[wasm] Add histogram for code space per module

In the context of launching Liftoff, this will help us estimate the code
size increase and find a good value for the maximum allowed code space.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Ie76172edbf136629636911fe97c7ecdc940be86d
Reviewed-on: https://chromium-review.googlesource.com/1061497
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53220}

src/counters.h

@@ -1146,7 +1146,9 @@ class RuntimeCallTimerScope {
   HR(compile_script_cache_behaviour, V8.CompileScript.CacheBehaviour, 0, 19,   \
      20)                                                                       \
   HR(wasm_memory_allocation_result, V8.WasmMemoryAllocationResult, 0, 3, 4)    \
-  HR(wasm_address_space_usage_mb, V8.WasmAddressSpaceUsageMiB, 0, 1 << 20, 128)
+  HR(wasm_address_space_usage_mb, V8.WasmAddressSpaceUsageMiB, 0, 1 << 20,     \
+     128)                                                                      \
+  HR(wasm_module_code_size_mb, V8.WasmModuleCodeSizeMiB, 0, 256, 64)
 
 #define HISTOGRAM_TIMER_LIST(HT)                                               \
   /* Garbage collection timers. */                                             \

src/isolate.cc

@@ -3012,6 +3012,8 @@ bool Isolate::Init(StartupDeserializer* des) {
       counters()->wasm_memory_allocation_result());
   wasm_engine_->memory_tracker()->SetAddressSpaceUsageHistogram(
       counters()->wasm_address_space_usage_mb());
+  wasm_engine_->code_manager()->SetModuleCodeSizeHistogram(
+      counters()->wasm_module_code_size_mb());
 
 // Initialize the interface descriptors ahead of time.
 #define INTERFACE_DESCRIPTOR(Name, ...) \

src/wasm/wasm-code-manager.cc

@@ -985,14 +985,19 @@ void WasmCodeManager::FreeNativeModule(NativeModule* native_module) {
   }
   native_module->owned_code_space_.clear();
 
+  size_t code_size = native_module->committed_code_space_;
+  DCHECK(IsAligned(code_size, AllocatePageSize()));
+
+  if (module_code_size_mb_) {
+    module_code_size_mb_->AddSample(static_cast<int>(code_size / MB));
+  }
+
   // No need to tell the GC anything if we're destroying the heap,
   // which we currently indicate by having the isolate_ as null
   if (isolate_ == nullptr) return;
-  size_t freed_code_space = native_module->committed_code_space_;
-  DCHECK(IsAligned(freed_code_space, AllocatePageSize()));
-  remaining_uncommitted_code_space_.fetch_add(freed_code_space);
+  remaining_uncommitted_code_space_.fetch_add(code_size);
   isolate_->AdjustAmountOfExternalAllocatedMemory(
-      -static_cast<int64_t>(freed_code_space));
+      -static_cast<int64_t>(code_size));
 }
 
 // TODO(wasm): We can make this more efficient if needed. For

src/wasm/wasm-code-manager.h

@@ -22,6 +22,7 @@ namespace internal {
 
 struct CodeDesc;
 class Code;
+class Histogram;
 class WasmCompiledModule;
 
 namespace wasm {
@@ -388,6 +389,10 @@ class V8_EXPORT_PRIVATE WasmCodeManager final {
   WasmCode* GetCodeFromStartAddress(Address pc) const;
   size_t remaining_uncommitted_code_space() const;
 
+  void SetModuleCodeSizeHistogram(Histogram* histogram) {
+    module_code_size_mb_ = histogram;
+  }
+
  private:
   friend class NativeModule;
 
@@ -412,6 +417,9 @@ class V8_EXPORT_PRIVATE WasmCodeManager final {
   // TODO(mtrofin): remove the dependency on isolate.
   v8::Isolate* isolate_;
 
+  // Histogram to update with the maximum used code space for each NativeModule.
+  Histogram* module_code_size_mb_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(WasmCodeManager);
 };