cc: Keep most recently used resources at the front of resource queue.

cc/resources/resource_pool.cc

 // Copyright 2012 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 "cc/resources/resource_pool.h"
 
 #include <algorithm>
 
 #include "base/format_macros.h"
 #include "base/strings/stringprintf.h"
@@ skipping 73 matching lines @@
 
   SetResourceUsageLimits(0, 0);
   DCHECK_EQ(0u, unused_resources_.size());
   DCHECK_EQ(0u, in_use_memory_usage_bytes_);
   DCHECK_EQ(0u, total_memory_usage_bytes_);
   DCHECK_EQ(0u, total_resource_count_);
 }
 
 Resource* ResourcePool::AcquireResource(const gfx::Size& size,
                                         ResourceFormat format) {
-  for (ResourceDeque::iterator it = unused_resources_.begin();
-       it != unused_resources_.end(); ++it) {
-    ScopedResource* resource = *it;
+  // Traverse the |unused_resources_| from rear end as MRU resources are
+  // held at the rear end of the queue. This touches LRU resources only if
+  // needed, which inreases possibility of expiring more LRU resources
+  // within kResourceExpirationDelayMs.
+  for (ResourceDeque::reverse_iterator rit = unused_resources_.rbegin();
+       rit != unused_resources_.rend(); ++rit) {
+    ScopedResource* resource = *rit;
     DCHECK(resource_provider_->CanLockForWrite(resource->id()));
 
     if (resource->format() != format)
       continue;
     if (resource->size() != size)
       continue;
 
+    // Get iterator from reverse_iterator pointing to the same resource.
+    ResourceDeque::iterator it =
+        static_cast<ResourceDeque::iterator>(--rit.base());

[reveman, 2015/11/02 06:07:51]

if we need this then can we add a base() function to ResourceDeque::iterator
instead of the static_cast?

[prashant.n, 2015/11/02 17:56:45]

IMO, iterators are different, so typecast would be good, to let user know what
is being done. Otherwise we need to modify scoped ptr deque.
WDYT?

     // Transfer resource to |in_use_resources_|.
     in_use_resources_.set(resource->id(), unused_resources_.take(it));
     in_use_memory_usage_bytes_ += ResourceUtil::UncheckedSizeInBytes<size_t>(
         resource->size(), resource->format());
     return resource;
   }
 
   scoped_ptr<PoolResource> pool_resource =
       PoolResource::Create(resource_provider_);
   GLenum target =
@@ skipping 182 matching lines @@
   for (const auto& resource : busy_resources_) {
     resource->OnMemoryDump(pmd, resource_provider_, false /* is_free */);
   }
   for (const auto& entry : in_use_resources_) {
     entry.second->OnMemoryDump(pmd, resource_provider_, false /* is_free */);
   }
   return true;
 }
 
 }  // namespace cc