![9© 2010-17 SysPlay Workshops <workshop@sysplay.in>
All Rights Reserved.
Memory (RAM)
Working of an MMU
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Valid Tag Frame Number
TLB (in Cache)
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Page Table (in RAM)
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Page Number [31:12] Offset [11:0] Virtual Address](https://image.slidesharecdn.com/linuxmemorymanagement-101003193751-phpapp01/85/Linux-Memory-Management-9-320.jpg)
![9© 2010-17 SysPlay Workshops <workshop@sysplay.in>
All Rights Reserved.
Memory (RAM)
Working of an MMU
1
1
0
1
Valid Tag Frame Number
TLB (in Cache)
1
Page Table (in RAM)
1
1
1
0
1
0
1
1
0
1
Page Number [31:12] Offset [11:0] Virtual Address](https://image.slidesharecdn.com/linuxmemorymanagement-101003193751-phpapp01/75/Linux-Memory-Management-9-2048.jpg)
Uploaded byAnil Kumar Pugalia
Linux Memory Management
Linux uses memory management to partition memory between kernel and application spaces, organize memory using virtual addresses, and swap memory between primary and secondary storage. It divides memory using paging into equal-sized pages, creates virtual address spaces, and uses an MMU to translate between virtual and physical addresses. This allows processes to run independently with their own logical view of memory while the physical memory is shared.
In this document
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Introduction to the SysPlay Workshops on Linux Memory Management.
Topics to be covered include memory management fundamentals, partitioning, organization, and swapping.
Memory management is crucial for multi-processing, program relocation, protection, sharing, and organizing execution.
Key tasks include memory division between OS and applications, involving relocation, protection, and sharing.
Explains segmentation (unequal sized) and paging (equal sized) with examples like malloc() and slab subsystem.
Discusses fragmentation types, space efficiency, and time efficiency for segmentation and paging.
Virtualization helps organize memory into physical and virtual addresses, using paging and segmentation.
Support for hardware and software MMUs in Linux kernels, and the use of uClinux for non-MMU processors.
Details working of an MMU, including valid tag frame numbers and virtual addresses processed.
User and kernel space integration, memory page partitioning, and physical/virtual address mapping.
32-bit architecture example detailing process VA space, kernel space, and physical address mapping.
Manages access control, dynamic memory allocation, and maintains virtual address spaces for processes.
Optimization of primary/secondary memory through page swapping, maintaining a page cache.
Recap of W's of memory management, partitioning, organization, MMU operation, and Linux specifics.
Open floor for any queries regarding the topics discussed.
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- 1. © 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Linux Memory Management
- 2. 2© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. What to Expect? W's of Memory Management? Memory Partitioning Memory Organization Memory Management in Linux Swapping
- 3. 3© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Why Memory Management? Transition from Uni-process → Multi-process Every process needs its own memory Memory Division Program loaded to “any” available memory address Relocation Independence / Non-interference between Processes Protection Communication between Processes Sharing Process Memory with Attributes (like read only for code) Logical Organization Executing Programs bigger than available Memory Physical Organization (Overlaying & Reusing)
- 4. 4© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. What is Memory Management? Key task: Division of Memory Starting from the Division between OS (Kernel) Application (User) Others follow Relocation, Protection, Sharing Logical & Physical Organization May involve movement between primary & secondary
- 5. 5© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Memory Partitioning Two traditional division mechanisms Segmentation: Unequal sized Examples: Linear Allocation, Buddy System Paging: Equal sized Examples: 4K-Paged Allocation Examples in Linux User-space malloc(): Segmentation Slab sub-system: Paging
- 6. 6© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Pros & Cons Memory Fragmentation External in Segmentation (gets worser) Internal in Paging Space Efficiency Segmentation: More meta but lesser allocation wastage Paging: Negligible meta but significant allocation wastage Time Efficiency Segmentation: Complex search & Storage Algorithm Paging: Simple Algorithms
- 7. 7© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Memory Organization All other needs (Relocation, Protection, Sharing, ...) Beautifully achieved by the concept of virtualization That is organizing the memory into Physical & Virtual Address Spaces And then using the virtual addressing for all purposes Both may use either Paging or Segmentation Best to use similar mechanisms Linux uses Paging for both with 4KiB/8KiB page size Virtualization can be achieved Using special hardware called MMU Using software MMU
- 8. 8© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Memory Organization ... Linux Kernels (>= 2.5.46) support both Earlier kernels worked only with hardware MMU uClinux used to be the solution for non-MMU processors & controllers Latest Intel, ARM, and most other architectures have in-built MMU Older x86, ARM7, and few such doesn't have a hardware MMU
- 9. 9© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Memory (RAM) Working of an MMU 1 1 0 1 Valid Tag Frame Number TLB (in Cache) 1 Page Table (in RAM) 1 1 1 0 1 0 1 1 0 1 Page Number [31:12] Offset [11:0] Virtual Address
- 10. 10© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Memory Management in Linux In Linux, all these combined User Space & Kernel Space Memory Page Partitioning Physical & Virtual Address Spaces Device Addresses, Mapping & Access Takes the following form ...
- 11. 11© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Memory Organization in Linux An Example assuming 32-bit architecture 4GB Process VA Space 1 User Space 4GB Process VA Space N . . . 3GB Virtual Address for User 1GB VA for Kernel Kernel Space (fixed by kernel) Logical Address (Non-swappable) Virtual Address (Swappable) 0x00000000 0xBFFFFFFF 0xFFFFFFFF 0xC0000000 Upto 3GB Memory (RAM) Addressing Upto 1GB Dev Addressing Physical Address Space (fixed by architecture) 0x00000000 0xBFFFFFFF 0xC0000000 0xFFFFFFFF Bus Address (incl. both h/w memory & registers) Physical Address (incl. only memory)
- 12. 12© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Linux Memory Manager Provides Access Control to h/w & memory resources Provides Dynamic Memory to kernel sub-system Drivers File Systems Stacks Provides Virtual Memory to Kernel & User space Kernel & User Processes run in their own virtual address spaces Providing the various features of a Linux system System reliability, Security Communication Program Execution Support
- 13. 13© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Swapping Optimizes primary & secondary memory usage Primary memory pages swapped out When running out of memory Secondary memory pages swapped in When needed back Linux maintains Page Cache in Primary Memory for Code: Reloadable Data: Unchanged vs Changed Changed Data: Temporary (Dynamic) vs Persistent (Files) Linux uses Swap (raw) partition on Secondary Memory Related commands: mkswap, swapon/off
- 14. 14© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. What all have we learnt? W's of Memory Management? Memory Partitioning Segmentation & Paging Memory Organization Physical & Virtual Addressing Working of an MMU Memory Management in Linux Swapping & Swap Partition
- 15. 15© 2010-17 SysPlayWorkshops <workshop@sysplay.in> All Rights Reserved. Any Queries?