From 4ea6feac5fe663fe82de53632883ced6205f57f8 Mon Sep 17 00:00:00 2001
From: Andrew Waterman <waterman@cs.berkeley.edu>
Date: Sat, 14 Mar 2015 02:07:20 -0700
Subject: Check referenced/dirty bits

---
 v/vm.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/v/vm.c b/v/vm.c
index 10fc0cd..a085577 100644
--- a/v/vm.c
+++ b/v/vm.c
@@ -65,7 +65,13 @@ void evict(unsigned long addr)
   freelist_t* node = &user_mapping[addr/PGSIZE];
   if (node->addr)
   {
-    memcpy((void*)addr, (void*)node->addr, PGSIZE);
+    // check referenced and dirty bits
+    assert(l3pt[addr/PGSIZE] & PTE_R);
+    if (memcmp((void*)addr, (void*)node->addr, PGSIZE)) {
+      assert(l3pt[addr/PGSIZE] & PTE_D);
+      memcpy((void*)addr, (void*)node->addr, PGSIZE);
+    }
+
     user_mapping[addr/PGSIZE].addr = 0;
 
     if (freelist_tail == 0)
-- 
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