--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/source/kalloc.c	Sun Oct 22 18:25:39 2017 +0900
@@ -0,0 +1,94 @@
+#include "types.h"
+#include "defs.h"
+#include "param.h"
+#include "memlayout.h"
+#include "mmu.h"
+#include "spinlock.h"
+
+void freerange(void *vstart, void *vend);
+extern char end[]; // first address after kernel loaded from ELF file
+
+struct run {
+  struct run *next;
+};
+
+struct {
+  struct spinlock lock;
+  int use_lock;
+  struct run *freelist;
+} kmem;
+
+// Initialization happens in two phases.
+// 1. main() calls kinit1() while still using entrypgdir to place just
+// the pages mapped by entrypgdir on free list.
+// 2. main() calls kinit2() with the rest of the physical pages
+// after installing a full page table that maps them on all cores.
+void
+kinit1(void *vstart, void *vend)
+{
+  initlock(&kmem.lock, "kmem");
+  kmem.use_lock = 0;
+  kmem.freelist = 0;
+  freerange(vstart, vend);
+}
+
+void
+kinit2(void *vstart, void *vend)
+{
+  freerange(vstart, vend);
+  kmem.use_lock = 1;
+}
+
+void
+freerange(void *vstart, void *vend)
+{
+  char *p;
+  p = (char*)PGROUNDUP((uint)vstart);
+  for(; p + PGSIZE <= (char*)vend; p += PGSIZE)
+    kfree(p);
+}
+
+//PAGEBREAK: 21
+// Free the page of physical memory pointed at by v,
+// which normally should have been returned by a
+// call to kalloc().  (The exception is when
+// initializing the allocator; see kinit above.)
+void
+kfree(char *v)
+{
+  struct run *r;
+
+  if((uint)v % PGSIZE || v < end || v2p(v) >= PHYSTOP)
+    panic("kfree");
+
+  // Fill with junk to catch dangling refs.
+  memset(v, 1, PGSIZE);
+
+  if(kmem.use_lock)
+    acquire(&kmem.lock);
+  r = (struct run*)v;
+  r->next = kmem.freelist;
+  kmem.freelist = r;
+  if(kmem.use_lock)
+    release(&kmem.lock);
+}
+
+// Allocate one 4096-byte page of physical memory.
+// Returns a pointer that the kernel can use.
+// Returns 0 if the memory cannot be allocated.
+char*
+kalloc(void)
+{
+  struct run *r;
+
+  if(kmem.use_lock)
+    acquire(&kmem.lock);
+  r = kmem.freelist;
+  if(r)
+    kmem.freelist = r->next;
+  if(kmem.use_lock)
+    release(&kmem.lock);
+  return (char*)r;
+}
+
+