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Date:   Fri, 28 Oct 2022 19:29:57 +0800
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Subject: Re: [PATCH] cgroup: Simplify code in css_set_move_task
To:     =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
Cc:     tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20221020074701.84326-1-haifeng.xu@shopee.com>
 <20221027080558.GA23269@blackbody.suse.cz>
From:   Haifeng Xu <haifeng.xu@shopee.com>
In-Reply-To: <20221027080558.GA23269@blackbody.suse.cz>
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On 2022/10/27 16:05, Michal Koutný wrote:
> Hello.
> 
> On Thu, Oct 20, 2022 at 07:47:01AM +0000, "haifeng.xu" <haifeng.xu@shopee.com> wrote:
>> -	lockdep_assert_held(&css_set_lock);
>> +	if (!cset || cset is either getting the first task or losing the last(cset))
>> +		return;
> 
> 1) the guard should be css_set_populated() ^ populated (when unsetting
> the populated trait)
> 
> 2) I'd keep the lockdep_assert_held() after it anyway.
> 
> Also the commit message should explain what's the reason to move
> css_set_populated() after css_set_move_task().
> 
> 
> Thanks,
> Michal
Hi, Michal.

1) If calls 'css_set_update_populated' , the cset is either getting the
first task or losing the last. There is a need to update the populated
state of the cset only when 'css_set_populated' returns false.
In other words, the last has been deleted from from_cset and the first
hasn't been added to to_cset yet.

2) Thanks for your suggestion. I'll keep 'lockdep_assert_held'.

3) In order to update the populated state of to_cset the same way
from_cset does, 'css_set_update_populated' is also invoked during the
process of moving a task to to_cset.

Thanks,
Haifeng