Scale backing store cache size

chrome/browser/renderer_host/backing_store.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/renderer_host/backing_store.h"
 
+#include "base/sys_info.h"
 #include "chrome/browser/renderer_host/render_widget_host.h"
+#include "chrome/common/chrome_constants.h"
 
 namespace {
 
 typedef OwningMRUCache<RenderWidgetHost*, BackingStore*> BackingStoreCache;
 static BackingStoreCache* cache = NULL;
 
 // Returns the size of the backing store cache.
-// TODO(iyengar) Make this dynamic, i.e. based on the available resources
-// on the machine.
 static int GetBackingStoreCacheSize() {
-  const int kMaxSize = 5;
-  return kMaxSize;
+  // This uses a similar approach to GetMaxRendererProcessCount.  The goal
+  // is to reduce memory pressure and swapping on low-resource machines.
+  static const int kMaxDibCountByRamTier[] = {
+    2,  // less than 256MB
+    3,  // 256MB
+    4,  // 512MB
+    5   // 768MB and above
+  };
+
+  static int max_size = kMaxDibCountByRamTier[
+          std::min(base::SysInfo::AmountOfPhysicalMemoryMB() / 256,
+                   static_cast<int>(arraysize(kMaxDibCountByRamTier)) - 1)];
+  return max_size;
 }
 
 // Creates the backing store for the host based on the dimensions passed in.
 // Removes the existing backing store if there is one.
 BackingStore* CreateBackingStore(RenderWidgetHost* host,
                                  const gfx::Size& backing_store_size) {
   BackingStoreManager::RemoveBackingStore(host);
 
   BackingStore* backing_store = host->AllocBackingStore(backing_store_size);
   int backing_store_cache_size = GetBackingStoreCacheSize();
@@ skipping 69 matching lines @@
   if (it == cache->end())
     return;
 
   cache->Erase(it);
 
   if (cache->empty()) {
     delete cache;
     cache = NULL;
   }
 }