linux-kernel - Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline

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Date:   Mon, 10 Dec 2018 13:37:38 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH] mm/alloc: fallback to first node if the wanted node
 offline

On Fri 07-12-18 16:56:27, Michal Hocko wrote:
> On Fri 07-12-18 22:27:13, Pingfan Liu wrote:
> [...]
> > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> > index 1308f54..4dc497d 100644
> > --- a/arch/x86/mm/numa.c
> > +++ b/arch/x86/mm/numa.c
> > @@ -754,18 +754,23 @@ void __init init_cpu_to_node(void)
> >  {
> >         int cpu;
> >         u16 *cpu_to_apicid = early_per_cpu_ptr(x86_cpu_to_apicid);
> > +       int node, nr;
> > 
> >         BUG_ON(cpu_to_apicid == NULL);
> > +       nr = cpumask_weight(cpu_possible_mask);
> > +
> > +       /* bring up all possible node, since dev->numa_node */
> > +       //should check acpi works for node possible,
> > +       for_each_node(node)
> > +               if (!node_online(node))
> > +                       init_memory_less_node(node);
> 
> I suspect there is no change if you replace for_each_node by
> 	for_each_node_mask(nid, node_possible_map)
> 
> here. If that is the case then we are probably calling
> free_area_init_node too early. I do not see it yet though.

OK, so it is not about calling it late or soon. It is just that
node_possible_map is a misnomer and it has a different semantic than
I've expected. numa_nodemask_from_meminfo simply considers only nodes
with some memory. So my patch didn't really make any difference and the
node stayed uninialized.

In other words. Does the following work? I am sorry to wildguess this
way but I am not able to recreate your setups to play with this myself.

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index 1308f5408bf7..d51643e10d00 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -216,8 +216,6 @@ static void __init alloc_node_data(int nid)
 
 	node_data[nid] = nd;
 	memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
-
-	node_set_online(nid);
 }
 
 /**
@@ -527,6 +525,19 @@ static void __init numa_clear_kernel_node_hotplug(void)
 	}
 }
 
+static void __init init_memory_less_node(int nid)
+{
+	unsigned long zones_size[MAX_NR_ZONES] = {0};
+	unsigned long zholes_size[MAX_NR_ZONES] = {0};
+
+	free_area_init_node(nid, zones_size, 0, zholes_size);
+
+	/*
+	 * All zonelists will be built later in start_kernel() after per cpu
+	 * areas are initialized.
+	 */
+}
+
 static int __init numa_register_memblks(struct numa_meminfo *mi)
 {
 	unsigned long uninitialized_var(pfn_align);
@@ -570,7 +581,7 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
 		return -EINVAL;
 
 	/* Finally register nodes. */
-	for_each_node_mask(nid, node_possible_map) {
+	for_each_node(nid) {
 		u64 start = PFN_PHYS(max_pfn);
 		u64 end = 0;
 
@@ -592,6 +603,10 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
 			continue;
 
 		alloc_node_data(nid);
+		if (!end)
+			init_memory_less_node(nid);
+		else
+			node_set_online(nid);
 	}
 
 	/* Dump memblock with node info and return. */
@@ -721,21 +736,6 @@ void __init x86_numa_init(void)
 	numa_init(dummy_numa_init);
 }
 
-static void __init init_memory_less_node(int nid)
-{
-	unsigned long zones_size[MAX_NR_ZONES] = {0};
-	unsigned long zholes_size[MAX_NR_ZONES] = {0};
-
-	/* Allocate and initialize node data. Memory-less node is now online.*/
-	alloc_node_data(nid);
-	free_area_init_node(nid, zones_size, 0, zholes_size);
-
-	/*
-	 * All zonelists will be built later in start_kernel() after per cpu
-	 * areas are initialized.
-	 */
-}
-
 /*
  * Setup early cpu_to_node.
  *
@@ -763,9 +763,6 @@ void __init init_cpu_to_node(void)
 		if (node == NUMA_NO_NODE)
 			continue;
 
-		if (!node_online(node))
-			init_memory_less_node(node);
-
 		numa_set_node(cpu, node);
 	}
 }
-- 
Michal Hocko
SUSE Labs