Move Preload() code to MappedFile

net/disk_cache/blockfile/mapped_file.cc

 // Copyright 2013 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 "net/disk_cache/blockfile/mapped_file.h"
 
+#include <algorithm>
+
+#include "base/memory/scoped_ptr.h"
+
 namespace disk_cache {
 
 // Note: Most of this class is implemented in platform-specific files.
 
 bool MappedFile::Load(const FileBlock* block) {
   size_t offset = block->offset() + view_size_;
   return Read(block->buffer(), block->size(), offset);
 }
 
 bool MappedFile::Store(const FileBlock* block) {
   size_t offset = block->offset() + view_size_;
   return Write(block->buffer(), block->size(), offset);
 }
 
 bool MappedFile::Load(const FileBlock* block,
                       FileIOCallback* callback,
                       bool* completed) {
   size_t offset = block->offset() + view_size_;
   return Read(block->buffer(), block->size(), offset, callback, completed);
 }
 
 bool MappedFile::Store(const FileBlock* block,
                        FileIOCallback* callback,
                        bool* completed) {
   size_t offset = block->offset() + view_size_;
   return Write(block->buffer(), block->size(), offset, callback, completed);
 }
 
+bool MappedFile::Preload() {
+  static const size_t kPreloadBufferSize = 16384;

[rvargas (doing something else), 2014/03/20 19:05:19]

The files have a limited size... the index is at most half a meg, and the mapped
section of other files is only two pages. Are you really concerned about
alloc/use/free of half a meg? I think it is much better for startup performance
to perform a single read than 32 disk reads.

+  size_t file_len = GetLength();
+  size_t left_to_read = file_len;
+  scoped_ptr<char[]> buf(new char[kPreloadBufferSize]);
+  while (left_to_read > 0) {
+    size_t to_read = std::min(kPreloadBufferSize, left_to_read);
+    size_t offset = file_len - left_to_read;
+    if (!Read(buf.get(), to_read, offset)) {
+      return false;
+    }
+    left_to_read -= to_read;
+  }
+  return true;
+}
 }  // namespace disk_cache