For review: NAND out of space patch.

[Jim Gettys]

Ah, I like this idea better than the previous I've heard; if we can
uninstall software or cleanup the journal with human intervention, that
would be good....  I'm nervous about automatic cleanup schemes....
                       - Jim


On Tue, 2008-07-22 at 13:20 -0400, Erik Garrison wrote:
> On Tue, Jul 22, 2008 at 12:53:37PM -0300, John Watlington wrote:
> > 
> > On Jul 22, 2008, at 12:06 PM, Chris Ball wrote:
> > 
> > > Hi,
> > >
> > >> Can you walk me through the exact steps that the user would
> > >> experience if this script was installed?
> > >
> > > They wouldn't see anything different, but Journal entries  
> > > corresponding
> > > to files we chose to delete wouldn't resume properly.
> > >
> > >> In terms of which files, I think the oldest (or maybe LRU as they
> > >> say in caches) would be better than the largest. Can we do that
> > >> (e.g. delete oldest then iterate until x MBs is free)?
> > >
> > > I disagree; I don't think we're filling up with small Write or Paint
> > > documents, my intuition is that we're filling up with recent large
> > > downloads and movies.  In the case where the problem is a huge  
> > > download
> > > the user just made, your scheme results in deleting *everything*.
> > >
> > > Since we disagree, maybe best to wait until we have some disk-full
> > > images back from the field so that we can see what used up all the
> > > space, before deciding the algorithm.
> > 
> > I'm getting three images right now.
> > 
> > One of the machines booted, but wouldn't allow any activities to launch
> > (which since you can't log in on vttys kinda locks down the machine).
> > But I did notice a large number of non-standard activities (e.g. Doom).
> 
> This sounds familiar.  I think several teachers from Uruguay have
> mentioned on the Sur list that their students love to download software
> and have filled up their storage space.  I'll try to find the reference.
> I have also heard the same from a contractor in Uruguay who has been
> involved in distribution (via #olpc-ayuda).
> 
> Today I am going to test a solution in which we union-mount a tmpfs over
> top of a full root filesystem (which is effectively read-only).  This
> should allow us to boot, but obviously any changes made to the tmpfs
> during the session will be lost.  Provided we can boot in this scheme,
> we should immediately open a dialogue which asks the user to select
> Activities to delete.
> 
> I think that such a 'recovery-mode' is ultimately the best we're going
> to do to help resolve this issue.  We must provide students a way to
> manage their systems, and to do so even in a NAND-full state, or the
> solution to NAND-full will continue to be centralized and costly.  If it
> is not something that we ship immediately to help resolve the issue in
> Uruguay, the current situation demonstrates that it is a worthwhile
> target for future releasese.
> 
> Erik
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-- 
Jim Gettys <jg at laptop.org>
One Laptop Per Child