区别1:

二者在dtc编译时中处理的方法不同, reserved-memory做为device tree node解析到device-tree structure中; memreserve最终会加到dtb文件的memory reserve map,

见下图

区别2

二者在内核中的处理方式不同

1 memreserve处理流程

start_kernel - init/main.c

->setup_arch - arch/arm/kernel/setup.c

->arm_memblock_init - arch/arm/kernel/setup.c

->arm_dt_memblock_reserve - arch/arm/kernel/devtree.c

arm_dt_memblock_reserve实现如下

[cpp] view plain copy print ?

memblock_reserve(virt_to_phys(initial_boot_params),
be32_to_cpu(initial_boot_params->totalsize));
reserve_map = (( void *)initial_boot_params) +
be32_to_cpu(initial_boot_params->off_mem_rsvmap);
while (1) {
base = be64_to_cpup(reserve_map++);
size = be64_to_cpup(reserve_map++);
if (!size)
break ;
memblock_reserve(base, size);
}

    /* Reserve the dtb region */
    memblock_reserve(virt_to_phys(initial_boot_params),
             be32_to_cpu(initial_boot_params->totalsize));
     * Process the reserve map.  This will probably overlap the initrd
     * and dtb locations which are already reserved, but overlaping
     * doesn't hurt anything
    reserve_map = ((void*)initial_boot_params) +
            be32_to_cpu(initial_boot_params->off_mem_rsvmap);
    while (1) {
        base = be64_to_cpup(reserve_map++);
        size = be64_to_cpup(reserve_map++);
        if (!size)
            break;
        memblock_reserve(base, size);

initial_boot_params实际指向dtb文件在内存中的位置, 该地址还可以指向其他类型的启动参数

initial_boot_params头中的off_mem_rsvmap指向一系列的reserve memory(地址, 尺寸)空间, 对于dtb来说, 就是memory reserve map.

2 reserved-memory处理流程

start_kernel - init/main.c

->setup_arch - arch/arm/kernel/setup.c

->arm_memblock_init - arch/arm/kernel/setup.c

->early_init_fdt_scan_reserved_mem - arch/arm/mm/init.c

->__fdt_scan_reserved_mem, - drivers/of/fdt.c

->__reserved_mem_reserve_reg - drivers/of/fdt.c

->early_init_dt_reserve_memory_arch - drivers/of/fdt.c

->memblock_remove - mm/memblock.c

->memblock_reserve - mm/memblock.c

->fdt_init_reserved_mem

reserved-memory有一些可选参数, 比如no-map, 如果使用了no-map, 那么这段区域执行memblock_remove, 反之执行memblock_reserve.

在调用完memblock_reserve后,还会执行fdt_init_reserved_mem

[cpp] view plain copy print ?

void __init fdt_init_reserved_mem( void )
{
...
if (rmem->size == 0)
err = __reserved_mem_alloc_size(node, rmem->name,
&rmem->base, &rmem->size);
if (err == 0)
__reserved_mem_init_node(rmem);
...
}

void __init fdt_init_reserved_mem(void)
        if (rmem->size == 0)
            err = __reserved_mem_alloc_size(node, rmem->name,
                         &rmem->base, &rmem->size);
        if (err == 0)
            __reserved_mem_init_node(rmem);

[cpp] view plain copy print ?

static int __init __reserved_mem_init_node( struct reserved_mem *rmem)
{
...
for (i = __reservedmem_of_table; i < &__rmem_of_table_sentinel; i++) {
reservedmem_of_init_fn initfn = i->data;
const char *compat = i->compatible;
if (!of_flat_dt_is_compatible(rmem->fdt_node, compat))
continue ;
if (initfn(rmem) == 0) {
pr_info( "Reserved memory: initialized node %s, compatible id %s\n" ,
rmem->name, compat);
return 0;
}
}
return -ENOENT;
}

/** 
 * res_mem_init_node() - call region specific reserved memory init code
static int __init __reserved_mem_init_node(struct reserved_mem *rmem)
    for (i = __reservedmem_of_table; i < &__rmem_of_table_sentinel; i++) {
        reservedmem_of_init_fn initfn = i->data;
        const char *compat = i->compatible;
        if (!of_flat_dt_is_compatible(rmem->fdt_node, compat))
            continue;
        if (initfn(rmem) == 0) {
            pr_info("Reserved memory: initialized node %s, compatible id %s\n",
                rmem->name, compat);
            return 0;
    return -ENOENT;

如果reserved-memory下节点的compatible=<shared-dma-pool>, 则这块内存会被用来进行Contiguous Memory Allocator for dma

initfn对应drivers/base/dma-contiguous.c下的rmem_cma_setup以及drivers/base/dma-coherent.c中的rmem_dma_setup, 由于二者的compatible相同,所以前者优先.

rmem_cma_setup会对这块内存做初始化, 把这块区域加到cma_areas[cma_area_count]中

cma_areas保存着所有的CMA区域, 稍后core_init_reserved_areas会对这个数组进行处理

[cpp] view plain copy print ?

static int __init cma_init_reserved_areas( void )
{
int i;
for (i = 0; i < cma_area_count; i++) {
int ret = cma_activate_area(&cma_areas[i]);
if (ret)
return ret;
}
return 0;
}
core_initcall(cma_init_reserved_areas);

static int __init cma_init_reserved_areas(void)
    int i;
    for (i = 0; i < cma_area_count; i++) {
        int ret = cma_activate_area(&cma_areas[i]);
        if (ret)
            return ret;
    return 0;
core_initcall(cma_init_reserved_areas);

cma_activate_area把该cma area中的所有pages都改为MIGRATE_CMA, 并加到MIGRATE_CMA的free_list上.

区别3

由于二者的处理流程不同, 导致memreserve分配的内存, 无法再被操作系统使用; 而reserved-memory内存有可能进入系统CMA, 是否做为CMA, 依赖以下几个条件:

1. compatible 必须为shared-dma-pool

2. 没有定义no-map属性

3. 定义了resuable属性

版权声明：本文为CSDN博主「prike」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接： https://blog.csdn.net/prike/article/details/79524117