linux-kernel - Re: [PATCH] powerpc/8xx: Load modules closer to kernel text

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Message-ID: <87ft0a1v5i.fsf@mpe.ellerman.id.au>
Date:   Thu, 01 Apr 2021 15:33:13 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Jordan Niethe <jniethe5@...il.com>
Subject: Re: [PATCH] powerpc/8xx: Load modules closer to kernel text

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> Le 31/03/2021 à 15:39, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>> On the 8xx, TASK_SIZE is 0x80000000. The space between TASK_SIZE and
>>> PAGE_OFFSET is not used.
>>>
>>> Use it to load modules in order to minimise the distance between
>>> kernel text and modules and avoid trampolines in modules to access
>>> kernel functions or other module functions.
>>>
>>> Define a 16Mbytes area for modules, that's more than enough.
>> 
>> 16MB seems kind of small.
>> 
>> At least on 64-bit we could potentially have hundreds of MBs of modules.
>> 
>
> Well, with a 16 MB kernel and 16 MB modules, my board is full :)

Heh.

> Even on the more recent board that has 128 MB, I don't expect more than a few MBs of modules in 
> addition to the kernel which is approx 8M.
>
> But ok, I'll do something more generic, though it will conflict with Jordan's series.

Don't feel you have to. You're the expert on 8xx, not me.

cheers