3 files changed, 14 insertions, 10 deletions

diff --git a/userprog/process.c b/userprog/process.c
index 80e327d..bf1a706 100644
--- a/userprog/process.c
+++ b/userprog/process.c
@@ -129,6 +129,7 @@ start_process (void *aux)
   process->parent_tid = aux_data->parent_thread->tid;
   thread->process = process;
 
+  /* initialize page and mmap table */
   page_table_init (&thread->page_table);
   if (!mmap_table_init (&process->mmap_table))
     goto signal;
@@ -151,10 +152,9 @@ start_process (void *aux)
   /* If process startup failed, quit. */
   if (thread->process == NULL)  {
     if (process != NULL) {
+      /* close/free memory mapped files and page table */
       /* close/free memory mapped files */
       mmap_table_free (&process->mmap_table);
-
-      /* free page table */
       page_table_free (&thread->page_table);
 
       if (process->fd_table.fds != NULL)
@@ -240,8 +240,9 @@ process_exit (void)
     lock_release (&filesys_lock);
   }
 
-  /* close/free memory mapped files */
+  /* close/free memory mapped files and page table */
   mmap_table_free (&proc->mmap_table);
+  page_table_free (&thread->page_table);
 
   int fd;
   for (fd = 2; fd <= proc->fd_table.fd_max; fd++) {
@@ -265,9 +266,6 @@ process_exit (void)
     pagedir_destroy (pd);
   }
 
-  /* free page table */
-  page_table_free (&thread->page_table);
-
   /* Destroy the process structure if the parent is not alive
    * any more. Atomic test and set would be sufficient here.
    */
diff --git a/vm/mmap.c b/vm/mmap.c
index 0dc9190..8620513 100644
--- a/vm/mmap.c
+++ b/vm/mmap.c
@@ -1,11 +1,11 @@
 #include <string.h>
-#include "userprog/pagedir.h"
-#include "userprog/process.h"
 #include "filesys/file.h"
 #include "threads/thread.h"
 #include "threads/vaddr.h"
 #include "threads/malloc.h"
 #include "threads/palloc.h"
+#include "userprog/pagedir.h"
+#include "userprog/process.h"
 #include "vm/mmap.h"
 #include "vm/page.h"
 
@@ -128,8 +128,12 @@ mmap_table_remove (struct mmap_table *table, mapid_t mapid)
           process_unlock_filesys ();
         }
 
+      /* free page and page table entry */
       if (pte != NULL)
+      {
+        pagedir_clear_page (thread->pagedir, pte->upage);
         free (pte);
+      }
 
       ofs += PGSIZE;
     }
diff --git a/vm/page.c b/vm/page.c
index b40382f..b98c553 100644
--- a/vm/page.c
+++ b/vm/page.c
@@ -1,10 +1,11 @@
 #include <string.h>
 #include "filesys/file.h"
-#include "userprog/process.h"
 #include "threads/thread.h"
 #include "threads/vaddr.h"
 #include "threads/malloc.h"
 #include "threads/palloc.h"
+#include "userprog/pagedir.h"
+#include "userprog/process.h"
 #include "vm/page.h"
 
 static unsigned page_table_hash (const struct hash_elem *e, void *aux UNUSED);
@@ -52,6 +53,7 @@ static void
 page_table_entry_free (struct hash_elem *e, void *aux UNUSED)
 {
   struct page_table_entry *pte = hash_entry (e, struct page_table_entry, elem);
+  pagedir_clear_page (thread_current ()->pagedir, pte->upage);
   free (pte);
 }
 
@@ -97,7 +99,7 @@ page_table_fetch (struct hash *ht, void *upage)
 }
 
 /* remove an entry from the page table. returns the element or NULL if not found.
-   the caller is responsible for freeing the element! */
+   the caller is responsible for freeing the element and the associated page! */
 struct page_table_entry *
 page_table_remove (struct hash *ht, void *upage)
 {