linux-kernel - Re: [PATCH v1 05/12] mm/memory_hotplug: remove nid parameter from remove

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Date:   Tue, 8 Jun 2021 13:18:55 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michael Ellerman <mpe@...erman.id.au>, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Marek Kedzierski <mkedzier@...hat.com>,
        Hui Zhu <teawater@...il.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        linux-acpi@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Scott Cheloha <cheloha@...ux.ibm.com>,
        Anton Blanchard <anton@...abs.org>,
        linuxppc-dev@...ts.ozlabs.org, nvdimm@...ts.linux.dev
Subject: Re: [PATCH v1 05/12] mm/memory_hotplug: remove nid parameter from
 remove_memory() and friends

On 08.06.21 13:11, Michael Ellerman wrote:
> David Hildenbrand <david@...hat.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