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linux内存管理之伙伴系统（建立）
内核使用伙伴系统来解决内存分配引起的外部碎片问题。
一、数据结构描述
结构zone中的free_area数组描述伙伴系统该数组为free_area结构
view plaincopy to clipboard- 01.struct zone {
- 02.……
- 03. struct free_area free_area[MAX_ORDER];
- 04.……
- 05.}；
- 01.struct free_area {/*链表类型为5类，对于分类为新加入的*/
- 02. struct list_head free_list[MIGRATE_TYPES];
- 03. unsigned long nr_free;
- 04.};
二、伙伴系统的初始化
在初始化物理管理区的时候初始化伙伴系统的，具体实现在下面的函数中：- Start_kernel()->setup_arch()->paging_init()->zone_sizes_init()->free_area_init_nodes()->free_area_init_node()->free_area_init_core()->init_currently_empty_zone()->zone_init_free_lists()
- 01./*初始化对应zone中所有order和所有类型的链表*/
- 02.static void __meminit zone_init_free_lists(struct zone *zone)
- 03.{
- 04. int order, t;
- 05. for_each_migratetype_order(order, t) {
- 06. INIT_LIST_HEAD(&zone->free_area[order].free_list[t]);
- 07. zone->free_area[order].nr_free = 0;
- 08. }
- 09.}
将bootmem分配器中的数据回收到伙伴系统中
start_kernel()->mm_init()->mem_init()
view plaincopy to clipboard- 01.void __init mem_init(void)
- 02.{
- 03. int codesize, reservedpages, datasize, initsize;
- 04. int tmp;
- 05./*和具体硬件相关*/
- 06. pci_iommu_alloc();
- 07.
- 08.#ifdef CONFIG_FLATMEM
- 09. BUG_ON(!mem_map);
- 10.#endif
- 11. /* this will put all low memory onto the freelists */
- 12. /*释放bootmem中的内存到伙伴系统中，包括bootmem占有的位图
- 13. 返回总共释放的页面数**/
- 14. totalram_pages += free_all_bootmem();
- 15.
- 16. reservedpages = 0;
- 17. for (tmp = 0; tmp < max_low_pfn; tmp++)
- 18. /*
- 19. * Only count reserved RAM pages:
- 20. */
- 21. if (page_is_ram(tmp) && PageReserved(pfn_to_page(tmp)))
- 22. reservedpages++;
- 23. /*初始化高端内存区，将高端内存区放入伙伴系统中*/
- 24. set_highmem_pages_init();
- 25. /*内核代码段、数据段、初始化端长度*/
- 26. codesize = (unsigned long) &_etext - (unsigned long) &_text;
- 27. datasize = (unsigned long) &_edata - (unsigned long) &_etext;
- 28. initsize = (unsigned long) &__init_end - (unsigned long) &__init_begin;
- 29. /*打印输出各种内存初始化后的信息*/
- 30. printk(KERN_INFO "Memory: %luk/%luk available (%dk kernel code, "
- 31. "%dk reserved, %dk data, %dk init, %ldk highmem)\n",
- 32. nr_free_pages() << (PAGE_SHIFT-10),
- 33. num_physpages << (PAGE_SHIFT-10),
- 34. codesize >> 10,
- 35. reservedpages << (PAGE_SHIFT-10),
- 36. datasize >> 10,
- 37. initsize >> 10,
- 38. (unsigned long) (totalhigh_pages << (PAGE_SHIFT-10))
- 39. );
- 40.
- 41. printk(KERN_INFO "virtual kernel memory layout:\n"
- 42. " fixmap : 0x%08lx - 0x%08lx (%4ld kB)\n"
- 43.#ifdef CONFIG_HIGHMEM
- 44. " pkmap : 0x%08lx - 0x%08lx (%4ld kB)\n"
- 45.#endif
- 46. " vmalloc : 0x%08lx - 0x%08lx (%4ld MB)\n"
- 47. " lowmem : 0x%08lx - 0x%08lx (%4ld MB)\n"
- 48. " .init : 0x%08lx - 0x%08lx (%4ld kB)\n"
- 49. " .data : 0x%08lx - 0x%08lx (%4ld kB)\n"
- 50. " .text : 0x%08lx - 0x%08lx (%4ld kB)\n",
- 51. FIXADDR_START, FIXADDR_TOP,
- 52. (FIXADDR_TOP - FIXADDR_START) >> 10,
- 53.
- 54.#ifdef CONFIG_HIGHMEM
- 55. PKMAP_BASE, PKMAP_BASE+LAST_PKMAP*PAGE_SIZE,
- 56. (LAST_PKMAP*PAGE_SIZE) >> 10,
- 57.#endif
- 58.
- 59. VMALLOC_START, VMALLOC_END,
- 60. (VMALLOC_END - VMALLOC_START) >> 20,
- 61.
- 62. (unsigned long)__va(0), (unsigned long)high_memory,
- 63. ((unsigned long)high_memory - (unsigned long)__va(0)) >> 20,
- 64.
- 65. (unsigned long)&__init_begin, (unsigned long)&__init_end,
- 66. ((unsigned long)&__init_end -
- 67. (unsigned long)&__init_begin) >> 10,
- 68.
- 69. (unsigned long)&_etext, (unsigned long)&_edata,
- 70. ((unsigned long)&_edata - (unsigned long)&_etext) >> 10,
- 71.
- 72. (unsigned long)&_text, (unsigned long)&_etext,
- 73. ((unsigned long)&_etext - (unsigned long)&_text) >> 10);
- 74.
- 75. /*
- 76. * Check boundaries twice: Some fundamental inconsistencies can
- 77. * be detected at build time already.
- 78. */
- 79.#define __FIXADDR_TOP (-PAGE_SIZE)
- 80.#ifdef CONFIG_HIGHMEM
- 81. BUILD_BUG_ON(PKMAP_BASE + LAST_PKMAP*PAGE_SIZE > FIXADDR_START);
- 82. BUILD_BUG_ON(VMALLOC_END > PKMAP_BASE);
- 83.#endif
- 84.#define high_memory (-128UL << 20)
- 85. BUILD_BUG_ON(VMALLOC_START >= VMALLOC_END);
- 86.#undef high_memory
- 87.#undef __FIXADDR_TOP
- 88.
- 89.#ifdef CONFIG_HIGHMEM
- 90. BUG_ON(PKMAP_BASE + LAST_PKMAP*PAGE_SIZE > FIXADDR_START);
- 91. BUG_ON(VMALLOC_END > PKMAP_BASE);
- 92.#endif
- 93. BUG_ON(VMALLOC_START >= VMALLOC_END);
- 94. BUG_ON((unsigned long)high_memory > VMALLOC_START);
- 95.
- 96. if (boot_cpu_data.wp_works_ok < 0)
- 97. test_wp_bit();
- 98.
- 99. save_pg_dir();
- 100. /*调用zap_low_mappings函数清low_memory的映射，内核线程只访问内核空间是不能访问用户空间的
- 101. ，其实low_memory的映射被设置的部分也就是当初为
- 102. 8MB建立的恒等映射填充了临时内核页全局目录的第0项，第1项
- 103. 这里将用户空间的页目录项<3G的PGD清0；*/
- 104. zap_low_mappings(true);
- 105.}
- 01./**
- 02. * free_all_bootmem - release free pages to the buddy allocator
- 03. *
- 04. * Returns the number of pages actually released.
- 05. */
- 06.unsigned long __init free_all_bootmem(void)
- 07.{
- 08. return free_all_bootmem_core(NODE_DATA(0)->bdata);
- 09.}
- 01.static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
- 02.{
- 03. int aligned;
- 04. struct page *page;
- 05. unsigned long start, end, pages, count = 0;
- 06.
- 07. if (!bdata->node_bootmem_map)
- 08. return 0;
- 09. /*节点内存开始和结束处*/
- 10. start = bdata->node_min_pfn;
- 11. end = bdata->node_low_pfn;
- 12.
- 13. /*
- 14. * If the start is aligned to the machines wordsize, we might
- 15. * be able to free pages in bulks of that order.
- 16. */
- 17. aligned = !(start & (BITS_PER_LONG - 1));
- 18.
- 19. bdebug("nid=%td start=%lx end=%lx aligned=%d\n",
- 20. bdata - bootmem_node_data, start, end, aligned);
- 21. /*用于释放整个bootmem所涉及的内存*/
- 22. while (start < end) {
- 23. unsigned long *map, idx, vec;
- 24.
- 25. map = bdata->node_bootmem_map;
- 26. idx = start - bdata->node_min_pfn;/*相对于开始处的偏移*/
- 27. vec = ~map[idx / BITS_PER_LONG];/*vec值为页面分配情况*/
- 28. /*如果开始地址以32位对其、连续的32个页面都没有被分配(空闲),并且
- 29. 释放起点以上的32个页面都是合法的(不超过end值)，则释放连续的32个
- 30. 页面，即1<<5个页面*/
- 31. if (aligned && vec == ~0UL && start + BITS_PER_LONG < end) {
- 32. int order = ilog2(BITS_PER_LONG);/*32位下为5*/
- 33. /*释放到伙伴系统中*/
- 34. __free_pages_bootmem(pfn_to_page(start), order);
- 35. count += BITS_PER_LONG;/*释放的总页面数更新*/
- 36. } else {
- 37. unsigned long off = 0;
- 38. /*vec!=0表示这个区间存在页面空闲，off为这个区间的下标，从0开始*/
- 39. while (vec && off < BITS_PER_LONG) {
- 40. if (vec & 1) {/*如果页面空闲*/
- 41. /*偏移转化为具体的页面*/
- 42. page = pfn_to_page(start + off);
- 43. /*一个页面一个页面的释放*/
- 44. __free_pages_bootmem(page, 0);/*释放单个页面*/
- 45. count++;/*更新释放页面总数*/
- 46. }
- 47. vec >>= 1;/*vec向右移动一位，表示访问下一个页面*/
- 48. off++;/*偏移加一*/
- 49. }
- 50. }
- 51. start += BITS_PER_LONG;/*偏移向后移动*/
- 52. }
- 53. /*虚拟地址转化为page
- 54. 用于释放bdata中的位图所占有的内存*/
- 55. page = virt_to_page(bdata->node_bootmem_map);
- 56. pages = bdata->node_low_pfn - bdata->node_min_pfn;
- 57.
- 58. /*计算bootmem分配器中所使用的页面数,即位图使用的页面数*/
- 59. pages = bootmem_bootmap_pages(pages);
- 60. count += pages;/*释放的总页面数加*/
- 61. while (pages--)/*每次释放一个页面，释放
- 62. 总共的pages个页面*/
- 63. __free_pages_bootmem(page++, 0);
- 64.
- 65. bdebug("nid=%td released=%lx\n", bdata - bootmem_node_data, count);
- 66.
- 67. return count;/*返回释放的总页面数*/
- 68.}
- 01./*
- 02. * permit the bootmem allocator to evade page validation on high-order frees
- 03. */
- 04.void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
- 05.{
- 06. if (order == 0) {
- 07. __ClearPageReserved(page);
- 08. set_page_count(page, 0);/*设置页面的引用位为0*/
- 09. set_page_refcounted(page);/*设置页面的引用位为1*/
- 10. __free_page(page);/*释放单个页面到伙伴系统中*/
- 11. } else {
- 12. int loop;
- 13.
- 14. /*这个不是很明白，可能和特定的体系相关???*/
- 15. prefetchw(page);
- 16. for (loop = 0; loop < BITS_PER_LONG; loop++) {
- 17. struct page *p = &page[loop];
- 18.
- 19. if (loop + 1 < BITS_PER_LONG)
- 20. prefetchw(p + 1);
- 21. __ClearPageReserved(p);
- 22. set_page_count(p, 0);
- 23. }
- 24.
- 25. set_page_refcounted(page);/*设置页面的引用计数为1*/
- 26. /*这里具体释放到那个类型里面，
- 27. 要看page的里面具体的东西，也就是
- 28. 可以用相关函数来获取他所属的类型*/
- 29. __free_pages(page, order);/*释放order个页面*/
- 30. }
- 31.}
- 01.void __init set_highmem_pages_init(void)
- 02.{
- 03. struct zone *zone;
- 04. int nid;
- 05.
- 06. for_each_zone(zone) {
- 07. unsigned long zone_start_pfn, zone_end_pfn;
- 08.
- 09. if (!is_highmem(zone))/*验证是否属于高端内存区域中*/
- 10. /*如果不属于，将不执行下面的操作*/
- 11. continue;
- 12.
- 13. zone_start_pfn = zone->zone_start_pfn;
- 14. zone_end_pfn = zone_start_pfn + zone->spanned_pages;
- 15. /*返回zone中的node的id*/
- 16. nid = zone_to_nid(zone);
- 17. printk(KERN_INFO "Initializing %s for node %d (%08lx:%08lx)\n",
- 18. zone->name, nid, zone_start_pfn, zone_end_pfn);
- 19. /*将区间中的内存放到伙伴系统中*/
- 20. add_highpages_with_active_regions(nid, zone_start_pfn,
- 21. zone_end_pfn);
- 22. }
- 23. totalram_pages += totalhigh_pages;
- 24.｝
- 01.void __init add_highpages_with_active_regions(int nid, unsigned long start_pfn,
- 02. unsigned long end_pfn)
- 03.{
- 04. struct add_highpages_data data;
- 05.
- 06. data.start_pfn = start_pfn;
- 07. data.end_pfn = end_pfn;
- 08. /*对节点中的每个区域进行页面的回收到伙伴系统中*/
- 09. work_with_active_regions(nid, add_highpages_work_fn, &data);
- 10.}
- 01./*用指定函数来操作活动区，在高端内存初始化时用了*/
- 02.void __init work_with_active_regions(int nid, work_fn_t work_fn, void *data)
- 03.{
- 04. int i;
- 05. int ret;
- 06.
- 07. for_each_active_range_index_in_nid(i, nid) {
- 08. ret = work_fn(early_node_map[i].start_pfn,
- 09. early_node_map[i].end_pfn, data);
- 10. if (ret)
- 11. break;
- 12. }
- 13.}
- 01.static int __init add_highpages_work_fn(unsigned long start_pfn,
- 02. unsigned long end_pfn, void *datax)
- 03.{
- 04. int node_pfn;
- 05. struct page *page;
- 06. unsigned long final_start_pfn, final_end_pfn;
- 07. struct add_highpages_data *data;
- 08.
- 09. data = (struct add_highpages_data *)datax;
- 10. /*活动内存区间与指定考虑区间交集*/
- 11. final_start_pfn = max(start_pfn, data->start_pfn);
- 12. final_end_pfn = min(end_pfn, data->end_pfn);
- 13. if (final_start_pfn >= final_end_pfn)
- 14. return 0;
- 15.
- 16. for (node_pfn = final_start_pfn; node_pfn < final_end_pfn;
- 17. node_pfn++) {
- 18. if (!pfn_valid(node_pfn))/*验证页面是否有效*/
- 19. continue;
- 20. page = pfn_to_page(node_pfn);/*将下标转换为具体的页面*/
- 21. /*初始化页面的count值，将页面释放到伙伴系统中*/
- 22. add_one_highpage_init(page, node_pfn);
- 23. }
- 24.
- 25. return 0;
- 26.
- 27.}
- 01.static void __init add_one_highpage_init(struct page *page, int pfn)
- 02.{
- 03. /*ClearPageReserved清除了该页面flag中的reserved标志，表示该页面属于动态内存*/
- 04. ClearPageReserved(page);
- 05. init_page_count(page);/*设置page的count值为1*/
- 06. __free_page(page); /*释放页面到伙伴系统*/
- 07. totalhigh_pages++;/*更新高端页面总数*/
- 08.}
- 01.void zap_low_mappings(bool early)
- 02.{
- 03. int i;
- 04.
- 05. /*
- 06. * Zap initial low-memory mappings.
- 07. *
- 08. * Note that "pgd_clear()" doesn't do it for
- 09. * us, because pgd_clear() is a no-op on i386.
- 10. */
- 11. /*这个函数很简单，就是把前面我们在arch/x86/kernel/head_32.S中设置的页全局目录的前若干项清零
- 12. 。这若干项到底是多少
- 13. 不错，0xc0000000>>22 & 1023= 768，这些也全局目录项代表虚拟地址前3G的页面，也就是所谓的用户区
- 14. ，我们在这里把它全清零了。*/
- 15. for (i = 0; i < KERNEL_PGD_BOUNDARY; i++) {
- 16.#ifdef CONFIG_X86_PAE
- 17. set_pgd(swapper_pg_dir+i, __pgd(1 + __pa(empty_zero_page)));
- 18.#else
- 19. set_pgd(swapper_pg_dir+i, __pgd(0));
- 20.#endif
- 21. }
- 22.
- 23. if (early)
- 24. __flush_tlb();
- 25. else
- 26. flush_tlb_all();
- 27.}
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发表于 2012-01-08 21:58
