Add a ResourceConstraint for the embedder to specify that V8 is running on a...

Add a ResourceConstraint for the embedder to specify that V8 is running on a memory constrained device.

This enables us to specialize certain operations such that we limit memory
usage on low-memory devices, without reducing performance on devices which
are not memory constrained.

BUG=chromium:280984
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/23464022

Patch from Ross McIlroy <rmcilroy@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16608 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -3763,11 +3763,20 @@ class V8_EXPORT ResourceConstraints {
   uint32_t* stack_limit() const { return stack_limit_; }
   // Sets an address beyond which the VM's stack may not grow.
   void set_stack_limit(uint32_t* value) { stack_limit_ = value; }
+  Maybe<bool> is_memory_constrained() const { return is_memory_constrained_; }
+  // If set to true, V8 will limit it's memory usage, at the potential cost of
+  // lower performance.  Note, this option is a tentative addition to the API
+  // and may be removed or modified without warning.
+  void set_memory_constrained(bool value) {
+    is_memory_constrained_ = Maybe<bool>(value);
+  }
+
  private:
   int max_young_space_size_;
   int max_old_space_size_;
   int max_executable_size_;
   uint32_t* stack_limit_;
+  Maybe<bool> is_memory_constrained_;
 };
 
 

src/api.cc

@@ -624,7 +624,8 @@ ResourceConstraints::ResourceConstraints()
   : max_young_space_size_(0),
     max_old_space_size_(0),
     max_executable_size_(0),
-    stack_limit_(NULL) { }
+    stack_limit_(NULL),
+    is_memory_constrained_() { }
 
 
 bool SetResourceConstraints(ResourceConstraints* constraints) {
@@ -645,6 +646,10 @@ bool SetResourceConstraints(ResourceConstraints* constraints) {
     uintptr_t limit = reinterpret_cast<uintptr_t>(constraints->stack_limit());
     isolate->stack_guard()->SetStackLimit(limit);
   }
+  if (constraints->is_memory_constrained().has_value) {
+    isolate->set_is_memory_constrained(
+        constraints->is_memory_constrained().value);
+  }
   return true;
 }
 

src/isolate.h

@@ -1128,6 +1128,13 @@ class Isolate {
   // Given an address occupied by a live code object, return that object.
   Object* FindCodeObject(Address a);
 
+  bool is_memory_constrained() const {
+    return is_memory_constrained_;
+  }
+  void set_is_memory_constrained(bool value) {
+    is_memory_constrained_ = value;
+  }
+
  private:
   Isolate();
 
@@ -1299,6 +1306,7 @@ class Isolate {
   DateCache* date_cache_;
   unibrow::Mapping<unibrow::Ecma262Canonicalize> interp_canonicalize_mapping_;
   CodeStubInterfaceDescriptor* code_stub_interface_descriptors_;
+  bool is_memory_constrained_;
 
   // True if fatal error has been signaled for this isolate.
   bool has_fatal_error_;