atomic vm refcounts

f1490815 · Nickolai Zeldovich · d61e3535 · f1490815 · f1490815 · f1490815
--- a/proc.cc
+++ b/proc.cc
@@ -582,7 +582,7 @@ fork(int flags)
    }
  } else {
    np->vmap = myproc()->vmap;
-    __sync_fetch_and_add(&np->vmap->ref, 1);
+    np->vmap->ref++;
  }

  np->brk = myproc()->brk;

--- a/vm.cc
+++ b/vm.cc
@@ -22,7 +22,7 @@ enum { vm_debug = 0 };
 static void
 vmn_decref(struct vmnode *n)
 {
-  if(subfetch(&n->ref, 1) == 0)
+  if(--n->ref == 0)
    vmn_free(n);
 }

@@ -84,7 +84,7 @@ vmn_allocpg(u64 npg)
 void
 vmap_decref(struct vmap *m)
 {
-  if(subfetch(&m->ref, 1) == 0)
+  if(--m->ref == 0)
    vmap_free(m);
 }

@@ -216,7 +216,7 @@ pagefault(struct vmap *vmap, uptr va, u32 err)

  if (vm_debug)
    cprintf("pagefault: err 0x%x va 0x%lx type %d ref %lu pid %d\n",
-            err, va, m->va_type, m->n->ref, myproc()->pid);
+            err, va, m->va_type, (u64) m->n->ref, myproc()->pid);

  if (m->va_type == COW && (err & FEC_WR)) {
    if (pagefault_wcow(vmap, va, pte, m, npg) < 0) {
@@ -379,7 +379,7 @@ vmap_insert(struct vmap *m, struct vmnode *n, uptr va_start)
  e->va_start = va_start;
  e->va_end = va_start + len;
  e->n = n;
-  __sync_fetch_and_add(&n->ref, 1);
+  n->ref++;
  crange_add(m->cr, e->va_start, len, (void *) e);
  release(&m->lock);
  return 0;
@@ -410,7 +410,7 @@ vmap_copy_vma(struct range *r, void *_st)
  if(c->n == 0) {
    return 0;
  }
-  __sync_fetch_and_add(&c->n->ref, 1);
+  c->n->ref++;
  crange_add(st->cr, c->va_start, c->va_end - c->va_start, (void *) c);
  return 1;
 }

--- a/vm.hh
+++ b/vm.hh
 #define TREE

 #include "gc.hh"
+#include "atomic.hh"

 // A mapping of a chunk of an address space to
 // a specific memory object.
@@ -27,7 +28,7 @@ struct vma : public rcu_freed {
 struct vmnode {
  u64 npages;
  char *page[128];
-  u64 ref;
+  atomic<u64> ref;
  enum vmntype type;
  struct inode *ip;
  u64 offset;
@@ -44,7 +45,7 @@ struct vmap {
  struct vma* e[16];
 #endif
  struct spinlock lock;        // serialize map/lookup/unmap
-  u64 ref;
+  atomic<u64> ref;
  u64 alloc;
  pml4e_t *pml4;               // Page table
  char *kshared;