In current kernel code, we only call node_set_state(cpu_to_node(cpu),
N_CPU) when a cpu is hot plugged. But we do not set the node state for
N_CPU when the cpus are brought online during boot.
So this could lead to failure when we check to see
if a node contains cpu with node_state(node_id, N_CPU).
One use case is in the node_reclaime function:
/*
* Only run node reclaim on the local node or on nodes that do
* not
* have associated processors. This will favor the local
* processor
* over remote processors and spread off node memory allocations
* as wide as possible.
*/
if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id !=
numa_node_id())
return NODE_RECLAIM_NOSCAN;
I instrumented the kernel to call this function after boot and it
always returns 0 on a x86 desktop machine until I apply
the attached patch.
int num_cpu_node(void)
{
int i, nr_cpu_nodes = 0;
for_each_node(i) {
if (node_state(i, N_CPU))
++ nr_cpu_nodes;
}
return nr_cpu_nodes;
}
Fix this by checking each node for online CPU when we initialize
vmstat that's responsible for maintaining node state.
v2:
1. Fix the problem for all architectures in the generic path
inside vmstat, not just for x86.
Signed-off-by: Tim Chen <tim.c.c...@linux.intel.com>
---
mm/vmstat.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 89cec42..d83f953 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1794,6 +1794,16 @@ static void __init start_shepherd_timer(void)
round_jiffies_relative(sysctl_stat_interval));
}
+static void __init init_cpu_node_state(void)
+{
+ int cpu;
+
+ get_online_cpus();
+ for_each_online_cpu(cpu)
+ node_set_state(cpu_to_node(cpu), N_CPU);
+ put_online_cpus();
+}
+
static void vmstat_cpu_dead(int node)
{
int cpu;
@@ -1851,6 +1861,7 @@ static int __init setup_vmstat(void)
#ifdef CONFIG_SMP
cpu_notifier_register_begin();
__register_cpu_notifier(&vmstat_notifier);
+ init_cpu_node_state();
start_shepherd_timer();
cpu_notifier_register_done();
--
2.5.5
