Re: [PATCH] memcg: Replace mm->owner with mm->memcg

[Andrew Morton]

On Sun, 6 May 2018 00:54:48 +0800 kbuild test robot <lkp@xxxxxxxxx> wrote:

> Hi Eric,
> 
> Thank you for the patch! Yet something to improve:
> 
> [auto build test ERROR on linus/master]
> [also build test ERROR on v4.17-rc3]
> [cannot apply to next-20180504]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Eric-W-Biederman/memcg-Replace-mm-owner-with-mm-memcg/20180503-120054
> config: xtensa-nommu_kc705_defconfig (attached as .config)
> compiler: xtensa-de212-elf-gcc (crosstool-NG crosstool-ng-1.23.0-307-g452ee331) 7.3.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=xtensa 
> 
> All errors (new ones prefixed by >>):
> 
>    kernel/fork.o: In function `sighand_ctor':
> >> fork.c:(.text+0x3b0): undefined reference to `mm_update_memcg'
>    kernel/fork.o: In function `mmdrop_async':
>    fork.c:(.text+0x43a): undefined reference to `mm_update_memcg'
>    kernel/fork.o: In function `set_task_stack_end_magic':
>    fork.c:(.text+0x752): undefined reference to `mm_update_memcg'

Due to the combination of CONFIG_MMU=n and CONFIG_MEMCG=y. 
mm/memcontrol.c's mm_update_memcg() depends upon CONFIG_MMU=y.

Is this a valid conbination?  Do we actually support (and test!) memcg
on nommu systems?