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![Buddy System
zone descriptor
free_area[10] 1024 pages ……
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free_area[11]
free_area[4]
free_area[3]
free_area[2] 4 pages ……
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free_area[1] 2 pages 2 pages ……
free_area[0] 1 page 1 page 1 page ……
12/4/26 Linux - Memory Management 13](https://image.slidesharecdn.com/mm-121212232739-phpapp02/85/Linux-Memory-Management-13-320.jpg)
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Linux Memory Management
This document discusses Linux memory management. It outlines the buddy system, zone allocation, and slab allocator used by Linux to manage physical memory. It describes how pages are allocated and initialized at boot using the memory map. The slab allocator is used to optimize allocation of kernel objects and is implemented as caches of fixed-size slabs and objects. Per-CPU allocation improves performance by reducing locking and cache invalidations.
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Linux Memory Management
- 1. Linux – Memory Management D3 Tsung-Han “Johnny” Lin
- 2. 12/4/26 Linux - Memory Management 2
- 3. Outline • Memory in Linux – Dynamic Allocation – Contiguous Allocation •Memory Allocation – Buddy System – Zone – SLAB Allocator • Per-CPU data 12/4/26 Linux - Memory Management 3
- 4. MMU - SimpleHistory Early Linux on x86 Linux 2.5.46 (MMU) Embedded Developer?! µClinux (Linux for microconcroller) Jeff Dionne et al.1998 12/4/26 Linux - Memory Management 4
- 5. All about PAGE •Physical page -> page frame – Page descriptor, page – All pages, mem_map 12/4/26 Linux - Memory Management 5
- 6. Initialization query or invoke Kernel BIOS machine_specific_memory_setup() setup_memory_map() struct page* mem_map Physical Memory 12/4/26 Linux - Memory Management 6
- 7. Memory 12/4/26 Linux - Memory Management 7
- 8. How pages areallocated? 12/4/26 Linux - Memory Management 8
- 9. Kernel API • alloc_pages •__get_free_pages • kmalloc • … • But, seriously 12/4/26 Linux - Memory Management 9
- 10. HOW? 12/4/26 Linux - Memory Management 10
- 11. Hierarchy Overview App w/glibc heap Zone Allocator Slab Allocator glibc Buddy Allocator MMU Kernel Physical Subsystems VM Subsystem Memory kswapd App w/ heap bdflush Disk Driver User Space Kernel Space Disk 12/4/26 Linux - Memory Management 11
- 12. Memory Zone Physical Memory(mem_map) 0x37999999, 896MB ZONE_DMA ZONE_NORMAL ZONE_HIGHMEM 12/4/26 0x01000000, 16MB Linux - Memory Management 12 0x40000000, 1GB
- 13. Buddy System zone descriptor free_area[10] 1024 pages …… ……… ……… ……… free_area[11] free_area[4] free_area[3] free_area[2] 4 pages …… ……… free_area[1] 2 pages 2 pages …… free_area[0] 1 page 1 page 1 page …… 12/4/26 Linux - Memory Management 13
- 14. Zone, again • ZONE_DMA,0 ~ 16 MB 896MB ?! • ZONE_NORMAL, 16 MB ~ 896 MB • ZONE_HIGHMEM, rest of them … 12/4/26 Linux - Memory Management 14
- 15. Kernel View Linear – 4 GB Physical TASK_SIZE 0x0 3 GB PAGE_OFFSET ZONE_HIGHMEM 0xc0000000 0x40000000, 1GB Kernel 8 MB Image Reserved 0x37999999, 896MB mem_map 128 MB ZONE_NORMAL 1 GB … 0x01000000, 16MB 896 MB ZONE_NORMAL ZONE_DMA + ZONE_DMA 0xffffffff 12/4/26 Linux - Memory Management 15
- 16. Do we needthis large?! 12/4/26 Linux - Memory Management 16
- 17. SLAB Allocator • Firstintroduced in 大辞泉 SunOS 5.4 slab/slǽb/ • Implemented in Linux 名 詞 2.2 1 （石木材金属などの）広い厚板；（材木 の）背板. • SLAB system 2 （食べ物などの）厚切り – SLAB a thick slab of apple pie｜厚切りのアップル パイ. – SLOB, embedded system 3｟ 俗語｟ 〘野球〙ピッチャーズプレート. – SLUB, efficient ver. 4｟ ～｟｟ the 俗語｟ （病院などの）死体置 き台 – SLQB, per-CPU scaling on the slab｜（死体となって）安置されて. • kmalloc()! 12/4/26 Linux - Memory Management Cache !! 17
- 18. Design of SLAB cache_chain slab_full …… page struct cache slab slab object Page 1 page … cache slab_partial slab (kmem_cache) object page … slab object Page 2 cache page slab_partial …… 12/4/26 Linux - Memory Management 18
- 19. Per-CPU Allocation • Request/Release single page – Frequently • Per-CPU – Reducing cache invalidation – Reducing locking – A simple data array • In 2.4 kernel – get_cpu(), preemption disabled – Access array directly • In 2.6 kernel – Wrapper – percpu interface – Cache alignment 12/4/26 Linux - Memory Management 19
- 20. Review App w/ glibcheap Zone Allocator Slab Allocator glibc Buddy Allocator MMU Kernel Physical Subsystems VM Subsystem Memory kswapd App w/ heap bdflush Disk Driver User Space Kernel Space Disk 12/4/26 Linux - Memory Management 20
- 21. Reference • Linux KernelDevelopment, 3rd • Understanding the Linux Kernel, 3rd – http://www.makelinux.net/books/ulk3/t oc • Understanding the Virtual Memory Manager – http://www.kernel.org/doc/gorman/htm l/understand/index.html 12/4/26 Linux - Memory Management 21