C写个吃内存的测试LINUX 系统可用内存持续减少的原因

2022-04-04 23:37:19

C 内存测试

01

#include
 <stdio.h>

02

#include
 <stdlib.h>

03

#include
 <unistd.h>

04

#include
 <string.h>

05

06

main( int argc, char **
 argv )

07

{

08

        char *
 pTest=0;

09

        long iSize;

10

        if(
 2 == argc ){

11

                iSize
 = atoi(
 argv[1] );

12

        }

13

        else{

14

                printf("Usage:
 eatmem <size>\n";

15

                return 1;

16

        }

17

//       
 if( NULL != ( pTest = (char*) malloc( iSize*sizeof(char) )))

18

        if(
 NULL != ( pTest = new char[
 iSize ] ))

19

                printf( "Eat
 memory %ld\n",
 iSize );

20

        else

21

                printf( "No
 such more memory!\n" );

22

        while(1){

23

                memset(pTest,0,iSize);

24

                sleep(10);

25

        };

26

}

先查看系统的空闲内存 , 约 1.8G
# free
         total    used    free    shared buffers    cached
Mem:    2061652    194896 1866756       0    13872    23648
-/+ buffers/cache:    157376 1904276
Swap:    4096312    141040 3955272

运行 eatmem 这个程序, 吃掉500M
./eatmem 500000000 &

再看系统的空闲内存, 少了500M 左右.
# free
         total    used    free    shared buffers    cached
Mem:    2061652    684476 1377176       0    14024    23648
-/+ buffers/cache:    646804 1414848
Swap:    4096312    141036 3955276

退出eatmem 再看, 内存几乎都回来了.
[root@l149 root]# free
         total    used    free    shared buffers    cached
Mem:    2061652    195600 1866052       0    14064    23648
-/+ buffers/cache:    157888 1903764
Swap:    4096312    141036 3955276

又做了一下试验....写个2G 的文件试试...

[root@l149 root]# free
         total    used    free    shared buffers    cached
Mem:    2061652    197080 1864572       0    14276    23648
-/+ buffers/cache:    159156 1902496
Swap:    4096312    141036 3955276
[root@l149 root]# dd if=/dev/zero of=2000M.file bs=10485760 count=200
200+0 records in
200+0 records out
[root@l149 root]# free
         total    used    free    shared buffers    cached
Mem:    2061652 2043584    18068       0    14332 1874308
-/+ buffers/cache:    154944 1906708
Swap:    4096312    141036 3955276
嘿嘿, 一写完文件, Free memory 就没有了.

有趣的是, 把这个文件一删除, Free memory 就又回来了.

码农公寓

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