请教一下top命令看到内存后的疑惑，与％M的区别

想知道用了多少内存，然后top看了一下根据%M加了一下，应该不足5%吧，为啥说used 2.4g呢？新手入门，谢谢了~top结果如下，根据M排序了top - 21:21:10 up 29 days, 5:23, 2 users, load average: 1.00, 1.00, 1.00Tasks: 91 total, 1 running, 90 sleeping, 0 stopped, 0 zombieCpu(s): 0.0% us, 0.1% sy, 0.0% ni, 99.9% id, 0.0% wa, 0.0% hi, 0.0% siMem: 4150904k total, 2412964k used, 1737940k free, 145080k buffersSwap: 2031608k total, 0k used, 2031608k free, 1379820k cachedPID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3023 root 25 0 104m 91m 932 S 0 2.2 1:03.84 clamd 27960 mysql 16 0 138m 29m 5140 S 0 0.7 1:33.78 mysqld 18983 root 15 0 34564 27m 2144 S 0 0.7 29:34.31 ruby 31004 root 16 0 21780 8424 4276 S 0 0.2 0:00.02 httpd 31011 apache 16 0 22020 7984 3580 S 0 0.2 0:00.77 httpd 31010 apache 16 0 22008 7900 3484 S 0 0.2 0:00.87 httpd 31012 apache 16 0 22028 7900 3488 S 0 0.2 0:00.86 httpd 31009 apache 16 0 22016 7888 3480 S 0 0.2 0:00.67 httpd 31008 apache 16 0 22032 7884 3468 S 0 0.2 0:00.93 httpd 31007 apache 16 0 22020 7876 3460 S 0 0.2 0:00.94 httpd 31013 apache 16 0 22016 7876 3460 S 0 0.2 0:00.67 httpd 31014 apache 16 0 22008 7876 3464 S 0 0.2 0:00.83 httpd 19771 root 16 0 8876 6080 1548 S 0 0.1 6:12.24 hald 8469 root 16 0 7052 2272 1816 S 0 0.1 0:00.00 sshd 8365 root 16 0 6960 2260 1816 S 0 0.1 0:00.01 sshd 11066 postfix 16 0 6196 1728 1388 S 0 0.0 0:00.03 qmgr-----除了一些服务占用的内存空间外，系统会划出一部分空间出来做cache用，两者之和是楼主说说的2.4g吧。