linux-kernel - Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup in cpuset_init

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Message-ID: <3791e950-d997-23c0-07ff-909fd170d0a7@redhat.com>
Date:   Wed, 27 Apr 2022 10:33:04 -0400
From:   Waiman Long <longman@...hat.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Feng Tang <feng.tang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>, ying.huang@...el.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup
 in cpuset_init_smp()

On 4/27/22 09:53, Michal Koutný wrote:
> Hello.
>
> On Mon, Apr 25, 2022 at 11:55:05AM -0400, Waiman Long <longman@...hat.com> wrote:
>> smp_init() is called after the first two init functions.  So we don't
>> have a complete list of active cpus and memory nodes until later in
>> cpuset_init_smp() which is the right time to set up effective_cpus
>> and effective_mems.
> Yes.
>
> 	setup_arch
> 	  prefill_possible_map
> 	cpuset_init (1)
> 	cgroup_init
> 	  cpuset_bind (2a)
> 	...
> 	kernel_init
> 	  kernel_init_freeable
> 	    ...
> 	      cpuset_init_smp (3)
> 	...
> 	...
> 	cpuset_bind (2b)
>
>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 9390bfd9f1cd..6bd8f5ef40fe 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -3390,8 +3390,9 @@ static struct notifier_block cpuset_track_online_nodes_nb = {
>>    */
>>   void __init cpuset_init_smp(void)
>>   {
>> -	cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
>> -	top_cpuset.mems_allowed = node_states[N_MEMORY];
>> +	/*
>> +	 * cpus_allowd/mems_allowed will be properly set up in cpuset_bind().
>> +	 */
> IIUC, the comment should say
>
>> +	 * cpus_allowed/mems_allowed were (v2) or will be (v1) properly set up in cpuset_bind().
> (nit)
>
> Reviewed-by: Michal Koutný <mkoutny@...e.com>
>
Thanks for the review. I plan to post v3 with updated commit log and 
comment soon.

Cheers,
Longman