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![7
Virtual memory
description• Address space (struct mm_struct)
• VM area (struct vm_area_struct)
$ cat /proc/self/maps
00400000-0040c000 r-xp 00000000 08:03 2359718 /usr/bin/cat
0060b000-0060c000 r--p 0000b000 08:03 2359718 /usr/bin/cat
0060c000-0060d000 rw-p 0000c000 08:03 2359718 /usr/bin/cat
011a7000-011c8000 rw-p 00000000 00:00 0 [heap]
7f4d072e5000-7f4d0d80e000 r--p 00000000 08:03 2369473
/usr/lib/locale/locale-archive
7f4d0d80e000-7f4d0d9c2000 r-xp 00000000 08:03 2366682 /usr/lib64/libc-2.18.so
7f4d0d9c2000-7f4d0dbc2000 ---p 001b4000 08:03 2366682 /usr/lib64/libc-2.18.so
7f4d0dbc2000-7f4d0dbc6000 r--p 001b4000 08:03 2366682 /usr/lib64/libc-2.18.so
...](https://image.slidesharecdn.com/mm32-140804040715-phpapp02/85/Memory-management-in-Linux-kernel-7-320.jpg)
![14
Memory pressure
balancing
• nr_pages_to_scan =
nr_pages/2^priority
• priority = [12..0]
1/4096, 1/2048, 1/1024, ...
• swappiness
• active > inactive](https://image.slidesharecdn.com/mm32-140804040715-phpapp02/85/Memory-management-in-Linux-kernel-14-320.jpg)
Uploaded byVadim Nikitin
Memory management in Linux kernel
The document provides an overview of memory management in the Linux kernel, covering various components such as physical and virtual memory allocation, page replacement, and the memory reclaim process. It details the hardware support, API calls for both kernel and user space, as well as monitoring tools and cgroup memory management. Additionally, it addresses specific challenges and solutions regarding memory management, including compaction and the implementation of various limits and controls.
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Memory management in Linux kernel
- 1.
- 2.
- 3. 3 Memory management tasks • Physicalmemory allocator • Physical memory management • Virtual memory allocator • PTE management • Memory allocator for kernel needs
- 4. 4 Memory management subsystem • >100Klines • Buddy allocator • Page replacement (“LRU” reclaim model) • PTE management • Slab/slob/slub kernel allocator • Pagecache/writeback/readahead/swap • Cgroup memory controller • Compaction
- 5. 5 Hardware • X86_64 • Paging(MMU, TLB, ...) • 4KB, 2MB and 1GB pages • NUMA • 4-level PTE's • Hardware referenced bit
- 6. 6 Physical memory description • Node(pg_data_t) • Zone (struct zone) • Page (struct page) $ cat /proc/zoneinfo | grep Node Node 0, zone DMA Node 0, zone DMA32 Node 0, zone Normal Node 1, zone Normal
- 7. 7 Virtual memory description• Addressspace (struct mm_struct) • VM area (struct vm_area_struct) $ cat /proc/self/maps 00400000-0040c000 r-xp 00000000 08:03 2359718 /usr/bin/cat 0060b000-0060c000 r--p 0000b000 08:03 2359718 /usr/bin/cat 0060c000-0060d000 rw-p 0000c000 08:03 2359718 /usr/bin/cat 011a7000-011c8000 rw-p 00000000 00:00 0 [heap] 7f4d072e5000-7f4d0d80e000 r--p 00000000 08:03 2369473 /usr/lib/locale/locale-archive 7f4d0d80e000-7f4d0d9c2000 r-xp 00000000 08:03 2366682 /usr/lib64/libc-2.18.so 7f4d0d9c2000-7f4d0dbc2000 ---p 001b4000 08:03 2366682 /usr/lib64/libc-2.18.so 7f4d0dbc2000-7f4d0dbc6000 r--p 001b4000 08:03 2366682 /usr/lib64/libc-2.18.so ...
- 8. 8 File mappings • Filemappings (struct address_space) • Radix tree with all resident pages • Pagecache • Major/minor pagefault
- 9. 9 Kernel API • __get_free_page() •kmalloc()/kfree() • vmalloc() • ...
- 10. 10 Userspace API • pagefault •mmap()/munmap() • brk() • mlock()/munlock() • fadvise(), madvise() • ...
- 11. 11 Memory reclaim • Normal/directreclaim (free pool) • Per-node kswapd • Working set • Memory pressure • File memory vs anonymous memory • Swap • OOM
- 12. 12 “LRU” model • 5double linked lists: inactive file, active file, inactive anon, active anon, unevictable • Referenced flag in struct page_struct flag
- 13. 13 List transition rules •mark_page_accessed(): – unreferenced -> referenced – inactive && referenced -> active • shrink_inactive_list(): – if (ptes referenced) • anonymous -> active • referenced -> active • (ptes referenced > 1) -> active (3.2) • (vm_flags & VM_EXEC) -> active (3.2) • set referenced • rotate – else • reclaim • shrink_active_list(): – If referenced • file & VM_EXEC -> rotate – -> inactive
- 14. 14 Memory pressure balancing • nr_pages_to_scan= nr_pages/2^priority • priority = [12..0] 1/4096, 1/2048, 1/1024, ... • swappiness • active > inactive
- 15. 15 Yasearch-specific problems & solutions •Working set > 1/2 available memory • Memory thrashing • promote_mapped_pages • file_inactive_ratio
- 16. 16 Monitoring & tools •top • vmtouch • /proc/vmstat • /proc/buddyinfo • /proc/slabinfo • perf top • oom-message in dmesg
- 17.
- 18. 18 Cgroups • Each cgrouphas own LRU lists. • No common LRU (since 3.3)! • Common free pool(s) • Common kswapd thread(s) • Global reclaim vs target reclaim
- 19. 19 Memory controller • memory.limit_in_bytes •memory.soft_limit_in_bytes (will be deprecated) • memory.use_hierarchy • ...
- 20.
- 21. 21 Accounting • Each pagebelongs to one cgroup • First accessed - owner • memory.move_charge_at_immigr ate
- 22. 22 Yasearch-specific problems & solutions •memory.low_limit_in_bytes • First accessed – owner? mlock()? low_limit? • memory.recharge_on_pgfault
- 23. 23 Compaction • Physical pagesmigration to zone's top • https://lwn.net/Articles/368869 • Broken in 3.3-3.7 • Replacement for lumpy reclaim • Use perf top for problem diagnostics
- 24.