linux-kernel - Re: [PATCH 2/6] mm: handle uninitialized numa nodes gracefully

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Date:   Fri, 4 Feb 2022 14:54:07 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Mike Rapoport <rppt@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Alexey Makhalov <amakhalov@...are.com>,
        Dennis Zhou <dennis@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Oscar Salvador <osalvador@...e.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Nico Pache <npache@...hat.com>,
        Rafael Aquini <raquini@...hat.com>
Subject: Re: [PATCH 2/6] mm: handle uninitialized numa nodes gracefully

On Thu, 3 Feb 2022 09:39:32 +0100 Michal Hocko <mhocko@...e.com> wrote:

> > I shuffled the words a bit, maybe this sounds better not only to me :)
> > 
> > /*
> >  * We do not want to confuse userspace by sysfs files/directories for node
> >  * without any memory attached to it, so this node is not marked as
> >  * N_MEMORY and not marked online so that topology_init() won't create
> >  * sysfs hierarchy for this node.  The pgdat will get fully initialized by
> >  * hotadd_init_pgdat() when memory is hotpluged into this node
> >  */
> 
> Yes, I like this comment more than mine. Andrew could you replace it in
> your tree or should I repost the patch?

I did this.

--- a/mm/page_alloc.c~mm-handle-uninitialized-numa-nodes-gracefully-fix
+++ a/mm/page_alloc.c
@@ -8155,12 +8155,16 @@ void __init free_area_init(unsigned long
 			}
 			arch_refresh_nodedata(nid, pgdat);
 			free_area_init_memoryless_node(nid);
+
 			/*
-			 * not marking this node online because we do not want to
-			 * confuse userspace by sysfs files/directories for node
-			 * without any memory attached to it (see topology_init)
-			 * The pgdat will get fully initialized when a memory is
-			 * hotpluged into it by hotadd_init_pgdat
+			 * We do not want to confuse userspace by sysfs
+			 * files/directories for node without any memory
+			 * attached to it, so this node is not marked as
+			 * N_MEMORY and not marked online so that no sysfs
+			 * hierarchy will be created via register_one_node for
+			 * it. The pgdat will get fully initialized by
+			 * hotadd_init_pgdat() when memory is hotplugged into
+			 * this node.
 			 */
 			continue;
 		}
_