linux-kernel - Re: [PATCH 03/10] mm/migrate: update node demotion order during on hotplug events

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Date:   Tue, 9 Mar 2021 14:07:44 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yang Shi <shy828301@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>,
        Huang Ying <ying.huang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH 03/10] mm/migrate: update node demotion order during on
 hotplug events

On 3/8/21 4:03 PM, Yang Shi wrote:
>> +static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
>> +                                                unsigned long action, void *arg)
>> +{
>> +       switch (action) {
>> +       case MEM_GOING_OFFLINE:
>> +               /*
>> +                * Make sure there are not transient states where
>> +                * an offline node is a migration target.  This
>> +                * will leave migration disabled until the offline
>> +                * completes and the MEM_OFFLINE case below runs.
>> +                */
>> +               disable_all_migrate_targets();
>> +
>> +               /*
>> +                * Ensure the disable operation is globally visible.
>> +                * This avoids readers ever being able to
>> +                * simultaneously observe the old (pre-hotplug) and
>> +                * new (post-hotplug) migration targets.
>> +                */
>> +               synchronize_rcu();
> It seems disable_all_migrate_targets() already has synchronize_rcu()
> called. We don't need to call it twice. Otherwise, it looks good to
> me. Reviewed-by: Yang Shi <shy828301@...il.com>

Thanks for noticing that.  I've fixed it up.