linux物理内存管理区初始化

发布时间：2014-09-05 16:38:01作者：知识屋

Linux物理内存管理区在start_kernel函数中进行初始化，此时启动分配器已经建立，所以可以从bootmem中分配需要的内存。

一、全局变量初始化

max_pfn：最大物理页面帧号

start_kernel()->setup_arch()->e820_end_of_ram_pfn()找出最大可用内存页面帧号。

void __init setup_arch(char **cmdline_p)
{
    ……
/*
     * partially used pages are not usable - thus
     * we are rounding upwards:
     */
    /*遍历e820.map，找到系统中得最大内存数，
    这个内存数需小于4G*/
    max_pfn = e820_end_of_ram_pfn();
    ……
｝

unsigned long __init e820_end_of_ram_pfn(void)
{
    /*MAX_ARCH_PFN为4G空间*/
    return e820_end_pfn(MAX_ARCH_PFN, E820_RAM);
}

/*
* Find the highest page frame number we have available
*/
static unsigned long __init e820_end_pfn(unsigned long limit_pfn, unsigned type)
{
    int i;
    unsigned long last_pfn = 0;
    unsigned long max_arch_pfn = MAX_ARCH_PFN;/*4G地址空间对应的页面数*/

   /*对e820中所有的内存块,其中e820为从bios中探测到的页面数存放处*/
    for (i = 0; i < e820.nr_map; i++) {
        struct e820entry *ei = &e820.map[i];/*第i个物理页面块*/
        unsigned long start_pfn;
        unsigned long end_pfn;

        if (ei->type != type)/*与找的类型不匹配*/
            continue;
        /*起始地址对应的页面帧号*/
        start_pfn = ei->addr >> PAGE_SHIFT;
        /*结束物理地址对应的页面帧号*/
        end_pfn = (ei->addr + ei->size) >> PAGE_SHIFT;

        if (start_pfn >= limit_pfn)
            continue;
        if (end_pfn > limit_pfn) {
            last_pfn = limit_pfn;/*找到的结束页面帧号大于限制大小时*/
            break;
        }
        if (end_pfn > last_pfn)
            last_pfn = end_pfn;/*保存更新last_pfn*/
    }

    if (last_pfn > max_arch_pfn)/*大于4G空间时*/
        last_pfn = max_arch_pfn;
    /*打印输出信息*/
    printk(KERN_INFO "last_pfn = %#lx max_arch_pfn = %#lx/n",
             last_pfn, max_arch_pfn);
    /*返回最后一个页面帧号*/
    return last_pfn;
}
max_low_pfn：低端内存最大页面数

start_kernel()->setup_arch()->find_low_pfn_range()

/*
* Determine low and high memory ranges:
*/
/*找到低端内存的做大内存页面数，初始化两个变量*/
void __init find_low_pfn_range(void)
{
    /* it could update max_pfn */
    /*当内存的大小本来就小于低端内存的做大页框数时；
    直接没有高端地址映射*/
    if (max_pfn <= MAXMEM_PFN)
        lowmem_pfn_init();
    else/*这是一般PC机的运行流程，存在高端映射*/
        highmem_pfn_init();
}
我们直接看具有高端地址空间的部分。

/*
* We have more RAM than fits into lowmem - we try to put it into
* highmem, also taking the highmem=x boot parameter into account:
*/
/*高端地址空间的页面数可以在启动中进行配置；
如果不配置，在这里进行设置大小*/
void __init highmem_pfn_init(void)
{
    /*MAXMEM_PFN为最大物理地址-(4M+4M+8K+128M);
    所以低端内存的大小其实比我们说的896M低一些*/
    max_low_pfn = MAXMEM_PFN;

    if (highmem_pages == -1)/*高端内存页面数如果在开机没有设置*/
        highmem_pages = max_pfn - MAXMEM_PFN;/*总页面数减去低端页面数*/
    /*如果highmem_pages变量在启动项设置了，那么在这里就要进行这样的判断，因为可能出现不一致的情况*/
    if (highmem_pages + MAXMEM_PFN < max_pfn)
        max_pfn = MAXMEM_PFN + highmem_pages;

    if (highmem_pages + MAXMEM_PFN > max_pfn) {
        printk(KERN_WARNING MSG_HIGHMEM_TOO_SMALL,
            pages_to_mb(max_pfn - MAXMEM_PFN),
            pages_to_mb(highmem_pages));
        highmem_pages = 0;
    }
#ifndef CONFIG_HIGHMEM
    /* Maximum memory usable is what is directly addressable */
    printk(KERN_WARNING "Warning only %ldMB will be used./n", MAXMEM>>20);
    if (max_pfn > MAX_NONPAE_PFN)
        printk(KERN_WARNING "Use a HIGHMEM64G enabled kernel./n");
    else
        printk(KERN_WARNING "Use a HIGHMEM enabled kernel./n");
    max_pfn = MAXMEM_PFN;
#else /* !CONFIG_HIGHMEM *//*存在高端地址情况*/
#ifndef CONFIG_HIGHMEM64G
    /*在没有配置64G的情况下，内存的大小不能超过4G*/
  if (max_pfn > MAX_NONPAE_PFN) {
        max_pfn = MAX_NONPAE_PFN;
        printk(KERN_WARNING MSG_HIGHMEM_TRIMMED);
    }
#endif /* !CONFIG_HIGHMEM64G */
#endif /* !CONFIG_HIGHMEM */
}
二、管理区初始化

Start_kernl()->setup_arch()->paging_init()->zone_sizes_init()

static void __init zone_sizes_init(void)
{
    /*初始化几个内存区中的最大页面数，在后面用于具体的初始化工作*/
    unsigned long max_zone_pfns[MAX_NR_ZONES];
    memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
    max_zone_pfns[ZONE_DMA] =/*DMA区的最大页面帧号，后面的类似*/
        virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT;
    max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
#ifdef CONFIG_HIGHMEM
    max_zone_pfns[ZONE_HIGHMEM] = highend_pfn;
#endif
    /*内存体系的MMU建立，包括伙伴系统的初步建立*/
    free_area_init_nodes(max_zone_pfns);
}
其中x86-32 非PAE下MAX_DMA_ADDRESS为16M+3G大小

/* The maximum address that we can perform a DMA transfer to on this platform */
#define MAX_DMA_ADDRESS      (PAGE_OFFSET + 0x1000000)

/**
* free_area_init_nodes - Initialise all pg_data_t and zone data
* @max_zone_pfn: an array of max PFNs for each zone
*
* This will call free_area_init_node() for each active node in the system.
* Using the page ranges provided by add_active_range(), the size of each
* zone in each node and their holes is calculated. If the maximum PFN
* between two adjacent zones match, it is assumed that the zone is empty.
* For example, if arch_max_dma_pfn == arch_max_dma32_pfn, it is assumed
* that arch_max_dma32_pfn has no pages. It is also assumed that a zone
* starts where the previous one ended. For example, ZONE_DMA32 starts
* at arch_max_dma_pfn.
*/
void __init free_area_init_nodes(unsigned long *max_zone_pfn)
{
    unsigned long nid;
    int i;

    /* Sort early_node_map as initialisation assumes it is sorted */

    /*将活动区域进行排序，关于活动区域在后面会有介绍*/
    sort_node_map();

    /* Record where the zone boundaries are */
   memset(arch_zone_lowest_possible_pfn, 0,
                sizeof(arch_zone_lowest_possible_pfn));
    memset(arch_zone_highest_possible_pfn, 0,
                sizeof(arch_zone_highest_possible_pfn));

    /*找出活动内存中最小的页面，在代码中的作者的注释很详细*/
   arch_zone_lowest_possible_pfn[0] = find_min_pfn_with_active_regions();
    arch_zone_highest_possible_pfn[0] = max_zone_pfn[0];
    for (i = 1; i < MAX_NR_ZONES; i++) {
        if (i == ZONE_MOVABLE)
            continue;
        arch_zone_lowest_possible_pfn[i] =
            arch_zone_highest_possible_pfn[i-1];/*假定区域连续,下一个区域的最小页面为上一个区的最后页面*/
        arch_zone_highest_possible_pfn[i] =
            max(max_zone_pfn[i], arch_zone_lowest_possible_pfn[i]);
    }
    /*对ZONE_MOVABLE区域设置为0*/
    arch_zone_lowest_possible_pfn[ZONE_MOVABLE] = 0;
    arch_zone_highest_possible_pfn[ZONE_MOVABLE] = 0;

    /* Find the PFNs that ZONE_MOVABLE begins at in each node */
    memset(zone_movable_pfn, 0, sizeof(zone_movable_pfn));
    find_zone_movable_pfns_for_nodes(zone_movable_pfn);/*找出每个区的movable的页面数，关于movable为新引入的机制，在后面的文章中会对其详细分析*/

    /* Print out the zone ranges */
    printk("Zone PFN ranges:/n");
    for (i = 0; i < MAX_NR_ZONES; i++) {
        if (i == ZONE_MOVABLE)
            continue;
        printk(" %-8s %0#10lx -> %0#10lx/n",
                zone_names[i],
                arch_zone_lowest_possible_pfn[i],
                arch_zone_highest_possible_pfn[i]);
    }

    /* Print out the PFNs ZONE_MOVABLE begins at in each node */
    printk("Movable zone start PFN for each node/n");
    for (i = 0; i < MAX_NUMNODES; i++) {
        if (zone_movable_pfn[i])
            printk(" Node %d: %lu/n", i, zone_movable_pfn[i]);
    }

    /* Print out the early_node_map[] */
    printk("early_node_map[%d] active PFN ranges/n", nr_nodemap_entries);
    for (i = 0; i < nr_nodemap_entries; i++)
        printk(" %3d: %0#10lx -> %0#10lx/n", early_node_map[i].nid,
                        early_node_map[i].start_pfn,
                        early_node_map[i].end_pfn);

    /* Initialise every node */
    /*调试用*/
    mminit_verify_pageflags_layout();
    setup_nr_node_ids();

    for_each_online_node(nid) {
        pg_data_t *pgdat = NODE_DATA(nid);

    /*zone中数据的初始化，伙伴系统建立但是没有页面
        和数据，页面在后面的mem_init中得到*/
        free_area_init_node(nid, NULL,
                find_min_pfn_for_node(nid), NULL);

        /* Any memory on that node */
        if (pgdat->node_present_pages)
            node_set_state(nid, N_HIGH_MEMORY);
    /*内存的相关检查*/
        check_for_regular_memory(pgdat);
    }
}

void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
        unsigned long node_start_pfn, unsigned long *zholes_size)
{
    pg_data_t *pgdat = NODE_DATA(nid);

    pgdat->node_id = nid;
    pgdat->node_start_pfn = node_start_pfn;/*这个在前面调用一个函数得到*/
    /*计算系统中节点nid的所有物理页面保存在数据结构中*/
    calculate_node_totalpages(pgdat, zones_size, zholes_size);
    /*当节点只有一个时，将节点的map保存到全局变量中*/
    alloc_node_mem_map(pgdat);
#ifdef CONFIG_FLAT_NODE_MEM_MAP
    printk(KERN_DEBUG "free_area_init_node: node %d, pgdat %08lx, node_mem_map %08lx/n",
        nid, (unsigned long)pgdat,
        (unsigned long)pgdat->node_mem_map);
#endif
    /*zone中相关数据的初始化，包括伙伴系统，等待队列，相关变量，
    数据结构、链表等；*/
    free_area_init_core(pgdat, zones_size, zholes_size);
}
具体的区域的初始化在下面函数进行

/*
* Set up the zone data structures:
*   - mark all pages reserved
*   - mark all memory queues empty
*   - clear the memory bitmaps
*/
static void __paginginit free_area_init_core(struct pglist_data *pgdat,
        unsigned long *zones_size, unsigned long *zholes_size)
{
    enum zone_type j;
    int nid = pgdat->node_id;
    unsigned long zone_start_pfn = pgdat->node_start_pfn;
    int ret;

    pgdat_resize_init(pgdat);
    pgdat->nr_zones = 0;
    init_waitqueue_head(&pgdat->kswapd_wait);
    pgdat->kswapd_max_order = 0;
    pgdat_page_cgroup_init(pgdat);

    for (j = 0; j < MAX_NR_ZONES; j++) {
        struct zone *zone = pgdat->node_zones + j;
        unsigned long size, realsize, memmap_pages;
        enum lru_list l;
    /*下面的两个函数会获得指定节点的真实内存大小*/
        size = zone_spanned_pages_in_node(nid, j, zones_size);
        realsize = size - zone_absent_pages_in_node(nid, j,
                                zholes_size);

        /*
         * Adjust realsize so that it accounts for how much memory
         * is used by this zone for memmap. This affects the watermark
         * and per-cpu initialisations
         */
        memmap_pages =/*存放页面所需要的内存大小*/
            PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
        if (realsize >= memmap_pages) {
            realsize -= memmap_pages;
            if (memmap_pages)
                printk(KERN_DEBUG
                       " %s zone: %lu pages used for memmap/n",
                       zone_names[j], memmap_pages);
        } else
            printk(KERN_WARNING
                " %s zone: %lu pages exceeds realsize %lu/n",
                zone_names[j], memmap_pages, realsize);

        /* Account for reserved pages */
        if (j == 0 && realsize > dma_reserve) {
            realsize -= dma_reserve;/*减去为DMA保留的页面*/
            printk(KERN_DEBUG " %s zone: %lu pages reserved/n",
                    zone_names[0], dma_reserve);
       }

        if (!is_highmem_idx(j))/*如果不是高端内存区*/                                    nr_kernel_pages += realsize;
        nr_all_pages += realsize;
    /*下面为初始化zone结构的相关变量*/
        zone->spanned_pages = size;
        zone->present_pages = realsize;
#ifdef CONFIG_NUMA
        zone->node = nid;
        zone->min_unmapped_pages = (realsize*sysctl_min_unmapped_ratio)
                        / 100;
        zone->min_slab_pages = (realsize * sysctl_min_slab_ratio) / 100;
#endif
        zone->name = zone_names[j];
        spin_lock_init(&zone->lock);
        spin_lock_init(&zone->lru_lock);
        zone_seqlock_init(zone);
        zone->zone_pgdat = pgdat;

        zone->prev_priority = DEF_PRIORITY;

        zone_pcp_init(zone);
        for_each_lru(l) {//初始化链表
            INIT_LIST_HEAD(&zone->lru[l].list);
            zone->reclaim_stat.nr_saved_scan[l] = 0;
        }
        zone->reclaim_stat.recent_rotated[0] = 0;
        zone->reclaim_stat.recent_rotated[1] = 0;
        zone->reclaim_stat.recent_scanned[0] = 0;
        zone->reclaim_stat.recent_scanned[1] = 0;
        zap_zone_vm_stats(zone);/*将变量zone->vm_stat变量置0*/
        zone->flags = 0;
        if (!size)
            continue;
   /*需要定义相关宏该版本没定义*/
        set_pageblock_order(pageblock_default_order());
    /zone中变量pageblock_flags内存申请，从启动分配器中*/
        setup_usemap(pgdat, zone, size);
    /*zone中的任务等待队列和zone的伙伴系统(MAX_ORDER个链表)的初始化，关于伙伴系统将单独在后面总结*/
        ret = init_currently_empty_zone(zone, zone_start_pfn,
                        size, MEMMAP_EARLY);
        BUG_ON(ret);
        /*zone中page相关属性的初始化工作*/
        memmap_init(size, nid, j, zone_start_pfn);
        zone_start_pfn += size;
    }
}
三、分配内存的备用区域初始化(非CONFIG_NUMA）

数据结构表示

x;      /* zone_idx(zoneref->zone) */
};

/*
* One allocation request operates on a zonelist. A zonelist
* is a list of zones, the first one is the 'goal' of the
* allocation, the other zones are fallback zones, in decreasing
* priority.
*
* If zlcache_ptr is not NULL, then it is just the address of zlcache,
* as explained above. If zlcache_ptr is NULL, there is no zlcache.
* *
* To speed the reading of the zonelist, the zonerefs contain the zone index
* of the entry being read. Helper functions to access information given
* a struct zoneref are
*
* zonelist_zone() - Return the struct zone * for an entry in _zonerefs
* zonelist_zone_idx() - Return the index of the zone for an entry
* zonelist_node_idx() - Return the index of the node for an entry
*///zone分配方案
struct zonelist {
    struct zonelist_cache *zlcache_ptr;          // NULL or &zlcache
    struct zoneref _zonerefs[MAX_ZONES_PER_ZONELIST + 1];
#ifdef CONFIG_NUMA
    struct zonelist_cache zlcache;               // optional ...
#endif
};
代码中的英文注释很详细了

初始化

Start_kernel()->build_all_zonelists()

void build_all_zonelists(void)
{
    /*设置全局变量current_zonelist_order*/
    set_zonelist_order();

    if (system_state == SYSTEM_BOOTING) {
    /*对所有节点创建zonelists*/
        __build_all_zonelists(NULL);
    /*调试用*/
        mminit_verify_zonelist();
        cpuset_init_current_mems_allowed();
    } else {
        /* we have to stop all cpus to guarantee there is no user
           of zonelist */
        stop_machine(__build_all_zonelists, NULL, NULL);
        /* cpuset refresh routine should be here */
    }
    /*计算所有zone中可分配的页面数之和*/
    vm_total_pages = nr_free_pagecache_pages();
    /*
     * Disable grouping by mobility if the number of pages in the
     * system is too low to allow the mechanism to work. It would be
     * more accurate, but expensive to check per-zone. This check is
     * made on memory-hotadd so a system can start with mobility
     * disabled and enable it later
     */
    if (vm_total_pages < (pageblock_nr_pages * MIGRATE_TYPES))
        page_group_by_mobility_disabled = 1;
    else
        page_group_by_mobility_disabled = 0;

    printk("Built %i zonelists in %s order, mobility grouping %s. "
        "Total pages: %ld/n",
            nr_online_nodes,
            zonelist_order_name[current_zonelist_order],
            page_group_by_mobility_disabled ? "off" : "on",
            vm_total_pages);
#ifdef CONFIG_NUMA
    printk("Policy zone: %s/n", zone_names[policy_zone]);
#endif
}

/* return values int ....just for stop_machine() */
static int __build_all_zonelists(void *dummy)
{
    int nid;

#ifdef CONFIG_NUMA
    memset(node_load, 0, sizeof(node_load));
#endif
    for_each_online_node(nid) {
        pg_data_t *pgdat = NODE_DATA(nid);
    /*创建zonelists，这个数组用来在分配内存中坐回绕，循环访问*/
        build_zonelists(pgdat);
    /*在UMA中，这个仅仅是把相关的变量设置成了NULL*/
        build_zonelist_cache(pgdat);
    }
    return 0;
}

static void build_zonelists(pg_data_t *pgdat)
{
    int node, local_node;
    enum zone_type j;
    struct zonelist *zonelist;

    local_node = pgdat->node_id;

    zonelist = &pgdat->node_zonelists[0];
    /*将zone添加到zone链表中，这样，zone中page的
    分配等操作将依靠这个环形的链表；*/
    j = build_zonelists_node(pgdat, zonelist, 0, MAX_NR_ZONES - 1);

    /*
     * Now we build the zonelist so that it contains the zones
     * of all the other nodes.
     * We don't want to pressure a particular node, so when
     * building the zones for node N, we make sure that the
     * zones coming right after the local ones are those from
     * node N+1 (modulo N)
     *//*对其他在线的节点创建zonelist*/
    for (node = local_node + 1; node < MAX_NUMNODES; node++) {
        if (!node_online(node))
            continue;
        j = build_zonelists_node(NODE_DATA(node), zonelist, j,
                            MAX_NR_ZONES - 1);
    }
    for (node = 0; node < local_node; node++) {
        if (!node_online(node))
            continue;
        j = build_zonelists_node(NODE_DATA(node), zonelist, j,
                            MAX_NR_ZONES - 1);
    }

    zonelist->_zonerefs[j].zone = NULL;
    zonelist->_zonerefs[j].zone_idx = 0;
}

/*
* Builds allocation fallback zone lists.
*
* Add all populated zones of a node to the zonelist.
*/
static int build_zonelists_node(pg_data_t *pgdat, struct zonelist *zonelist,
                int nr_zones, enum zone_type zone_type)
{
    struct zone *zone;

    BUG_ON(zone_type >= MAX_NR_ZONES);
    zone_type++;

    do {
        zone_type--;
        zone = pgdat->node_zones + zone_type;
        if (populated_zone(zone)) {/*如果以页面为单位的管理区的总大小不为0*/
            zoneref_set_zone(zone,/*设置管理区链表，将相关信息加入*/
                &zonelist->_zonerefs[nr_zones++]);
            check_highest_zone(zone_type);
        }

    } while (zone_type);
    return nr_zones;
}
内存管理区初始化主要是借助于启动分配器和以初始化的e820全局变量。内存管理区初始化后相应的伙伴系统、slab机制等等就可以在此基础上建立了，在后面会一点一点总结

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