How to find size of RAM cache use for ramfs, tmpfs

I'm wondering if there is any way to specify the size of RAM cache used to store ramfs, tmpfs?

When I look at /proc/, I can't find anything about ramfs size.

Solution 1:

From http://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt:

Further on you can check the actual RAM+swap use of a tmpfs instance with df(1) and du(1).

So simply use df or du (you can also use them for ramfs):

$ df | grep tmpfs
tmpfs             205032      1136    203896   1% /run

so 1136 KB is in use.

$ sudo du -s /run
[sudo] password for jaume: 
1416    /run

so 1416 KB is in use.

Thats's interesting... df and du report different sizes. What is happening here and which one is right?

/run has a subfolder called /run/shm, which is itself a separate tmpfs filesytem (although shown as none):

$ df | grep run
tmpfs             205032      1136    203896   1% /run
none                5120         0      5120   0% /run/lock
none              512572       280    512292   1% /run/shm

Adding both amounts you get the size reported by du:

$ expr 1136 + 280
1416

So the whole story is that 2 tmpfs filesystems use 1416 KB.

(Here's another reason why du and df outputs may differ.)