Linux RAMFS grows. Does it also shrink?

Question

The RAMFS file system automatically grows as much needed and as long as there is avaiable memory.

Removing files from it makes it shrink or it remain at the same size?

Answer 1

It will shrink back down again, at least on my CentOS 6.5 (kernel 2.6.32) system. Here's a test:

# mount none /tmp/test -t ramfs
# cd /tmp/test
# free -om | sed -n 1,2p
             total       used       free     shared    buffers     cached
Mem:          1829        778       1051          0         53        365

So I start out with 1051MB free RAM. Next I create a 100MB file in my new ramfs filesystem, and check my free RAM afterwards:

# pv -Ss 100M /dev/zero > test1
 100MiB 0:00:00 [ 315MiB/s] [================================>] 100%
# free -om | sed -n 1,2p
             total       used       free     shared    buffers     cached
Mem:          1829        877        951          0         53        465

Now I have 951MB free. I create another 100MB file to be sure it's ramfs taking up the RAM and not something else my desktop session is running:

# pv -Ss 100M /dev/zero > test2
 100MiB 0:00:00 [ 313MiB/s] [================================>] 100%
# free -om | sed -n 1,2p
             total       used       free     shared    buffers     cached
Mem:          1829        977        851          0         53        565

Now I have 851MB free, so the RAM is definitely being used up by my temporary files.

Next I delete the files and check my free RAM:

# rm -f test1 test2
# free -om | sed -n 1,2p
             total       used       free     shared    buffers     cached
Mem:          1829        778       1051          0         53        365

I'm back to 1051MB free. So the unused RAM is returned to the system.