tmpfs size restriction

[Ira W. Snyder]

On Wed, Apr 20, 2011 at 09:21:00PM +0200, Schwarz,Andre wrote:
> Hi,
> 
> I'm facing an issue with tmpfs mounts on PowerPC (mpc83xx specifically).
> 
> After "mount -t tmpfs tmpfs /tmp -o size=16m" I can fill the machine's mem
> (512MiB) until oom becomes active.
> 
> I can't see this on any other machine (x86/ARM) I have access to.
> There's always a "no space left on device" message as soon as size specified is
> reached ...
> 
> kernel versions available are v2.6.26.27 and v2.6.34.7 showing the same
> behaviour.
> 
> I'd expect the kernel to limit available tmpfs size to 50% of physical memory
> anyway.
> 
> Any ideas what might be wrong ?
> 

For what it is worth, I tried this on an 8349EA board, using 2.6.38rc8.
It behaved exactly as I would expect. A short log is below. Maybe your
mount command parses options differently on the powerpc machine? Try it
with the mount options before the mount points?

iws at carmaboard7 ~ $ mkdir mnt
mkdir: cannot create directory `mnt': File exists
iws at carmaboard7 ~ $ ls mnt/
iws at carmaboard7 ~ $ sudo mount -t tmpfs -o size=16m,users none mnt
iws at carmaboard7 ~ $ ls mnt/
iws at carmaboard7 ~ $ mount | grep mnt
none on /home/iws/mnt type tmpfs (rw,nosuid,nodev,noexec,relatime,size=16384k)
iws at carmaboard7 ~ $ cd ^C
iws at carmaboard7 ~ $ dd if=/dev/zero of=mnt/file.bin bs=1M count=18
dd: writing `mnt/file.bin': No space left on device
16+0 records in
15+0 records out
16760832 bytes (17 MB) copied, 0.313836 s, 53.4 MB/s
iws at carmaboard7 ~ $ du -b mnt/file.bin 
16760832        mnt/file.bin
iws at carmaboard7 ~ $ df -h mnt
Filesystem            Size  Used Avail Use% Mounted on
none                   16M     -     -   -  /home/iws/mnt
iws at carmaboard7 ~ $ uname -a
Linux carmaboard7.correlator.pvt 2.6.38-rc8-00028-g24d6894 #1 Tue Mar 8 09:48:15 PST 2011 ppc e300c1 GNU/Linux
iws at carmaboard7 ~ $ cat /proc/cpuinfo 
processor       : 0
cpu             : e300c1
clock           : 533.333328MHz
revision        : 3.1 (pvr 8083 0031)
bogomips        : 133.29
timebase        : 66646782
platform        : MPC834x MDS
model           : CARMA
Memory          : 256 MB

Hope it helps,
Ira