過去十年中,作業系統的研究已不再侷限於monolithic kernel這種架構,而越來越多朝向microkernel的研究,那是由於: (1) Microkernel 這種微核心架構讓作業系統變得容易了解與學習,(2) 因核心內包含的東西少,讓作業系統較容易移植,且更有彈性,容易依照需求加減功能,(3) 扮演重要角色的訊息傳遞程式已不再過分的拖慢系統速度。
Minix 3 就是在過去十年中發展出來的一套微核心系統,一開始是教育性質,以教學為主,但目前也朝向嵌入式系統發展。在架構上它仍以僅支援IA-32為主,但目前已有相關研究是將它移植到其他架構上[4, 8]。這篇論文主要在探討其記憶體管理,將原來只有segmentation方式的管理變成能夠支援虛擬記憶體—也就是paging。
因此此論文分成兩個部分:第一部分將先實作出一個獨立管理記憶體的程式—pg,在Minix 3 這種接下kernel工作的程式稱做server ; 管理記憶體對於monolithic kernel來說是必須在kernel內完成的。第二部分將依IA-32的硬體支援去實作segmentation with paging的記憶體管理模型。

Over the past decade, researches on operating systems have been shifted from monolithic kernels towards microkernels for several reasons. Of them are: (1) It is easier to understand and debug because the kernel is much smaller. (2) It is much more secure and flexible because the kernel is small, and most of the kernel functions can be implemented as servers running in the user space instead of in the kernel space. (3) The message passing technique that is in the core of the microkernel has been improved, and thus the overhead required for the message passing has been highly reduced.
Minix 3 is one of the microkernels developed over the past decade and is aimed for educational purpose and small PCs. It is implemented on the IA-32 architecture and is based on the segmented memory model of IA-32. The purpose of this thesis is to use Minix 3 as a case study and to convert the segmented memory model adopted by the current implementation to coexisted with the demand paged memory model, which is also supported by the IA-32 architecture. That said, the thesis can be divided into two parts: The first part is to implement a new server called pager, which would take over the memory management subsystem of the Minix 3 microkernel and be used to offload the overhead of the kernel. The second part is to implement a virtual memory management subsystem that uses the segmentation with paging memory model of the IA-32 architecture.

Chapter 1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Development Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.3 Debugging Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Introduction to Minix 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.1 The Original Design of Minix . . . . . . . . . . . . . . . . . . . . . 4
1.3.2 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.3 System Call vs. Kernel Call . . . . . . . . . . . . . . . . . . . . . . 7
1.3.4 Memory Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Introduction to IA-32 Architecture . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.2 Protected-Mode Memory Management . . . . . . . . . . . . . . . . 12
1.4.3 Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4.4 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4.5 Interrupt and Exception Handling . . . . . . . . . . . . . . . . . . . 19
Chapter 2 Implementation: Part One 21
2.1 A Standalone Memory Management Server: Pager . . . . . . . . . . . . . . 21
2.1.1 Modifying the Kernel and Booting Structures . . . . . . . . . . . . . 22
2.1.2 Building the Memory Management Server . . . . . . . . . . . . . . . 23
2.1.3 Ignoring the SIGTERM Signal . . . . . . . . . . . . . . . . . . . . . . 24
Chapter 3 Comparing the Implementations 26
3.1 Two Different Approaches for Page Allocation . . . . . . . . . . . . . . . . 26
3.2 Where Should the Page-Directory and Page-Table be? . . . . . . . . . . . . . 28
3.2.1 When User Process Making a System Call? . . . . . . . . . . . . . . 28
3.2.2 EIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.3 Paying Special Attention to Memory Copy Functions . . . . . . . . . 32
3.2.4 Who Is in Charge of the Memory? . . . . . . . . . . . . . . . . . . . 32
3.3 Virtual Memory Layout for Minix 3 . . . . . . . . . . . . . . . . . . . . . . 33
Chapter 4 Implementation: Part Two 35
4.1 Rethinking the Role of Memory Management Server . . . . . . . . . . . . . 35
4.2 Initializing the Page Directory and Page Table in Minix . . . . . . . . . . . . 42
4.3 A Primitive Virtual Memory System . . . . . . . . . . . . . . . . . . . . . . 44
4.3.1 How It Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.3.2 Filling up Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.3.3 Linear Address Copy . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4 Page Fault and Dynamic Memory Allocation . . . . . . . . . . . . . . . . . 45
Chapter 5 Performance Evaluation 47
5.1 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Chapter 6 Related work 50
Chapter 7 Conclusion and Future Works 52
7.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
7.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Appendix A Serial Port Driver 57
Appendix B Source Code of Benchmarks 59
B.1 Fork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
B.2 Exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
B.3 Matrix Multiplication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Appendix C Source Code of Pager 62
C.1 alloc.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
C.2 const.h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
C.3 do alloc.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
C.4 do exec.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
C.5 do fork.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
C.6 do free.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
C.7 do segcopy.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
C.8 free.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
C.9 glo.h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
C.10 linear copy.s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
C.11 linear memzero.s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
C.12 main.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
C.13 memcopy.s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
C.14 memzero.s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
C.15 misc.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
C.16 pager.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
C.17 pg.h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
C.18 proto.h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
C.19 segcopy.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
C.20 table.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
C.21 type.h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

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