If a large object is truncated, also truncate the page.

runtime/vm/pages.cc

Index: runtime/vm/pages.cc
===================================================================
--- runtime/vm/pages.cc	(revision 37758)
+++ runtime/vm/pages.cc	(working copy)
@@ -182,6 +182,22 @@
 }
 
 
+void PageSpace::TruncateLargePage(HeapPage* page,
+                                  intptr_t new_object_size_in_bytes) {
+  const intptr_t old_object_size_in_bytes =
+      page->object_end() - page->object_start();
+  ASSERT(new_object_size_in_bytes < old_object_size_in_bytes);
+  const intptr_t new_page_size_in_words =
+      LargePageSizeInWordsFor(new_object_size_in_bytes);
+  VirtualMemory* memory = page->memory_;
+  const intptr_t old_page_size_in_words = (memory->size() >> kWordSizeLog2);
+  memory->Truncate(memory->start(), (new_page_size_in_words << kWordSizeLog2));
+  usage_.capacity_in_words -= old_page_size_in_words;
+  usage_.capacity_in_words += new_page_size_in_words;
+  page->set_object_end(page->object_start() + new_object_size_in_bytes);
+}
+
+
 void PageSpace::FreePage(HeapPage* page, HeapPage* previous_page) {
   usage_.capacity_in_words -= (page->memory_->size() >> kWordSizeLog2);
   // Remove the page from the list.
@@ -538,11 +554,14 @@
   page = large_pages_;
   while (page != NULL) {
     HeapPage* next_page = page->next();
-    bool page_in_use = sweeper.SweepLargePage(page);
-    if (page_in_use) {
+    const intptr_t bytes_to_end = sweeper.SweepLargePage(page);
+    if (bytes_to_end == 0) {
+      FreeLargePage(page, prev_page);
+    } else {
+      if (bytes_to_end < (page->object_end() - page->object_start())) {

[Ivan Posva, 2014/06/30 05:51:05]

I am wondering whether we want to move the logic here into TruncateLargePage by
checking whether the the old page size and new page size differ.

[koda, 2014/06/30 22:57:49]

Done.

+        TruncateLargePage(page, bytes_to_end);
+      }
       prev_page = page;
-    } else {
-      FreeLargePage(page, prev_page);
     }
     // Advance to the next page.
     page = next_page;