linux-kernel - Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc

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Message-Id: <20170601213310.uzal6zihfbxazysx@arbab-laptop.localdomain>
Date:   Thu, 1 Jun 2017 16:33:10 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Shailendra Singh <shailendras@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc

On Thu, Jun 01, 2017 at 07:36:31PM +1000, Michael Ellerman wrote:
>I don't think that's what the patch does. It just marks 32 (!?) nodes 
>as online. Or if you're talking about reverting 3af229f2071f that 
>leaves you with 256 possible nodes. Both of which are wasteful.

To be clear, with Balbir's set the latter is no longer wasteful.

>The right fix is to make sure any nodes which are present at boot 
>remain in the possible map, even if they don't have memory/CPUs 
>assigned at boot.

I'm still hoping 3af229f2071f could indeed be reverted some day, but 
until then the following would follow your suggestion for our GPU nodes.  
What do you think?

--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -895,6 +895,7 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
 void __init initmem_init(void)
 {
 	int nid, cpu;
+	struct device_node *dn;
 
 	max_low_pfn = memblock_end_of_DRAM() >> PAGE_SHIFT;
 	max_pfn = max_low_pfn;
@@ -911,6 +912,18 @@ void __init initmem_init(void)
 	 */
 	nodes_and(node_possible_map, node_possible_map, node_online_map);
 
+	/*
+	 * Consider an ibm,coherent-device-memory node possible. Even though
+	 * it is not online at boot, it may be hotplugged later.
+	 */
+	for_each_compatible_node(dn, NULL, "ibm,coherent-device-memory") {
+		nid = of_node_to_nid_single(dn);
+		if (nid < 0)
+			continue;
+
+		node_set(nid, node_possible_map);
+	}
+
 	for_each_online_node(nid) {
 		unsigned long start_pfn, end_pfn;
 

-- 
Reza Arbab