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

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Date:   Fri, 23 Sep 2016 09:50:52 -0500
From:   Babu Moger <babu.moger@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 9/23/2016 9:34 AM, Peter Zijlstra wrote:
> 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.

     Correct, We can't boot with lockdep. Sorry I did not make that 
clear.  We have a limit on static size of the kernel.

>
> In any case, maybe invert this, add make it depend on CONFIG_BASE_SMALL,
> since this really only matters for really dinky systems.
      Sure. Will  use  CONFIG_BASE_SMALL and re-post the patches. Thanks
>