[LTP] 答复: [PATCH] memcg_use_hierarchy_test.sh: skip setting use_hierarchy if not available

[Chen, Hanxiao]

Hi, Li

>发件人: Li Wang <liwang@redhat.com>
>发送时间: 2020年10月14日 14:28
>收件人: Xu, Yang <xuyang2018.jy@cn.fujitsu.com>; Chen, Hanxiao <chenhx.fnst@cn.fujitsu.com>
>抄送: LTP List <ltp@lists.linux.it>
>主题: Re: 答复: [LTP] [PATCH] memcg_use_hierarchy_test.sh: skip setting use_hierarchy if not available
>
>
>
>On Tue, Oct 13, 2020 at 11:19 AM Yang Xu <xuyang2018.jy@cn.fujitsu.com> wrote:
>Hi Hanxiao
>
>> Hi, Yang
>>
>>> -----閭欢鍘熶欢-----
>>> 涓婚: Re: [LTP] [PATCH] memcg_use_hierarchy_test.sh: skip setting
>>> use_hierarchy if not available
[snip]
>> The behavior above looks conflicting with https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt.
>Yes. Centos7 behavior is different from the documentation.
>>> So why not directly use /dev/memcg/memory.use_hierarchy value to judge in
>>> testcase after setting 0.
>> In setup_test from memcg_lib.sh, we actually did:
>>     mount -t cgroup -omemory memcg /dev/memcg
>> Then kernel will find a suitable cgroup root for us in cgroup1_mount.
>>
>> In this case, /sys/fs/cgroup/memory/ would be the good choice.
>> So it's equivalent to read memory.use_hierarchy from either side.
>I understand. Only a minor suggestion, please use tabs instead of spaces
>at the beginning of the line.
>
>
>This patch looks good to me,
>Acked-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
>
>@Li, I think this patch is ok, Do you have some comment about it?
>
>I'm ok to go with memory.use_hierarchy checking in the preconditioning phase.
>
>But how can you assert the default memory cgroup is mount at path: "/sys/fs/cgroup/memory", is there any possibility the default path mount at other places(for different distribution)?

https://github.com/torvalds/linux/blob/b5fc7a89e58bcc059a3d5e4db79c481fb437de59/kernel/cgroup/cgroup.c#L5768

WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));

So the default mount place should be /sys/fs/cgroup if distributions
did not modify these lines.

As the discussion above,
mount -t cgroup -omemory memcg /dev/memcg
kernel will find a suitable cgroup root for us.

How about reading /dev/memcg/memory.use_hierarchy as Yang recommended instead?

Regards,

-   Hanxiao

>--
>Regards,
>Li Wang


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