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

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Message-ID: <20160923201756.GP5008@twins.programming.kicks-ass.net>
Date:   Fri, 23 Sep 2016 22:17:56 +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, Rob Gardner <rob.gardner@...cle.com>,
        davem@...emloft.net
Subject: Re: [PATCH 0/2] Ajust lockdep static allocations

On Fri, Sep 23, 2016 at 02:57:39PM -0500, Babu Moger wrote:

>  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. 

*sigh*, why didn't you start with that :/

> 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.

OK, so double check BASE_SMALL doesn't imply other things you cannot
live with, Sparc64 isn't a dinky system. If BASE_SMALL works for you
then good, otherwise do a PROVE_LOCKING_SMALL symbol that is not user
selectable and have SPARC select that. Use the invisible Help for that
symbol to explain all this again.

>  CCing David Miller and Rob Gardner. They might be able to explain
>  more if you have any more questions.

Nah, I think I remember enough of how the Sparc MMU works to see reason.