[Pkg-sysvinit-devel] Bug#390184: Bug#390184: Bug#390184: /lib/init/rw uses 1.8 Gbytes for nothing

[Roger Leigh]

On Tue, Jan 20, 2009 at 07:42:29PM +0100, Petter Reinholdtsen wrote:
> [Henrique de Moraes Holschuh]
> > Limiting /lib/init/rw to 10MB or so would be a damn good hint to
> > anything using it that we don't want any abuse there...  I don't see
> > why we wouldn't want to do it.
> 
> The reason I did not put a limit on it, is that I have no idea which
> systems need to store data before /var/run/ is writable, and thus did
> not want to put a unwanted limit on the usage from the start.
> 
> I have no problem changing the default size.  Lets do that just after
> Lenny is released, to see if we break anything. :)

Is now a good time to revisit this?  Looking back at the previous
discussion:

- /dev/shm is for POSIX SHM and SEM (shared memory and semaphores)
- /lib/init/rw is for data which needs to be written before /var
  is mounted during system startup.  Unless one is modifying data
  created during system startup, there is no reason to use this
  filesystem after startup since /var exists for this purpose.

Given the constraint on /lib/init/rw, it really is aimed at
storing small amounts of datafiles/scripts generated on startup.
A limit of 10 MiB here is more than generous.

On my system there are 5 files totalling 699 bytes!  That's resolvconf
and mdadm.

Previously dosemu and UML were mentioned as users of /dev/shm which
should really not be doing so, and /lib/init/rw was suggested as a
potential place for them to move to.  I don't agree which this
position: neither place is suitable for storing their mmapped files.
If they are using shm_open and mmap, then /dev/shm is appropriate
(indeed, it's exactly where they will be placed in root of the POSIX
SHM namespace).  However, if they are simply mmapping chunks of data
from their own written files such as disk images, then this is not
a suitable use for either.  They have the option of using:
- /var (if they don't strictly need the potential benefits of
  a VM-backed filesystem)
- mmap with an anonymous mapping
- their own dedicated tmpfs mounted under e.g. /var for their own
  storage requirements.


Regards,
Roger

-- 
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