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

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Date:   Thu, 27 Jan 2022 15:47:40 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, 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>,
        Wei Yang <richard.weiyang@...il.com>,
        Rafael Aquini <raquini@...hat.com>
Subject: Re: [PATCH 2/6] mm: handle uninitialized numa nodes gracefully

On Thu 27-01-22 15:37:23, Mike Rapoport wrote:
> On Thu, Jan 27, 2022 at 09:53:01AM +0100, Michal Hocko wrote:
[...]
> > +		if (!node_online(nid)) {
> > +			pr_warn("Node %d uninitialized by the platform. Please report with boot dmesg.\n", nid);
> 
> Do we assume that platform code must allocate node data for all nodes in
> the system? Because if we don't this warning is misleading.

At least x86 does that (init_cpu_to_node). Now that you brought that up
I guess you are right that this could be more misleading than helpful.
What about
			pr_info("Initializing node %d as memoryless\n", nid);
Is this better?

> > +
> > +			/* Allocator not initialized yet */
> > +			pgdat = arch_alloc_nodedata(nid);
> > +			if (!pgdat) {
> > +				pr_err("Cannot allocate %zuB for node %d.\n",
> > +						sizeof(*pgdat), nid);
> > +				continue;
> > +			}
> > +			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
> > +			 */
> > +			continue;
> 
> This can be made slightly more concise if we fall through after
> arch_refresh_nodedata(), e.g. something like
> 
> 			...
> 
> 			arch_refresh_nodedata(nid, pgdat);
> 		}
> 
> 		pgdat = NODE_DATA(nid);
> 		free_area_init_node(nid);
> 
> 		/*
> 		 * Do not mark memoryless 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
> 		 */
> 		if (!pgdat->node_present_pages)
> 			continue;
> 
> but I don't feel strongly about it.

I do not have strong preference either way. Unless this is considered
better by more people I would stick with what I have.
-- 
Michal Hocko
SUSE Labs