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Subject: Re: [PATCH v1 05/12] mm/memory_hotplug: remove nid parameter from
 remove_memory() and friends
To:     Michael Ellerman <mpe@ellerman.id.au>, linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
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References: <20210607195430.48228-1-david@redhat.com>
 <20210607195430.48228-6-david@redhat.com> <87y2bkehky.fsf@mpe.ellerman.id.au>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <7463b3ed-07d3-7157-629d-a85a3ff558d6@redhat.com>
Date:   Tue, 8 Jun 2021 13:18:55 +0200
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On 08.06.21 13:11, Michael Ellerman wrote:
> David Hildenbrand <david@redhat.com> writes:
>> There is only a single user remaining. We can simply try to offline all
>> online nodes - which is fast, because we usually span pages and can skip
>> such nodes right away.
> 
> That makes me slightly nervous, because our big powerpc boxes tend to
> trip on these scaling issues before others.
> 
> But the spanned pages check is just:
> 
> void try_offline_node(int nid)
> {
> 	pg_data_t *pgdat = NODE_DATA(nid);
>          ...
> 	if (pgdat->node_spanned_pages)
> 		return;
> 
> So I guess that's pretty cheap, and it's only O(nodes), which should
> never get that big.

Exactly. And if it does turn out to be a problem, we can walk all memory 
blocks before removing them, collecting the nid(s).

-- 
Thanks,

David / dhildenb