Linux如何防止内存冲突？-电子发烧友网

在聊这个话题之前，我们先回忆一下单片机系统中是如何分配内存的？如果没有bootloader，那硬件环境起来之后就直接进入主程序运行，如果有引导程序bootloader，那就需要设置好跳转地址，否则设置不对，系统就无法启动了。

那么对于linux系统来说，何尝不是这样呢？因为linux系统包含的文件比较多，启动也分几个阶段，每个阶段也都是通过跳转执行的。如何管理好内存是系统稳定运行的前提。

原生的uboot只能管理自己所在的内存块，无法管理整块空间。于是rk引入了bidram和sysmem，用于管理uboot之外的地址空间，RK平台就把系统所有内存通过sysmem + bidram + malloc管理起来了，防止出现内存冲突等问题。

bidram：管理u-boot、kernel阶段不可用、需要剔除的内存块，例如：ATF、OP-TEE 占用的空间；sysmem：管理kernel 可见、可用的内存块。例如：fdt、ramdisk、kernel、fastboot 占用的空间。

相关代码：

./lib/sysmem.c./lib/bidram.c./include/memblk.h./arch/arm/mach-rockchip/memblk.c

先来大概预览一下源文件吧：

intsysmem_init(void){  struct sysmem *sysmem = &plat_sysmem;  phys_addr_t mem_start;  phys_size_t mem_size;  int ret;
  lmb_init(&sysmem->lmb);  INIT_LIST_HEAD(&sysmem->allocated_head);  INIT_LIST_HEAD(&sysmem->kmem_resv_head);  sysmem->allocated_cnt = 0;  sysmem->kmem_resv_cnt = 0;
  if (gd->flags & GD_FLG_RELOC) {    sysmem->has_initr = true;  } else {    SYSMEM_I("initn");    sysmem->has_initf = true;  }
  /* Add all available system memory */#ifdef CONFIG_NR_DRAM_BANKS  int i;
  for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {    if (!gd->bd->bi_dram[i].size)      continue;          ret = sysmem_add(gd->bd->bi_dram[i].start,         gd->bd->bi_dram[i].size);    if (ret) {      SYSMEM_E("Failed to add sysmem from bi_dram[%d]n", i);      goto fail;    }  }#else  mem_start = env_get_bootm_low();  mem_size = env_get_bootm_size();  ret = sysmem_add(mem_start, mem_size);  if (ret) {    SYSMEM_E("Failed to add sysmem from bootm_low/sizen");    goto fail;  }#endif  /* Reserved for board */  ret = board_sysmem_reserve(sysmem);  if (ret) {    SYSMEM_E("Failed to reserve sysmem for boardn");    goto fail;  }
  /* Reserved for U-boot framework: 'reserve_xxx()' */  mem_start = gd->start_addr_sp;  mem_size = gd->ram_top - mem_start;  if (!sysmem_alloc_base(MEM_UBOOT, mem_start, mem_size)) {    SYSMEM_E("Failed to reserve sysmem for U-Boot frameworkn");    ret = -ENOMEM;    goto fail;  }    /* Reserved for U-Boot stack */  mem_start = gd->start_addr_sp - CONFIG_SYS_STACK_SIZE;  mem_size = CONFIG_SYS_STACK_SIZE;  if (!sysmem_alloc_base(MEM_STACK, mem_start, mem_size)) {    SYSMEM_E("Failed to reserve sysmem for stackn");    ret = -ENOMEM;    goto fail;}return0;fail:  if (ret && !(gd->flags & GD_FLG_RELOC)) {    sysmem_dump();    SYSMEM_W("Maybe malloc size %d MiB is too large?nn",       SIZE_MB(CONFIG_SYS_MALLOC_LEN));}  return ret;}

sysmem 内存信息表：

sysmem_dump_all:--------------------------------------------------------------------// <1> 这里是sysmem可管理的总内存容量，即bidram<3>之外的可用ddr容量，对kernel可见。memory.rgn[0].addr = 0x00200000 - 0x08400000 (size: 0x08200000)memory.rgn[1].addr = 0x0a200000 - 0x80000000 (size: 0x75e00000)memory.total = 0x7e000000 (2016 MiB. 0 KiB)--------------------------------------------------------------------// <2> 这里显示了各个固件alloc走的内存块信息allocated.rgn[0].name = "U-Boot".addr = 0x71dd6140 - 0x80000000 (size: 0x0e229ec0)allocated.rgn[1].name = "STACK"  // 表明栈溢出.addr = 0x71bd6140 - 0x71dd6140 (size: 0x00200000)allocated.rgn[2].name = "FDT".addr = 0x08300000 - 0x08316204 (size: 0x00016204)allocated.rgn[3].name = "KERNEL"  // 表明内存块溢出.addr = 0x00280000 - 0x014ce204 (size: 0x0124e204)allocated.rgn[4].name = "RAMDISK".addr = 0x0a200000 - 0x0a3e6804 (size: 0x001e6804)// <3> malloc_r/f的大小malloc_r: 192 MiB, malloc_f: 16 KiBallocated.total = 0x0f874acc (248 MiB. 466 KiB)--------------------------------------------------------------------// <4> 这里是核心算法对上述<2>进行的信息整理，显示被占用走的内存块信息LMB.reserved[0].addr = 0x00280000 - 0x014ce204 (size: 0x0124e204)LMB.reserved[1].addr = 0x08300000 - 0x08316204 (size: 0x00016204)LMB.reserved[2].addr = 0x0a200000 - 0x0a3e6804 (size: 0x001e6804)LMB.reserved[3].addr = 0x71bd6140 - 0x80000000 (size: 0x0e429ec0)reserved.core.total = 0x0f874acc (248 MiB. 466 KiB)--------------------------------------------------------------------

bidram 内存信息表：

bidram_dump_all:--------------------------------------------------------------------// <1> 这里显示了U-Boot从前级loader获取的ddr的总容量信息，一共有2GBmemory.rgn[0].addr = 0x00000000 - 0x80000000 (size: 0x80000000)memory.total = 0x80000000 (2048 MiB. 0 KiB)--------------------------------------------------------------------// <2> 这里显示了被预留起来的各固件内存信息，这些空间对kernel不可见reserved.rgn[0].name = "ATF".addr = 0x00000000 - 0x00100000 (size: 0x00100000)reserved.rgn[1].name = "SHM".addr = 0x00100000 - 0x00200000 (size: 0x00100000)reserved.rgn[2].name = "OP-TEE".addr = 0x08400000 - 0x0a200000 (size: 0x01e00000)reserved.total = 0x02000000 (32 MiB. 0 KiB)--------------------------------------------------------------------// <3> 这里是核心算法对上述<2>进行的预留信息整理，例如：会对相邻块进行合并LMB.reserved[0].addr = 0x00000000 - 0x00200000 (size: 0x00200000)LMB.reserved[1].addr = 0x08400000 - 0x0a200000 (size: 0x01e00000)reserved.core.total = 0x02000000 (32 MiB. 0 KiB)--------------------------------------------------------------------