linux-kernel - Re: [PATCH] cgroup: wait for css offline when rmdir

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Date:   Tue, 31 May 2022 11:49:53 +0800
From:   Hongchen Zhang <zhanghongchen@...ngson.cn>
To:     Tejun Heo <tj@...nel.org>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: wait for css offline when rmdir

On 2022/5/31 上午9:01, Tejun Heo wrote:
> Hello,
> 
> On Mon, May 30, 2022 at 09:53:51AM +0800, Hongchen Zhang wrote:
>>    When I test the LTP's memcg_test_3 testcase at 8 Node server,I get the
>> -ENOMEM error,which caused by no avaliable idr found in mem_cgroup_idr.
>> the reason is the use of idr in mem_cgroup_idr is too fast than the free.In
>> the specific case,the idr is used and freed cyclically,so when we rmdir one
>> cgroup dir, we can synchronize the idr free through wating for the memcg css
>> offlined,and then we can use it the next cycle.
> 
> This is a micro benchmark specific problem and it doesn't make sense to
> change the overall behavior for this as the suggested change is neither
> desirable or logical. Maybe you can just incur the delay only after idr
> allocation fails and then retry?
> 
> Thanks.
> 
Hi Tejun,

Yes, the problem would disappear when add some reasonable delay. But I 
think if we can increase the MEM_CGROUP_ID_MAX to INT_MAX.Thus the 
-ENOMEM error would be never occured,even if the system is out of memory.

Thanks.