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Subject: Re: [PATCH 11/13] m68k/mm: make node data and node setup depend on
 CONFIG_DISCONTIGMEM
To:     Mike Rapoport <rppt@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Greg Ungerer <gerg@linux-m68k.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        Jonathan Corbet <corbet@lwn.net>,
        Matt Turner <mattst88@gmail.com>, Meelis Roos <mroos@linux.ee>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Russell King <linux@armlinux.org.uk>,
        Tony Luck <tony.luck@intel.com>,
        Vineet Gupta <vgupta@synopsys.com>,
        Will Deacon <will@kernel.org>,
        alpha <linux-alpha@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        "linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        Linux MM <linux-mm@kvack.org>,
        arcml <linux-snps-arc@lists.infradead.org>
References: <20201027112955.14157-1-rppt@kernel.org>
 <20201027112955.14157-12-rppt@kernel.org>
 <CAMuHMdU4r4CJ1kBu7gx1jkputjDn2S8Lqkj7RPfa3XUnM1QOFg@mail.gmail.com>
 <20201028111631.GF1428094@kernel.org>
From:   Michael Schmitz <schmitzmic@gmail.com>
Message-ID: <fd55643a-a17b-5a23-4c77-9e832c1e5128@gmail.com>
Date:   Thu, 29 Oct 2020 07:14:38 +1300
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Hi Mike,

On 29/10/20 12:16 AM, Mike Rapoport wrote:
> Hi Geert,
>
> On Wed, Oct 28, 2020 at 10:25:49AM +0100, Geert Uytterhoeven wrote:
>> Hi Mike,
>>
>> On Tue, Oct 27, 2020 at 12:31 PM Mike Rapoport <rppt@kernel.org> wrote:
>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>>
>>> The pg_data_t node structures and their initialization currently depends on
>>> !CONFIG_SINGLE_MEMORY_CHUNK. Since they are required only for DISCONTIGMEM
>>> make this dependency explicit and replace usage of
>>> CONFIG_SINGLE_MEMORY_CHUNK with CONFIG_DISCONTIGMEM where appropriate.
>>>
>>> The CONFIG_SINGLE_MEMORY_CHUNK was implicitly disabled on the ColdFire MMU
>>> variant, although it always presumed a single memory bank. As there is no
>>> actual need for DISCONTIGMEM in this case, make sure that ColdFire MMU
>>> systems set CONFIG_SINGLE_MEMORY_CHUNK to 'y'.
>>>
>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>> Thanks for your patch!
>>
>>> ---
>>>   arch/m68k/Kconfig.cpu           | 6 +++---
>>>   arch/m68k/include/asm/page_mm.h | 2 +-
>>>   arch/m68k/mm/init.c             | 4 ++--
>>>   3 files changed, 6 insertions(+), 6 deletions(-)
>> Is there any specific reason you didn't convert the checks for
>> CONFIG_SINGLE_MEMORY_CHUNK in arch/m68k/kernel/setup_mm.c
> In arch/m68k/kernel/setup_mm.c the CONFIG_SINGLE_MEMORY_CHUNK is needed
> for the case when a system has two banks, the kernel is loaded into the
> second bank and so the first bank cannot be used as normal memory. It
> does not matter what memory model will be used in this case.


That case used to be detected just fine at run time (by dint of the 
second memory chunk having an address below the first; the chunk the 
kernel resides in is always listed first), even without using 
CONFIG_SINGLE_MEMORY_CHUNK.

Unless you changed that behaviour (and I see nothing in your patch that 
would indicate that), this is still true.

Converting the check as Geert suggested, without also adding a test for 
out-of-order memory bank addresses, would implicitly treat DISCONTIGMEM 
as  SINGLE_MEMORY_CHUNK, regardless of bank ordering. I don't think that 
is what we really want?

Cheers,

     Michael


>
>> and arch/m68k/include/asm/virtconvert.h?
>   
> I remember I had build errors and troubles with include file
> dependencies if I changed it there, but I might be mistaken. I'll
> recheck again.
>
>> Gr{oetje,eeting}s,
>>
>>                          Geert
>>
>> -- 
>> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>>
>> In personal conversations with technical people, I call myself a hacker. But
>> when I'm talking to journalists I just say "programmer" or something like that.
>>                                  -- Linus Torvalds