Linux内存活动区域其实就是全局变量e820中的内存块做了相关的检查和对其处理后的区域。在管理区初始化等地方有用到。

数据结构

struct node_active_region {
    unsigned long start_pfn;
    unsigned long end_pfn;
    int nid;
};

初始化

活动内存的初始化工作在setup_arch()->initmem_init()->e820_register_active_regions()中

/* Walk the e820 map and register active regions within a node */
void __init e820_register_active_regions(int nid, unsigned long start_pfn,
                     unsigned long last_pfn)
{
    unsigned long ei_startpfn;
    unsigned long ei_endpfn;
    int i;

    for (i = 0; i < e820.nr_map; i++)
        if (e820_find_active_region(&e820.map[i],/*从全局变量e820中查找活动区*/
                        start_pfn, last_pfn,
                        &ei_startpfn, &ei_endpfn))
            add_active_range(nid, ei_startpfn, ei_endpfn);/*加入活动区*/
}

/*
 * Finds an active region in the address range from start_pfn to last_pfn and
 * returns its range in ei_startpfn and ei_endpfn for the e820 entry.
 */
int __init e820_find_active_region(const struct e820entry *ei,
                  unsigned long start_pfn,
                  unsigned long last_pfn,
                  unsigned long *ei_startpfn,
                  unsigned long *ei_endpfn)
{
    u64 align = PAGE_SIZE;

    *ei_startpfn = round_up(ei->addr, align) >> PAGE_SHIFT;
    *ei_endpfn = round_down(ei->addr + ei->size, align) >> PAGE_SHIFT;

    /* Skip map entries smaller than a page */
    if (*ei_startpfn >= *ei_endpfn)
        return 0;

    /* Skip if map is outside the node */
    if (ei->type != E820_RAM || *ei_endpfn <= start_pfn ||
                    *ei_startpfn >= last_pfn)
        return 0;

    /* Check for overlaps */
    if (*ei_startpfn < start_pfn)
        *ei_startpfn = start_pfn;
    if (*ei_endpfn > last_pfn)
        *ei_endpfn = last_pfn;

    return 1;
}

/*添加活动区域，需要对原有的进行检查*/
void __init add_active_range(unsigned int nid, unsigned long start_pfn,
                        unsigned long end_pfn)
{
    int i;

    mminit_dprintk(MMINIT_TRACE, "memory_register",
            "Entering add_active_range(%d, %#lx, %#lx) "
            "%d entries of %d used\n",
            nid, start_pfn, end_pfn,
            nr_nodemap_entries, MAX_ACTIVE_REGIONS);
//not set macro
    mminit_validate_memmodel_limits(&start_pfn, &end_pfn);

    /* Merge with existing active regions if possible */
    for (i = 0; i < nr_nodemap_entries; i++) {
        if (early_node_map[i].nid != nid)
            continue;

        /* Skip if an existing region covers this new one */
        if (start_pfn >= early_node_map[i].start_pfn &&
                end_pfn <= early_node_map[i].end_pfn)
            return;

        /* Merge forward if suitable */
        if (start_pfn <= early_node_map[i].end_pfn &&
                end_pfn > early_node_map[i].end_pfn) {
            early_node_map[i].end_pfn = end_pfn;
            return;
        }

        /* Merge backward if suitable */
        if (start_pfn < early_node_map[i].end_pfn &&
                end_pfn >= early_node_map[i].start_pfn) {
            early_node_map[i].start_pfn = start_pfn;
            return;
        }
    }

    /* Check that early_node_map is large enough */
    if (i >= MAX_ACTIVE_REGIONS) {
        printk(KERN_CRIT "More than %d memory regions, truncating\n",
                            MAX_ACTIVE_REGIONS);
        return;
    }

    early_node_map[i].nid = nid;
    early_node_map[i].start_pfn = start_pfn;
    early_node_map[i].end_pfn = end_pfn;
    nr_nodemap_entries = i + 1;
}