lazy tlb shootdown: only shoot down when a subsequent map reuses virtual addrs

2cad69c2 · Nickolai Zeldovich · 570214f8 · 2cad69c2 · 2cad69c2 · 2cad69c2
--- a/include/proc.hh
+++ b/include/proc.hh
@@ -85,6 +85,7 @@ struct proc : public rcu_freed {
  LIST_ENTRY(proc) cv_waiters; // Linked list of processes waiting for oncv
  LIST_ENTRY(proc) cv_sleep;   // Linked list of processes sleeping on a cv
  u64 user_fs_;
+  u64 unmap_tlbreq_;

  static proc* alloc();
  void         set_state(procstate_t s);

--- a/kernel/proc.cc
+++ b/kernel/proc.cc
@@ -41,7 +41,7 @@ proc::proc(int npid) :
  pid(npid), parent(0), tf(0), context(0), killed(0),
  ftable(0), cwd(0), tsc(0), curcycles(0), cpuid(0), epoch(0),
  cpu_pin(0), runq(0), oncv(0), cv_wakeup(0),
-  user_fs_(0), state_(EMBRYO)
+  user_fs_(0), unmap_tlbreq_(0), state_(EMBRYO)
 {
  snprintf(lockname, sizeof(lockname), "cv:proc:%d", pid);
  initlock(&lock, lockname+3, LOCKSTAT_PROC);

--- a/kernel/vm.cc
+++ b/kernel/vm.cc
@@ -422,6 +422,8 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
      });
  if (needtlb && dotlb)
    tlbflush();
+  else
+    tlbflush(myproc()->unmap_tlbreq_);
  return 0;
 }

@@ -470,8 +472,12 @@ vmap::remove(uptr vma_start, uptr len)
        }
      }
    });
-  if (needtlb)
-    tlbflush();
+  if (needtlb) {
+    // eager tlb shootdown
+    //tlbflush();
+    // lazy tlb shootdown
+    myproc()->unmap_tlbreq_ = tlbflush_req++;
+  }
  return 0;
 }