rv1126 CMA内存管理机制

1 CMA概述

CMA的全称叫做contiguous memory allocator，它是为了便于进行连续物理内存申请的一块区域，一般我们把这块区域定义为reserved-memory。

2 CMA空间大小修改方式

修改CMA空间大小方法，例如：由原来的8M修改为64M：

1.CMA默认空间大小是在内核kernel里面定义的，打开menuconfig看到如下：

将Size in Mega Bytes的值由8改成64，这个值的单位是1MiB，改之后如下：

也就是相当于如下修改：

diff --git a/arch/arm/configs/rv1126_firefly_defconfig b/arch/arm/configs/rv1126_firefly_defconfig
index bb6e0678e380..cfd9ce69b0a9 100644
--- a/arch/arm/configs/rv1126_firefly_defconfig
+++ b/arch/arm/configs/rv1126_firefly_defconfig
@@ -98,7 +98,7 @@ CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y
 # CONFIG_ALLOW_DEV_COREDUMP is not set
 CONFIG_DMA_CMA=y
-CONFIG_CMA_SIZE_MBYTES=8
+CONFIG_CMA_SIZE_MBYTES=64

2.修改内核dtsi

diff --git a/arch/arm/boot/dts/rv1126.dtsi b/arch/arm/boot/dts/rv1126.dtsi
index 03c9b51538db..e4a11929f83f 100644
--- a/arch/arm/boot/dts/rv1126.dtsi
+++ b/arch/arm/boot/dts/rv1126.dtsi
@@ -374,7 +374,7 @@
                        compatible = "shared-dma-pool";
                        inactive;
                        reusable;
-                       size = <0x800000>;
+                       size = <0x4000000>;
                        linux,cma-default;
                };

修改之后，重新编译内核并烧录到板子上测试，注意：上面的配置文件和dtsi文件要根据自己板子的配置来定，里面修改的配置项名是一样的。

3查看CMA空间大小

通过开机log可以查看实际分配的CMA空间大小：

[root@RV1126_RV1109:/]# dmesg|grep -i reserve
[    0.000000] Reserved memory: created CMA memory pool at 0x39c00000, size 64 MiB
[    0.000000] OF: reserved mem: initialized node linux,cma, compatible id shared-dma-pool
[    0.000000] Reserved memory: created CMA memory pool at 0x29c00000, size 256 MiB
[    0.000000] OF: reserved mem: initialized node isp, compatible id shared-dma-pool
[    0.000000]   Normal zone: 0 pages reserved
[    0.000000] Memory: 681408K/1046240K available (10240K kernel code, 426K rwdata, 2644K rodata, 1024K init, 956K bss, 37152K reserved, 327680K cma-reserved, 0K highmem)
[    0.057514] hw-breakpoint: found 5 (+1 reserved) breakpoint and 4 watchpoint registers.
[    0.481906] rkcifhw ffae0000.rkcif: assigned reserved memory node isp
[    0.488660] rkisp_hw ffb50000.rkisp: assigned reserved memory node isp
[root@RV1126_RV1109:/]#

从log中第一条可以看出，CMA空间大小已经变为64MB。