Merge branch 'vm/lazy-loading' into vm/page-swap-synch

src/userprog/exception.c

@@ -5,13 +5,13 @@
 #include "userprog/gdt.h"
 #include "threads/interrupt.h"
 #include "threads/thread.h"
-#include "userprog/pagedir.h"
 #ifdef VM
 #include "vm/stackgrowth.h"
 #include "vm/frame.h"
 #include "vm/page.h"
 #include "devices/swap.h"
 #include "threads/vaddr.h"
+#include "userprog/pagedir.h"
 #endif
 
 /* Number of page faults processed. */
@@ -19,6 +19,7 @@ static long long page_fault_cnt;
 
 static void kill (struct intr_frame *);
 static void page_fault (struct intr_frame *);
+bool try_fetch_page (void *upage, bool write);
 
 /* Registers handlers for interrupts that can be caused by user
    programs.
@@ -156,6 +157,7 @@ page_fault (struct intr_frame *f)
 
 #ifdef VM
   struct thread *t = thread_current ();
+  void *upage = pg_round_down (fault_addr);
   if (user)
     {
       if (not_present)
@@ -167,7 +169,6 @@ page_fault (struct intr_frame *f)
           if (page_in_swap (t, fault_addr))
             {
               size_t swap_slot = page_get_swap (t, fault_addr);
-              void *upage = pg_round_down (fault_addr);
               void *kpage = frame_alloc (0, upage, t);
               swap_in (kpage, swap_slot);
 
@@ -192,6 +193,15 @@ page_fault (struct intr_frame *f)
       f->eax = 0xffffffff;
       return;
     }
+
+  /* If the fault address is in a user page that is not present, then it might
+  just need to be lazily loaded. So, we check our SPT to see if the page
+  is expected to have data loaded in memory. */
+  if (not_present && is_user_vaddr (upage) && upage != NULL)
+    {
+      if (try_fetch_page (upage, write))
+        return;
+    }
 #endif
 
   /* To implement virtual memory, delete the rest of the function
@@ -205,3 +215,32 @@ page_fault (struct intr_frame *f)
   kill (f);
 }
 
+bool
+try_fetch_page (void *upage, bool write)
+{
+  /* Check if the page is in the supplemental page table. That is, it is a page
+     that is expected to be in memory. */
+  struct page_entry *page = page_get (upage);
+  if (page == NULL)
+    return false;
+
+  /* An attempt to write to a non-writeable should fail. */
+  if (write && !page->writable)
+    return false;
+
+  /* Load the page into memory based on the type of data it is expecting. */
+  bool success = false;
+  switch (page->type) {
+    case PAGE_EXECUTABLE:
+      success = page_load (page, page->writable);
+      break;
+    default:
+      return false;
+  }
+
+  if (success && page->writable &&
+      !pagedir_is_writable(thread_current()->pagedir, upage))
+    pagedir_set_writable(thread_current()->pagedir, upage, true);
+
+  return success;
+}