NAND out of space crash

[Jim Gettys]

On Mon, 2008-07-21 at 09:51 -0700, Deepak Saxena wrote:
> On Jul 21 2008, at 13:39, C. Scott Ananian was caught saying:
> > > 2) JFFS2's behavior when the file system is almost full.  When it gets
> > > almost full, it can spend all its time trying to garbage collect, and
> > > you can lose completely (the system sort of gets the "slows", and grinds
> > > to a halt).
> > >
> > > As to 2), there are patches done by Nokia (deployed on the N800 and
> > > similar devices) that reserve some extra space and report out of space
> > > before the system "gets the slows".  These are in Dave's incoming queue
> > > to merge into JFFS2 the last I heard.  I don't know if he's merged them.
> > 
> > These are less critical, IMO.  I have filled up NAND, and "the slows"
> > are not debilitating.  The issues above are. We should encourage Dave
> > to fix this issue and the other known JFFS2 bugs (trac #6480, for
> > instance)  -- or get dsaxena to do so -- for 9.1.
> 
> #6480 is fixed as of yesterday, should be in next joyride.
> 
> I'll be re-doing Nokia's patches so that they go upstream if we still want
> them after 8.2 is out; however, I don't think the approach used by them actually 
> helps us.  We already have a very limited amount of storage space and reserving 
> space for the root user just reduces what the end user can actually use.

IIRC, the issue is the GC runs more and more often the closer to full
you run.  By reserving some space, you avoid the performance cliff.

Since we expect to be running nearly full most of the time, it would
seem to me avoiding this cliff is important.

> 
> I think analyzing performance of non-JFFS2 file systems and picking
> a replacement should be a high-priority item for 9.1 update.

No argument here....
                          - Jim

> 
> ~Deepak
> 
-- 
Jim Gettys <jg at laptop.org>
One Laptop Per Child