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

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Message-Id: <20180507161801.2641b71f63158839b9c528f3@linux-foundation.org>
Date:   Mon, 7 May 2018 16:18:01 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     kbuild test robot <lkp@...el.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>, kbuild-all@...org,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, peterz@...radead.org,
        oleg@...hat.com, viro@...iv.linux.org.uk, mingo@...nel.org,
        paulmck@...ux.vnet.ibm.com, keescook@...omium.org, riel@...hat.com,
        tglx@...utronix.de, kirill.shutemov@...ux.intel.com,
        marcos.souza.org@...il.com, hoeun.ryu@...il.com,
        pasha.tatashin@...cle.com, gs051095@...il.com, dhowells@...hat.com,
        rppt@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Balbir Singh <balbir@...ux.vnet.ibm.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] memcg: Replace mm->owner with mm->memcg

On Sun, 6 May 2018 00:54:48 +0800 kbuild test robot <lkp@...el.com> 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?