dts中memreserve和reserved-memory的区别

心已赠人 2023-07-11 11:24 170阅读 0赞

Devicetree 提供了两种方式预留内存: reserved-memory和memreserve

memreserve示例

/memreserve/ 0x40000000 0x01000000

reserved-memory示例

reserved-memory {
            #address-cells = <1>;
            #size-cells = <1>;
            ranges;
     
            ipu_cma@90000000 {
                compatible = "shared-dma-pool";
                reg = <0x90000000 0x4000000>;
                reusable;
                status = "okay";
            };

**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

![Center][]

**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

/* 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

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);
            ...
    }
    
    /** 
     * 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

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  
  
原文链接：https://blog.csdn.net/kickxxx/article/details/54631535

[Center]: https://img-blog.csdn.net/20170120152706409?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQva2lja3h4eA==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center