Re: [PATCH 0/2] Ajust lockdep static allocations

[Peter Zijlstra]

On Fri, Sep 23, 2016 at 09:04:42AM -0500, Babu Moger wrote:
> On 9/23/2016 2:12 AM, Peter Zijlstra wrote:
> >On Thu, Sep 22, 2016 at 11:43:34AM -0700, Babu Moger wrote:
> >>These patches adjust the static allocations for lockdep
> >>data structures used for debugging locking correctness. The current
> >>code reserves about 4MB extra space for these data structures. Most
> >>of the configurations do not need these many data structures. While
> >>testing, I have not seen it go beyond 20% of already reserved entries.
> >>
> >>$grep "lock-classes" /proc/lockdep_stats
> >>	lock-classes:                          1560 [max: 8191]
> >>
> >>Reserving even more space seems unreasonable. So, keeping the default
> >>entries small as before the Commit 1413c0389333 ("lockdep: Increase static
> >>allocations"). Added new CONFIG_PROVE_LOCKING_PLUS in case someone
> >>needs more entries to debug their large configuration.
> >Why make this more complicated? There's absolutely no upside to this
> >change as far as I can see.
> Peter, What do you mean?  

I mean I see no point to the patches you send.

> Revert the commit 1413c038933? 

Nah, why would I?

> Right now, I cannot boot my setup after enabling lockdep. How do you
> think we can handle this?

Why can't you boot? You have that little memories? 4MB doesn't seem like
a worthwhile amount of memory.

Also, you didn't say.  This seems a somewhat crucial point.

In any case, maybe invert this, add make it depend on CONFIG_BASE_SMALL,
since this really only matters for really dinky systems.