only do tlbflush if we zeroed some tlb entries

958c2e7f · Nickolai Zeldovich · 59bc213f · 958c2e7f
--- a/kernel/vm.cc
+++ b/kernel/vm.cc
@@ -300,16 +300,19 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
    span.replace(e);
  }
-  updatepages(pml4, e->vma_start, e->vma_end, [](atomic<pme_t> *p) {
+  bool needtlb = false;
+  updatepages(pml4, e->vma_start, e->vma_end, [&needtlb](atomic<pme_t> *p) {
      for (;;) {
        pme_t v = p->load();
        if (v & PTE_LOCK)
          continue;
        if (cmpxch(p, v, (pme_t) 0))
          break;
+        if (v != 0)
+          needtlb = true;
      }
    });
-  if(dotlb)
+  if (needtlb && dotlb)
    tlbflush();
  return 0;
 }
@@ -335,16 +338,20 @@ vmap::remove(uptr vma_start, uptr len)
    span.replace(0);
  }
-  updatepages(pml4, vma_start, vma_start + len, [](atomic<pme_t> *p) {
+  bool needtlb = false;
+  updatepages(pml4, vma_start, vma_start + len, [&needtlb](atomic<pme_t> *p) {
      for (;;) {
        pme_t v = p->load();
        if (v & PTE_LOCK)
          continue;
        if (cmpxch(p, v, (pme_t) 0))
          break;
+        if (v != 0)
+          needtlb = true;
      }
    });
-  tlbflush();
+  if (needtlb)
+    tlbflush();
  return 0;
 }