Update frame: When evicting an mmapped file page, write it back to the file if it is dirty

src/vm/frame.c

@@ -2,12 +2,13 @@
 #include <hash.h>
 #include <list.h>
 #include <string.h>
-
 #include "frame.h"
 #include "page.h"
+#include "filesys/file.h"
 #include "threads/malloc.h"
 #include "threads/vaddr.h"
 #include "userprog/pagedir.h"
+#include "userprog/syscall.h"
 #include "threads/synch.h"
 
 /* Hash table that maps every active frame's kernel virtual address
@@ -91,9 +92,26 @@ frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
       struct frame_metadata *victim = get_victim ();
       ASSERT (victim != NULL); /* get_victim () should never return null. */
 
-      /* 2. Swap out victim into disk. */
+      /* 2. Handle victim page writing based on its type. */
+      struct page_entry *victim_page = page_get (victim->upage);
+      if (victim_page != NULL && victim_page->type == PAGE_MMAP)
+        {
+          /* If it was a memory-mapped file page, we just write it back
+             to the file if it was dirty. */
+          if (pagedir_is_dirty(owner->pagedir, victim->upage))
+            {
+              lock_acquire (&filesys_lock);
+              file_write_at (victim_page->file, victim->upage,
+                             victim_page->read_bytes, victim_page->offset);
+              lock_release (&filesys_lock);
+            }
+
+        }
+      else
+        /* Otherwise, insert the page into swap. */
         page_insert_swapped (victim->upage, victim->frame, victim->owner);
 
+
       /* If zero flag is set, zero out the victim page. */
       if (flags & PAL_ZERO)
         memset (victim->frame, 0, PGSIZE);