1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // This file defines utility functions to pre-read a PE Image in order to 6 // avoid hard page faults when the image is subsequently loaded into memory 7 // for execution. 8 9 #ifndef CHROME_APP_IMAGE_PRE_READER_WIN_H_ 10 #define CHROME_APP_IMAGE_PRE_READER_WIN_H_ 11 12 #include "base/basictypes.h" 13 14 // This class defines static helper functions to pre-read a PE Image in order 15 // to avoid hard page faults when the image is subsequently loaded into memory 16 // for execution. 17 class ImagePreReader { 18 public: 19 // Reads the file passed in as a PE Image and touches pages to avoid 20 // subsequent hard page faults during LoadLibrary. The size to be pre-read 21 // is passed in. If it is 0 then the whole file is paged in. The step size 22 // which indicates the number of bytes to skip after every page touched is 23 // also passed in. 24 // 25 // This function checks the Windows version to determine which pre-reading 26 // mechanism to use. 27 static bool PreReadImage(const wchar_t* file_path, 28 size_t size_to_read, 29 size_t step_size); 30 31 // Loads the file passed in as PE Image and touches a percentage of the 32 // pages in each of the image's sections to avoid subsequent hard page 33 // faults during LoadLibrary. 34 // 35 // This function checks the Windows version to determine which pre-reading 36 // mechanism to use. 37 // 38 // The percentage of the file to be read is an integral value between 0 and 39 // 100, inclusive. If it is 0 then this is a NOP, if it is 100 (or greater) 40 // then the whole file is paged in sequentially via PreReadImage. Otherwise, 41 // for each section, in order, the given percentage of the blocks in that 42 // section are paged in, starting at the beginning of each section. For 43 // example: if percentage is 30 and there is a .text section and a .data 44 // section, then the first 30% of .text will be paged and the first 30% of 45 // .data will be paged in. 46 // 47 // The max_chunk_size indicates the number of bytes to read off the disk in 48 // each step (for Vista and greater, where this is the way the pages are 49 // warmed). 50 // 51 // This function is intended to be used in the context of a PE image with 52 // an optimized layout, such that the blocks in each section are arranged 53 // with the data and code most needed for startup moved to the front. 54 // See also: http://code.google.com/p/chromium/issues/detail?id=98508 55 static bool PartialPreReadImage(const wchar_t* file_path, 56 size_t percentage, 57 size_t max_chunk_size); 58 59 // Helper function used by PartialPreReadImage on Windows versions (Vista+) 60 // where reading through the file on disk serves to warm up the page cache. 61 // Exported for unit-testing purposes. 62 static bool PartialPreReadImageOnDisk(const wchar_t* file_path, 63 size_t percentage, 64 size_t max_chunk_size); 65 66 // Helper function used by PartialPreReadImage on Windows versions (XP) where 67 // cheaply loading the image then stepping through its address space serves 68 // to warm up the page cache. Exported for unit-testing purposes. 69 static bool PartialPreReadImageInMemory(const wchar_t* file_path, 70 size_t percentage); 71 }; // namespace internal 72 73 #endif // CHROME_APP_IMAGE_PRE_READER_WIN_H_ 74
