feat: incorporate lazy-loading data & helpers into supplemental page table

src/threads/thread.h

@@ -143,6 +143,10 @@ struct thread
     struct hash open_files;             /* Hash Table of FD -> Struct File. */
 #endif
 
+#ifdef VM
+  struct hash pages;                    /* Table of open user pages. */
+#endif
+
     void *curr_esp;
 
     /* Owned by thread.c. */

src/userprog/process.c

@@ -118,7 +118,6 @@ process_execute (const char *cmd)
 
 static void *get_usr_kpage (enum palloc_flags flags, void *upage);
 static void free_usr_kpage (void *kpage);
-static bool install_page (void *upage, void *kpage, bool writable);
 
 static bool process_init_stack (char *cmd_saveptr, void **esp, char *file_name);
 static void *push_to_stack (void **esp, void *data, size_t data_size);
@@ -809,7 +808,7 @@ free_usr_kpage (void *kpage)
    with palloc_get_page().
    Returns true on success, false if UPAGE is already mapped or
    if memory allocation fails. */
-static bool
+bool
 install_page (void *upage, void *kpage, bool writable)
 {
   struct thread *t = thread_current ();

src/userprog/process.h

@@ -8,4 +8,6 @@ int process_wait (tid_t);
 void process_exit (void);
 void process_activate (void);
 
+bool install_page (void *upage, void *kpage, bool writable);
+
 #endif /* userprog/process.h */

src/vm/page.c

@@ -1,10 +1,118 @@
 #include "page.h"
-#include "userprog/pagedir.h"
+#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);
+}
+
+/* Comparator function for the SPT table. Compares two entries based on their
+   upages. */
+bool
+page_less (const struct hash_elem *a_, const struct hash_elem *b_,
+           void *aux UNUSED)
+{
+  const struct page_entry *a = hash_entry (a_, struct page_entry, elem);
+  const struct page_entry *b = hash_entry (b_, struct page_entry, elem);
+
+  return a->upage < b->upage;
+}
+
+/* Allocate and insert a new page entry into the thread's page table. */
+struct page_entry *
+page_insert (struct file *file, off_t ofs, void *upage, uint32_t read_bytes,
+             uint32_t zero_bytes, bool writable, enum page_type type)
+{
+  struct page_entry *page = malloc(sizeof (struct page_entry));
+  if (page == NULL)
+    return NULL;
+
+  page->file = file;
+  page->offset = ofs;
+  page->upage = upage;
+  page->read_bytes = read_bytes;
+  page->zero_bytes = zero_bytes;
+  page->writable = writable;
+  page->type = type;
+
+  hash_insert (&thread_current ()->pages, &page->elem);
+  return page;
+}
+
+/* Gets a page_entry from the starting address of the page. Returns NULL if no
+   such page_entry exists in the hash map.*/
+struct page_entry *
+page_get (void *upage)
+{
+  struct page_entry fake_page_entry;
+  fake_page_entry.upage = upage;
+
+  struct hash_elem *e
+    = hash_find (&thread_current ()->pages, &fake_page_entry.elem);
+
+  if (e == NULL)
+      return NULL;
+
+  return hash_entry (e, struct page_entry, elem);
+}
+
+bool
+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 (0, page->upage, thread_current ());
+  if (frame == NULL)
+    PANIC ("Could not allocate a frame to load page into memory.");
+
+  /* Map the page to the frame. */
+  if (!install_page (page->upage, frame, writable))
+    {
+      frame_free (frame);
+      return false;
+    }
+
+  /* Move the file pointer to the correct location in the file. Then, read the
+     data from the file into the frame. Checks that we were able to read the
+     expected number of bytes. */
+  file_seek (page->file, page->offset);
+  if (file_read (page->file, frame, page->read_bytes) != (int) page->read_bytes)
+  {
+    frame_free (frame);
+    return false;
+  }
+
+  /* Zero out the remaining bytes in the frame. */
+  memset (frame + page->read_bytes, 0, page->zero_bytes);
+
+  /* Mark the page as loaded successfully. */
+  return true;
+}
+
+/* Function to clean up a page_entry. Given the elem of that page_entry, frees
+   the page_entry itself. */
+void
+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. */

src/vm/page.h

@@ -2,7 +2,36 @@
 #define VM_PAGE_H
 
 #include "threads/thread.h"
+#include "filesys/off_t.h"
 
+enum page_type {
+  PAGE_EXECUTABLE,
+  PAGE_EMPTY
+};
+
+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). */
+
+  /* File Data */
+  struct file *file;   /* Pointer to the file for executables. */
+  off_t offset;        /* Offset of the page content within the file. */
+  uint32_t read_bytes; /* Number of bytes to read within the page. */
+  uint32_t zero_bytes; /* Number of bytes to zero within the page. */
+  bool writable;       /* Flag for whether this page is writable or not. */
+
+  struct hash_elem elem; /* An elem for the hash table. */
+};
+
+unsigned page_hash (const struct hash_elem *e, void *aux);
+bool page_less (const struct hash_elem *a_, const struct hash_elem *b_,
+                void *aux);
+struct page_entry *page_insert (struct file *file, off_t ofs, void *upage,
+                                uint32_t read_bytes, uint32_t zero_bytes,
+                                bool writable, enum page_type type);
+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 *);