C写个吃内存的测试LINUX 系统可用内存持续减少的原因

C 内存测试

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

main( int argc, char ** argv )
{
char * pTest=0;
long iSize;
if( 2 == argc ){
iSize = atoi( argv[1] );
}
else{
printf("Usage: eatmem <size>\n";
return 1;
}
//        if( NULL != ( pTest = (char*) malloc( iSize*sizeof(char) )))
if( NULL != ( pTest = new char[ iSize ] ))
printf( "Eat memory %ld\n", iSize );
else
printf( "No such more memory!\n" );
while(1){
memset(pTest,0,iSize);
sleep(10);
};
}

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.