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

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	Jordan Niethe <jniethe5@gmail.com>
Subject: Re: [PATCH] powerpc/8xx: Load modules closer to kernel text
Date: Wed, 31 Mar 2021 16:12:06 +0200	[thread overview]
Message-ID: <e50f8127-3a87-92eb-d88a-72aa1557ffe7@csgroup.eu> (raw)
In-Reply-To: <87czvf788t.fsf@mpe.ellerman.id.au>

Le 31/03/2021 à 15:39, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@csgroup.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