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

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Message-ID: <e50f8127-3a87-92eb-d88a-72aa1557ffe7@csgroup.eu>
Date:   Wed, 31 Mar 2021 16:12:06 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        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



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 :)

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.

Christophe