Do not delay sweeping of pages that are completely free.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index a864c346740a8c05156ca809888f5a9959cb48a8..1fb5d5f438b152f23f6d1ea1ef53a8cd9cb3f26c 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -3623,14 +3623,6 @@ void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
       continue;
     }
 
-    if (lazy_sweeping_active) {
-      if (FLAG_gc_verbose) {
-        PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
-               reinterpret_cast<intptr_t>(p));
-      }
-      continue;
-    }
-
     // One unused page is kept, all further are released before sweeping them.
     if (p->LiveBytes() == 0) {
       if (unused_page_present) {
@@ -3644,6 +3636,14 @@ void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
       unused_page_present = true;
     }
 
+    if (lazy_sweeping_active) {
+      if (FLAG_gc_verbose) {
+        PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
+               reinterpret_cast<intptr_t>(p));
+      }
+      continue;
+    }
+
     switch (sweeper) {
       case CONSERVATIVE: {
         if (FLAG_gc_verbose) {