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

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Message-ID: <20160923143413.GM5008@twins.programming.kicks-ass.net>
Date:   Fri, 23 Sep 2016 16:34:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Babu Moger <babu.moger@...cle.com>
Cc:     mingo@...hat.com, akpm@...ux-foundation.org, keescook@...omium.org,
        dan.j.williams@...el.com, aryabinin@...tuozzo.com, tj@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Ajust lockdep static allocations

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.