本文介绍了在Linux系统中通过memblock设置系统保留物理内存的方法，包括三种不同的实现方式：通过修改内核源码预留内存、预留并释放内存创建空洞以及通过uboot参数指定可用内存范围。
在Linux系統中可以通過memblock來設置系統保留物理內存，防止這些內存被內存管理系統分配出去。
作者： 彭東林
郵箱： pengdonglin137@163.com
平臺
硬件平臺： TQ2440
Linux版本：Linux 3.14.45
說明
1. 在tq2440上，物理內存的起始地址是0x30000000，一共有64MB的內存，所以物理內存地址範圍是: 0x30000000 -> 0x33ffffff
2. 可以在uboot傳給kernel的參數bootargs中添加一個"memblock=debug"，這樣在Linux啓動的時候，會將設置memblock的信息打印出來
參考博文
http://bbs.chinaunix.net/thread-4143403-1-1.html
代碼調用
在Linux啓動的時候會調用machine相關的代碼定製部分系統保留內存，函數調用如下：
start_kernel
----> setup_arch
----> arm_memblock_init
----> mdesc->reserve()
所以我們可以修改machine相關的代碼，添加reserve函數的實現。
方法一
修改mach-tq2440.c如下：
1 diff --git a/arch/arm/mach-s3c24xx/mach-tq2440.c b/arch/arm/mach-s3c24xx/mach-tq2440.c 2 index f9679fb..da75db2 100644 3 --- a/arch/arm/mach-s3c24xx/mach-tq2440.c 4 +++ b/arch/arm/mach-s3c24xx/mach-tq2440.c 5 @@ -23,6 +23,7 @@ 6 #include <linux/platform_device.h> 7 #include <linux/io.h> 8 #include <linux/dm9000.h> 9 +#include <linux/memblock.h> 10 11 #include <asm/mach/arch.h> 12 #include <asm/mach/map.h> 13 @@ -503,11 +504,28 @@ static void __init tq2440_machine_init(void) 14 s3c_pm_init(); 15 } 16 17 +static void __init tq2440_reserve(void) { 18 + u32 paddr,size; 19 + 20 + printk("%s enter.\n", __func__); 21 + 22 + paddr = 0x32000000; 23 + size = 0x200000; 24 + 25 + if (memblock_reserve(paddr, size) < 0) { 26 + pr_err("failed to reserve DRAM - no memory\n"); 27 + return; 28 + } 29 + 30 + printk("reserve : reserve %dM mem\n", size>>20); 31 +} 32 + 33 MACHINE_START(TQ2440, "TQ2440") 34 /* Maintainer: Ben Dooks <ben-linux@fluff.org> */ 35 .atag_offset = 0x100, 36 37 .init_irq = s3c2440_init_irq, 38 + .reserve = tq2440_reserve, 39 .map_io = tq2440_map_io, 40 .init_machine = tq2440_machine_init, 41 .init_time = samsung_timer_init,
上面我們在0x32000000開始的地方保留了2MB的物理內存，然後調用memblock_reserve告訴系統。這個在系統的啓動信息中可以看到：
1 [ 0.000000] Machine: TQ2440 2 [ 0.000000] memblock_reserve: [0x00000030008200-0x0000003057fc03] flags 0x0 arm_memblock_init+0x4c/0x1bc 3 [ 0.000000] memblock_reserve: [0x00000030004000-0x00000030007fff] flags 0x0 arm_memblock_init+0x158/0x1bc 4 [ 0.000000] tq2440_reserve enter. 5 [ 0.000000] memblock_reserve: [0x00000032000000-0x000000321fffff] flags 0x0 tq2440_reserve+0x1c/0x50 6 [ 0.000000] reserve : reserve 2M mem 7 [ 0.000000] MEMBLOCK configuration: 8 [ 0.000000] memory size = 0x4000000 reserved size = 0x77ba04 9 [ 0.000000] memory.cnt = 0x1 10 [ 0.000000] memory[0x0] [0x00000030000000-0x00000033ffffff], 0x4000000 bytes flags: 0x0 11 [ 0.000000] reserved.cnt = 0x3 12 [ 0.000000] reserved[0x0] [0x00000030004000-0x00000030007fff], 0x4000 bytes flags: 0x0 13 [ 0.000000] reserved[0x1] [0x00000030008200-0x0000003057fc03], 0x577a04 bytes flags: 0x0 14 [ 0.000000] reserved[0x2] [0x00000032000000-0x000000321fffff], 0x200000 bytes flags: 0x0
上面的第5行和第14行就是我們自己設置的保留內存範圍信息。在Linux啓動後，在debugfs中也可以看到memblock的信息：
[root@TQ2440 /]# cat /sys/kernel/debug/memblock/memory 0: 0x30000000..0x33ffffff [root@TQ2440 /]# cat /sys/kernel/debug/memblock/reserved 0: 0x30004000..0x30007fff 1: 0x30008200..0x3057fc03 2: 0x32000000..0x321fffff 3: 0x33f60000..0x33ffbfff 4: 0x33ffc540..0x33ffc96b 5: 0x33ffc980..0x33ffc9f7 6: 0x33ffca00..0x33ffca03 7: 0x33ffca20..0x33ffca23 8: 0x33ffca40..0x33ffca43 9: 0x33ffca60..0x33ffca63 10: 0x33ffca80..0x33ffcad2 11: 0x33ffcae0..0x33ffcb32 12: 0x33ffcb40..0x33ffcb92 13: 0x33ffcba0..0x33ffcbbb 14: 0x33ffcbc0..0x33ffcdc7 15: 0x33ffcdd0..0x33ffffff
其中memory節點中存放的是可用的物理內存地址範圍，reserved表示已經分配出去的物理地址，第2行記錄的就是我們設置的。
既然添加了保留物理內存，那麼如何使用呢？下面我寫了一個簡單的內核模塊，使用我們添加的保留物理內存，下面是內核模塊的代碼：
1 #include <linux/module.h> 2 3 #define RESERVE_PHY 0x32000000 4 #define RESERVE_SIZE 0x200000 5 6 static char str[] = "pengdonglin137@163.com\n"; 7 8 static __init int reserve_demo_init(void) 9 { 10 memcpy(phys_to_virt(RESERVE_PHY), str, sizeof(str)); 11 12 printk("%s: virt: %p\n", __func__, phys_to_virt(RESERVE_PHY)); 13 14 return 0; 15 } 16 17 static __exit void reserve_demo_exit(void) 18 { 19 printk("%s: %s\n", __func__, (char *)phys_to_virt(RESERVE_PHY)); 20 } 21 22 module_init(reserve_demo_init); 23 module_exit(reserve_demo_exit); 24 MODULE_LICENSE("GPL");
可以看到，我們直接調用函數phys_to_virt將物理地址轉換成虛擬地址，然後直接向這個虛擬地址中寫入數據，在模塊卸載時再將內容打印出出來。
1 [root@TQ2440 /]# insmod nfs/demo.ko 2 [ 1417.153362] reserve_demo_init: virt: c2000000 3 [root@TQ2440 /]# 4 [root@TQ2440 /]# rmmod demo 5 [ 1420.986938] reserve_demo_exit: pengdonglin137@163.com 6 [ 1420.986938]
可以看到，第2行中得到物理地址0x32000000對應的虛擬地址是0xC2000000。在模塊卸載時打印出了我們之前寫入的內容。
這種方法使用與物理內存在Normal區域的情況。
方法二
修改mach-tq2440.c
1 diff --git a/arch/arm/mach-s3c24xx/mach-tq2440.c b/arch/arm/mach-s3c24xx/mach-tq2440.c 2 index f9679fb..345a868 100644 3 --- a/arch/arm/mach-s3c24xx/mach-tq2440.c 4 +++ b/arch/arm/mach-s3c24xx/mach-tq2440.c 5 @@ -23,6 +23,7 @@ 6 #include <linux/platform_device.h> 7 #include <linux/io.h> 8 #include <linux/dm9000.h> 9 +#include <linux/memblock.h> 10 11 #include <asm/mach/arch.h> 12 #include <asm/mach/map.h> 13 @@ -503,11 +504,31 @@ static void __init tq2440_machine_init(void) 14 s3c_pm_init(); 15 } 16 17 +static void __init tq2440_reserve(void) { 18 + u32 paddr,size; 19 + 20 + printk("%s enter.\n", __func__); 21 + 22 + paddr = 0x32000000; 23 + size = 0x200000; 24 + 25 + if (memblock_reserve(paddr, size) < 0) { 26 + pr_err("failed to reserve DRAM - no memory\n"); 27 + return; 28 + } 29 + 30 + memblock_free(paddr, size); 31 + memblock_remove(paddr, size); 32 + 33 + printk("reserve : reserve %dM mem\n", size>>20); 34 +} 35 + 36 MACHINE_START(TQ2440, "TQ2440") 37 /* Maintainer: Ben Dooks <ben-linux@fluff.org> */ 38 .atag_offset = 0x100, 39 40 .init_irq = s3c2440_init_irq, 41 + .reserve = tq2440_reserve, 42 .map_io = tq2440_map_io, 43 .init_machine = tq2440_machine_init, 44 .init_time = samsung_timer_init,
用新kernel啓動，在啓動信息中可以看到：
1 [ 0.000000] Machine: TQ2440 2 [ 0.000000] memblock_reserve: [0x00000030008200-0x0000003057fc03] flags 0x0 arm_memblock_init+0x4c/0x1bc 3 [ 0.000000] memblock_reserve: [0x00000030004000-0x00000030007fff] flags 0x0 arm_memblock_init+0x158/0x1bc 4 [ 0.000000] tq2440_reserve enter. 5 [ 0.000000] memblock_reserve: [0x00000032000000-0x000000321fffff] flags 0x0 tq2440_reserve+0x1c/0x68 6 [ 0.000000] memblock_free: [0x00000032000000-0x000000321fffff] tq2440_reserve+0x3c/0x68 7 [ 0.000000] reserve : reserve 2M mem 8 [ 0.000000] MEMBLOCK configuration: 9 [ 0.000000] memory size = 0x3e00000 reserved size = 0x57ba04 10 [ 0.000000] memory.cnt = 0x2 11 [ 0.000000] memory[0x0] [0x00000030000000-0x00000031ffffff], 0x2000000 bytes flags: 0x0 12 [ 0.000000] memory[0x1] [0x00000032200000-0x00000033ffffff], 0x1e00000 bytes flags: 0x0 13 [ 0.000000] reserved.cnt = 0x2 14 [ 0.000000] reserved[0x0] [0x00000030004000-0x00000030007fff], 0x4000 bytes flags: 0x0 15 [ 0.000000] reserved[0x1] [0x00000030008200-0x0000003057fc03], 0x577a04 bytes flags: 0x0
在kernel啓動後，在memory和reserved節點中：
[root@TQ2440 /]# cat /sys/kernel/debug/memblock/memory 0: 0x30000000..0x31ffffff 1: 0x32200000..0x33ffffff
可以看到，此時系統中有兩塊物理內存，但是這兩塊物理內存的地址之間不連續，中間有一個大小爲2MB的“洞”。此時在reserved節點看不到這部分內存。
[root@TQ2440 /]# cat /sys/kernel/debug/memblock/reserved 0: 0x30004000..0x30007fff 1: 0x30008200..0x3057fc03 2: 0x33f60000..0x33ffbfff 3: 0x33ffc520..0x33ffc94b 4: 0x33ffc960..0x33ffc9d7 5: 0x33ffc9e0..0x33ffc9e3 6: 0x33ffca00..0x33ffca03 7: 0x33ffca20..0x33ffca23 8: 0x33ffca40..0x33ffca43 9: 0x33ffca60..0x33ffcab2 10: 0x33ffcac0..0x33ffcb12 11: 0x33ffcb20..0x33ffcb72 12: 0x33ffcb80..0x33ffcb9b 13: 0x33ffcba0..0x33ffcbbb 14: 0x33ffcbc0..0x33ffcdc7 15: 0x33ffcdd0..0x33ffffff
此時在使用這部分保留內存時就不能直接使用了，需要申請，然後映射後才能使用，如下：
1 #include <linux/module.h> 2 #include <linux/ioport.h> 3 #include <linux/io.h> 4 5 #define RESERVE_PHY 0x32000000 6 #define RESERVE_SIZE 0x200000 7 8 static char str[] = "pengdonglin137@163.com\n"; 9 static void __iomem *addr; 10 11 static __init int reserve_demo_init(void) 12 { 13 14 if (!request_mem_region(RESERVE_PHY, RESERVE_SIZE, "my reserve")) 15 return -EBUSY; 16 17 addr = ioremap_nocache(RESERVE_PHY, RESERVE_SIZE); 18 memcpy(addr, str, sizeof(str)); 19 20 printk("%s: virt: %p\n", __func__, addr); 21 22 return 0; 23 } 24 25 static __exit void reserve_demo_exit(void) 26 { 27 printk("%s: %s\n", __func__, (char *)addr); 28 29 iounmap(addr); 30 release_mem_region(RESERVE_PHY, RESERVE_SIZE); 31 } 32 33 module_init(reserve_demo_init); 34 module_exit(reserve_demo_exit); 35 MODULE_LICENSE("GPL");
然後加載這個模塊，此時會向addr中寫入字符串，在卸載時再打印出來。log如下：
1 [root@TQ2440 /]# insmod nfs/demo.ko 2 [ 43.853848] reserve_demo_init: virt: c5000000 3 [root@TQ2440 /]# 4 [root@TQ2440 /]# rmmod demo 5 [ 49.247204] reserve_demo_exit: pengdonglin137@163.com 6 [ 49.247204] 7 [root@TQ2440 /]#
方法三
在uboot可以通過在bootargs中設置mem參數，告訴kernel可用的物理內存。
修改uboot傳給kernel的bootargs，如下：
setenv bootargs "memblock=debug noinitrd root=/dev/mtdblock2 init=/linuxrc console=ttySAC0,115200n8 mem=32M"
此時啓動Linux，啓動信息中可以看到：
[ 0.000000] memblock_reserve: [0x00000030008200-0x00000030589c83] flags 0x0 arm_memblock_init+0x5c/0x1d8 [ 0.000000] memblock_reserve: [0x00000030004000-0x00000030007fff] flags 0x0 arm_memblock_init+0x8c/0x1d8 [ 0.000000] MEMBLOCK configuration: [ 0.000000] memory size = 0x2000000 reserved size = 0x585a84 [ 0.000000] memory.cnt = 0x1 [ 0.000000] memory[0x0] [0x00000030000000-0x00000031ffffff], 0x2000000 bytes flags: 0x0 [ 0.000000] reserved.cnt = 0x2 [ 0.000000] reserved[0x0] [0x00000030004000-0x00000030007fff], 0x4000 bytes flags: 0x0 [ 0.000000] reserved[0x1] [0x00000030008200-0x00000030589c83], 0x581a84 bytes flags: 0x0 ... ... [ 0.000000] Memory: 26752K/32768K available (3912K kernel code, 214K rwdata, 1176K rodata, 155K init, 176K bss, 6016K reserved)
可以看到，此時Linux只知道有32MB的物理內存，而實際上板子上有64MB的物理內存。
可以看到memory和reserved節點的內容如下：
1 [root@TQ2440 /]# cat /d/memblock/memory 2 0: 0x30000000..0x31ffffff 3 [root@TQ2440 /]# 4 [root@TQ2440 /]# cat /d/memblock/reserved 5 0: 0x30004000..0x30007fff 6 1: 0x30008200..0x30589c83 7 2: 0x31fa6000..0x31ffbfff 8 3: 0x31ffc840..0x31ffca6b 9 4: 0x31ffca80..0x31ffcaf7 10 5: 0x31ffcb00..0x31ffcb03 11 6: 0x31ffcb20..0x31ffcb23 12 7: 0x31ffcb40..0x31ffcb43 13 8: 0x31ffcb60..0x31ffcb63 14 9: 0x31ffcb80..0x31ffcbda 15 10: 0x31ffcbe0..0x31ffcc3a 16 11: 0x31ffcc40..0x31ffcc9a 17 12: 0x31ffcca0..0x31ffccbb 18 13: 0x31ffccc0..0x31ffcdc3 19 14: 0x31ffcdd0..0x31ffffff
使用剩餘的物理內存，同樣需要先申請，再映射，然後再使用：
1 #include <linux/module.h> 2 #include <linux/ioport.h> 3 #include <linux/io.h> 4 5 #define RESERVE_PHY 0x32000000 6 #define RESERVE_SIZE 0x200000 7 8 static char str[] = "pengdonglin137@163.com\n"; 9 static void __iomem *addr; 10 11 static __init int reserve_demo_init(void) 12 { 13 14 if (!request_mem_region(RESERVE_PHY, RESERVE_SIZE, "my reserve")) 15 return -EBUSY; 16 17 addr = ioremap_nocache(RESERVE_PHY, RESERVE_SIZE); 18 memcpy(addr, str, sizeof(str)); 19 20 printk("%s: virt: %p\n", __func__, addr); 21 22 return 0; 23 } 24 25 static __exit void reserve_demo_exit(void) 26 { 27 printk("%s: %s\n", __func__, (char *)addr); 28 29 iounmap(addr); 30 release_mem_region(RESERVE_PHY, RESERVE_SIZE); 31 } 32 33 module_init(reserve_demo_init); 34 module_exit(reserve_demo_exit); 35 MODULE_LICENSE("GPL");
加載模塊，然後卸載，可以看到log：
1 root@TQ2440 /]# insmod /nfs/demo.ko 2 [ 266.998897] reserve_demo_init: virt: c3000000 3 [root@TQ2440 /]# 4 [root@TQ2440 /]# rmmod demo 5 [ 271.735731] reserve_demo_exit: pengdonglin137@163.com 6 [ 271.735731]
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