[SOLVED] mdev tmpfs 10 megabyte max limit?

[Rob Landley]

On 05/09/2013 03:08:16 PM, Walter Dnes wrote:
> On Thu, May 09, 2013 at 12:26:34PM +0200, Harald Becker wrote
> > Hi Walter !
> >
> > > Yesterday, it started blowing up on me.  After painfull  
> debugging, I
> > > discovered that /dev/shm now only 10 megabytes.
> >
> > Did you change your kernel and or other system start information?
> >
> > tmpfs has a mount option to specify the maximum size. As /dev/shm is
> > usually for small shared memory regions (POSIX) it gets limited to
> > smaller size than 50% of available RAM.
> >
> > Try 'mount -oremount,size=100M /dev/shm' ... but this is all not
> > Busybox related.
> 
>   That was almost, but not quite, the correct answer.  More spelunking
> shows that there is no built-in limit for /dev/shm per se.  However,
> /dev/shm is mounted on top of /dev.
> And /etc/mtab showed...
> 
> mdev /dev tmpfs rw,nosuid,relatime,size=10240k,mode=755 0 0
> 
>   On a physical disk, you can't allocate a 1 gig mount on a 10  
> megabyte
> partition.  Similarly, you can't mount allocate a 1 gig /dev/shm on  
> top
> of a 10 meg /dev.  So the solution was to...
> 
> mount -oremount,size=500M /dev

If it really is a separate mount point, then that's a kernel bug. (If  
it's just a subdirectory, that's not. If they mounted a new /dev over  
/dev/shm then the undermount would be hidden...)

Do "df /dev" and "df /dev/shm" give different mount points?

Rob