cowtest passed

kernel/kalloc.c

@@ -8,12 +8,23 @@
 #include "spinlock.h"
 #include "riscv.h"
 #include "defs.h"
-
 void freerange(void *pa_start, void *pa_end);
+uint64 getRefIdx(uint64 pa);
+
+struct spinlock reference_lock;  // 加锁
+int pm_reference[(PHYSTOP - KERNBASE)/PGSIZE];  // 记录物理页的引用计数
 
 extern char end[]; // first address after kernel.
                    // defined by kernel.ld.
 
+// va映射为idx
+uint64
+getRefIdx(uint64 pa)
+{
+  return (pa-KERNBASE)/PGSIZE;
+}
+
+
 struct run {
   struct run *next;
 };
@@ -27,6 +38,7 @@ void
 kinit()
 {
   initlock(&kmem.lock, "kmem");
+  initlock(&reference_lock, "pm_reference");
   freerange(end, (void*)PHYSTOP);
 }
 
@@ -51,15 +63,19 @@ kfree(void *pa)
   if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
     panic("kfree");
 
-  // Fill with junk to catch dangling refs.
-  memset(pa, 1, PGSIZE);
+  acquire(&reference_lock);
+  pm_reference[getRefIdx((uint64)pa)] --;
+  if(pm_reference[getRefIdx((uint64)pa)] <= 0){
+    // Fill with junk to catch dangling refs.
+    memset(pa, 1, PGSIZE);
+    r = (struct run*)pa;
+    acquire(&kmem.lock);
+    r->next = kmem.freelist;
+    kmem.freelist = r;
+    release(&kmem.lock);
+  }
 
-  r = (struct run*)pa;
-
-  acquire(&kmem.lock);
-  r->next = kmem.freelist;
-  kmem.freelist = r;
-  release(&kmem.lock);
+  release(&reference_lock);
 }
 
 // Allocate one 4096-byte page of physical memory.
@@ -76,7 +92,43 @@ kalloc(void)
     kmem.freelist = r->next;
   release(&kmem.lock);
 
-  if(r)
+  if(r){
     memset((char*)r, 5, PGSIZE); // fill with junk
+    pm_reference[getRefIdx((uint64) r)] = 1;
+  }
   return (void*)r;
 }
+
+// reference操作
+void
+reference_operation(void* pa, int op)
+{
+  acquire(&reference_lock);
+  if(op) pm_reference[getRefIdx((uint64)pa)]++;
+  else pm_reference[getRefIdx((uint64)pa)]--;
+  release(&reference_lock);
+}
+
+void*
+cowcopy_pa(void* pa){
+  acquire(&reference_lock);
+  if(pm_reference[getRefIdx((uint64)pa)] <= 1){
+    release(&reference_lock);
+    return pa;
+  }
+
+  char* new = kalloc();
+  if(new == 0){
+    release(&reference_lock);
+    panic("out of memory");
+    return 0;
+  }
+
+  memmove((void*)new, pa, PGSIZE);
+
+  // 变更引用计数
+  pm_reference[getRefIdx((uint64)pa)] --;
+  release(&reference_lock);
+  return (void*)new;
+}
+