linux-kernel - Re: [PATCH 0/6] DISCONTIGMEM support for PPC32

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Date:   Thu, 22 Feb 2018 00:31:58 +0100
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        linuxppc-dev@...ts.ozlabs.org, Joel Stanley <joel@....id.au>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/6] DISCONTIGMEM support for PPC32

On Wed, Feb 21, 2018 at 04:02:25PM +0100, Christophe LEROY wrote:
[...]
> > > My question might me stupid, as I don't know PCC64 in deep, but when looking
> > > at page_is_ram() in arch/powerpc/mm/mem.c, I have the feeling the PPC64
> > > implements ram by blocks. Isn't it what you are trying to achieve ? Wouldn't
> > > it be feasible to map to what's done in PPC64 for PPC32 ?
> > 
> > Using page_is_ram in __ioremap_caller and the same memblock-based
> > approach that's used on PPC64 on PPC32 *should* work, but I think due to
> > the following line in initmem_init, it won't:
> > 
> > 	memblock_set_node(0, (phys_addr_t)ULLONG_MAX, &memblock.memory, 0);
> 
> Can't we just fix that ?

Turns out I was completely wrong about this. memblock_set_node as called
above only assigns all memory to node 0 and merges *adjacent* memblocks.
It doesn't merge the memblocks on the Wii, which are far apart.

So now I actually have a working patchset (coming soon), that's a good
deal shorter than this patchset, and hopefully won't break
CONFIG_HIGHMEM in the same way.

Thanks for your input! :)


Jonathan Neuschäfer

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