_t *pte = lookup_page (owner->pagedir, upage, false);
/* Store the provided swap slot in the address bits of the page table
entry, truncating excess bits. */
*pte |= (1 << SWAP_FLAG_BIT);
uint32_t swap_slot_bits = (swap_slot << ADDR_START_BIT) & PTE_ADDR;
*pte = (*pte & PTE_FLAGS) | swap_slot_bits;
invalidate_pagedir (owner->pagedir);
}
/* Returns true iff the page with user address 'upage' owned by 'owner'
is flagged to be in the swap disk via the owner's page table. */
bool
page_in_swap (struct thread *owner, void *upage)
{
uint32_t *pte = lookup_page (owner->pagedir, upage, false);
return pte != NULL &&
(*pte & (1 << SWAP_FLAG_BIT)) != 0;
}
/* Given that the page with user address 'upage' owned by 'owner' is flagged
to be in the swap disk via the owner's page table, returns its stored
swap slot. Otherwise panics the kernel. */
size_t
page_get_swap (struct thread *owner, void *upage)
{
uint32_t *pte = lookup_page (owner->pagedir, upage, false);
ASSERT (pte != NULL);
ASSERT ((*pte & PTE_P) == 0);
/* Masks the address bits and returns truncated value. */
return ((*pte & PTE_ADDR) >> ADDR_START_BIT);
}

2
src/vm/page.h
View File

@@ -32,7 +32,9 @@ struct page_entry *page_insert (struct file *file, off_t ofs, void *upage,
struct page_entry *page_get (void *upage);
bool page_load (struct page_entry *page, bool writable);
void page_cleanup (struct hash_elem *e, void *aux);
void page_set_swap (struct thread *, void *, size_t);
bool page_in_swap (struct thread *, void *);
size_t page_get_swap (struct thread *, void *);
#endif /* vm/frame.h */