Re: [linux-next:master 3778/4413] include/linux/mmzone.h:1749:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE

[WANG Xuerui <kernel@xen0n.name>]

On 2023/3/22 15:42, Mike Rapoport wrote:
> On Tue, Mar 21, 2023 at 10:59:36AM +0800, Huacai Chen wrote:
>> Hi, all,
>>
>> On Mon, Mar 20, 2023 at 11:56 PM Kirill A. Shutemov
>> <kirill@shutemov.name> wrote:
>>>
>>> On Mon, Mar 20, 2023 at 04:06:33PM +0800, kernel test robot wrote:
>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
>>>> head:   73f2c2a7e1d2b31fdd5faa6dfa151c437a6c0a5a
>>>> commit: af8daebdbc0833b8095767ccef7ddce55e9fdf32 [3778/4413] mm, treewide: redefine MAX_ORDER sanely
>>>> config: loongarch-buildonly-randconfig-r003-20230320 (https://download.01.org/0day-ci/archive/20230320/202303201615.Qfu18nWV-lkp@intel.com/config)
>>>> compiler: loongarch64-linux-gcc (GCC) 12.1.0
>>>> reproduce (this is a W=1 build):
>>>>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>>>          chmod +x ~/bin/make.cross
>>>>          # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=af8daebdbc0833b8095767ccef7ddce55e9fdf32
>>>>          git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>>>>          git fetch --no-tags linux-next master
>>>>          git checkout af8daebdbc0833b8095767ccef7ddce55e9fdf32
>>>>          # save the config file
>>>>          mkdir build_dir && cp config build_dir/.config
>>>>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch olddefconfig
>>>>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch prepare
>>>>
>>>> If you fix the issue, kindly add following tag where applicable
>>>> | Reported-by: kernel test robot <lkp@intel.com>
>>>> | Link: https://lore.kernel.org/oe-kbuild-all/202303201615.Qfu18nWV-lkp@intel.com/
>>>>
>>>> All errors (new ones prefixed by >>):
>>>>
>>>>     In file included from include/linux/gfp.h:7,
>>>>                      from include/linux/mm.h:7,
>>>>                      from arch/loongarch/kernel/asm-offsets.c:9:
>>>>>> include/linux/mmzone.h:1749:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE
>>>>      1749 | #error Allocator MAX_ORDER exceeds SECTION_SIZE
>>>>           |  ^~~~~
>>>
>>> +Loongarch folks.
>> LoongArch defines SECTION_SIZE_BITS as 29, so I think the upper limit
>> of ARCH_FORCE_MAX_ORDER should not be 63, MIPS is similar.
>   
> The ranges MIPS add LoongArch define for ARCH_FORCE_MAX_ORDER are insane.
> I'm going to drop them and leave ARCH_FORCE_MAX_ORDER an int with sane
> defaults.
> 
> As for this splat, in the .config above ARCH_FORCE_MAX_ORDER=14 and
> PAGE_SIZE=64k, so we end up with MAX_ORDER + PAGE_SHIFT being 30, that's
> larger than SECTION_SIZE.
> 
> AFAIK randconfig does not randomize integers, so it's unclear to me how
> ARCH_FORCE_MAX_ORDER got to 14.
> 

As far as I can see, arch/loongarch/Kconfig has the following lines:

 > config ARCH_FORCE_MAX_ORDER
 >         int "Maximum zone order"
 >         range 14 64 if PAGE_SIZE_64KB
 >         default "14" if PAGE_SIZE_64KB
 >         range 12 64 if PAGE_SIZE_16KB
 >         default "12" if PAGE_SIZE_16KB
 >         range 11 64
 >         default "11"

So the value 14 is because PAGE_SIZE_64KB is being set, which I 
confirmed to be the case with this particular run. And I believe the 
stanza is inherited from arch/mips.

Looking at other arches it seems a much smaller upper limit would be 
desirable. Even the lower limit of 14 could be lowered, e.g. 
arch/powerpc has "range 8 9 if PPC64 && PPC_64K_PAGES". Is that okay?

-- 
WANG "xen0n" Xuerui

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