Memory leak using cp command?

Hi,

I'm using cp command to copy some files. After some copies, the system
became slow. 
I used the "free" command, and I noted that free memory was just 1 mb.

[root@eduardo /home]# dd if=/dev/zero of=./fileTest bs=1024 count=10000
10000+0 records in
10000+0 records out
dd if=/dev/zero of=./fileTest bs=1024 count=10000

[root@eduardo /home]# ls -ls
-rwxr-xr-x    1 root     root     10240000 Mar 23 12:03 fileTest
drwxr-xr-x    1 root     root         2048 Dec 14 17:07 plg

[root@eduardo /home]# free
              total         used         free       shared      buffers
  Mem:        58996        21084        37912            0           28
 Swap:            0            0            0
Total:        58996        21084        37912
[root@eduardo /home]# 
[root@eduardo /home]# cp fileTest /tmp/a
[root@eduardo /home]# free
              total         used         free       shared      buffers
  Mem:        58996        41284        17712            0           28
 Swap:            0            0            0
Total:        58996        41284        17712
[root@eduardo /home]# cp fileTest /tmp/b
[root@eduardo /home]# free
              total         used         free       shared      buffers
  Mem:        58996        51120         7876            0           28
 Swap:            0            0            0
Total:        58996        51120         7876
[root@eduardo /home]# cp fileTest /tmp/c
[root@eduardo /home]# free
              total         used         free       shared      buffers
  Mem:        58996        57452         1544            0           28
 Swap:            0            0            0
Total:        58996        57452         1544

It seems that the memory is allocated but not deallocated by the cp
command.
What could cause that?

Anyone have the same problem?

(Kernel is a custom compilation of 2.6.32-2 version)

Thanks in advance

Take a look at the output of the "mount" command. I guess you are using a
RAM filesystem (called 'tmpfs') mounted on tmp/

For example on my host here:
[...]
tmpfs on /tmp type tmpfs (rw,mode=1777,size=2G,nr_inodes=1k)
[...]

Hi Juergen,

On rcS file (/etc/init.d/rcS) there's four lines:
/bin/mount -t ramfs none /dev
/bin/mount -n -t tmpfs tmpfs /dev/shm
/bin/mount -n -t ramfs none /tmp
/bin/mount -n -t ramfs none /var

I read about tempfs and ramfs, and now I agree with you... this could be
the reason.
So, I tried to copy the same file to the same directory where the original
file was (/home/):
obs: the result of free command is resumed here

# free 
Total:        58996        34800        24196

# cp fileTest ./fileTest11
# free
Total:        58996        45180        13816

At this time, I copied it to /home dir (and / is mounted on nand flash).
Why ram is in use?

Then, I tried to remove:
# rm fileTest11

And for my surprise, the memory was deallocated.
# free
Total:        58996        34800        24196


Now, I don't understand why the memory was allocated and freed when the
file was deleted. I suppose that this file should be on disk (nand flash)
after each copy, and not on ram... or I'm wrong?

I'll read more about ramfs, tempfs and yaffs. On my system I'll need to do
some file copies (logs, updates and etc), and I'm afraid that the system
could become slow or hang when the memory usage is high.

Linux uses the unused parts of the memory as its filesystem cache ("don't
waste unused memory"). If you copy large files this will consume the
memory. But this filesystem cache also shrinks again when applications
request for more memory.

You can check this behaviour by using this command after you copy the file:
 
echo 3 > /proc/sys/vm/drop_caches

This will free all cache memory immediately.

Hi Juergen,
I see it now. Thanks for your help.
The system may be slow for other reasons (and I'll find out)...