NAND out of space crash

[C. Scott Ananian]

On Mon, Jul 21, 2008 at 12:52 PM, Jim Gettys <jg at laptop.org> wrote:
> There are two issues here that we should be sure to not intertwingle:
>
> 1) whatever behavior Sugar may have when low/out of space, during
> operation, or at boot time.

A number of independent issues here:
 a) the initscripts should be sure to unfreeze the dcon if/when X
fails to start.  This ensures that the system is obviously recoverable
(you can recover by rebooting with the check key held down, but this
is not obvious!).
 b) sugar should, ideally, start even if flash is full.   It is
currently failing when writing to ~olpc/.boot_time or some such, and
crashing.
 c) once sugar starts, there should be a message indicating that the
NAND is critically full.
 d) trying to save new content to the journal should also give an
obvious message that the NAND is full.
 e) removing content from the journal should work even if NAND is full.

I think (a), (b), and (e) are critical for 8.2.  (c) is being handled
independently by Uruguay, and (c) and (d) should be targets for 9.1.

> 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.
 --scott

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