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

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Message-ID: <fb01e1aa-bae4-432b-2d1a-7e0b20d04879@oracle.com>
Date:   Fri, 23 Sep 2016 14:57:39 -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, Rob Gardner <rob.gardner@...cle.com>,
        davem@...emloft.net
Subject: Re: [PATCH 0/2] Ajust lockdep static allocations

On 9/23/2016 10:40 AM, Peter Zijlstra wrote:
> On Fri, Sep 23, 2016 at 10:15:46AM -0500, Babu Moger wrote:
>
>>>>      Correct, We can't boot with lockdep. Sorry I did not make that clear.
>>>> We have a limit on static size of the kernel.
>>> This stuff should be in .bss not .data. It should not affect the static
>>> size at all. Or am I misunderstanding things?
>>   Here it is.
>> $ ./scripts/bloat-o-meter vmlinux.lockdep.small vmlinux.lockdep.big
> What does bloat-o-meter have to do with things? The static image size is
> not dependent on .bss, right?

  Peter,
  We checked again. Yes, It goes in .bss section. But in sparc we have 
to fit .text, .data,
  .bss in 7 permanent TLBs(that is totally 28MB). It was fine so far.  
But the commit
  1413c0389333 ("lockdep: Increase static allocations") added extra 4MB 
which makes
  it go beyond 28MB. That is causing system boot up problems in sparc. 
Yes. We know it.
  This is a limitation. Changing this limit in our hardware is a much 
bigger change which
  we cannot address right away. So, we are trying to come up with a 
solution which can
  work for all. I will re-post the patches with  CONFIG_BASE_SMALL 
option if there is no
  objections.

  CCing David Miller and Rob Gardner. They might be able to explain more 
if you
  have any more questions. Here is the discussion thread if you guys 
want to look at history.
  https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1237642.html