Re: [PATCH v4] mm, sysctl: make NUMA stats configurable

On 2017年10月17日 15:54, Michal Hocko wrote:

On Tue 17-10-17 09:20:58, Kemi Wang wrote:
[...]

Other than two remarks below, it looks good to me and it also looks
simpler.

quoted

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4bb13e7..e746ed1 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c

@@ -32,6 +32,76 @@
 
 #define NUMA_STATS_THRESHOLD (U16_MAX - 2)
 
+#ifdef CONFIG_NUMA
+int sysctl_vm_numa_stat = ENABLE_NUMA_STAT;
+static DEFINE_MUTEX(vm_numa_stat_lock);

You can scope this mutex to the sysctl handler function

OK, thanks.

quoted

+int sysctl_vm_numa_stat_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *length, loff_t *ppos)
+{
+	int ret, oldval;
+
+	mutex_lock(&vm_numa_stat_lock);
+	if (write)
+		oldval = sysctl_vm_numa_stat;
+	ret = proc_dointvec(table, write, buffer, length, ppos);
+	if (ret || !write)
+		goto out;
+
+	if (oldval == sysctl_vm_numa_stat)
+		goto out;
+	else if (oldval == DISABLE_NUMA_STAT) {

So basically any value will enable numa stats. This means that we would
never be able to extend this interface to e.g. auto mode (say value 2).
I guess you meant to check sysctl_vm_numa_stat == ENABLE_NUMA_STAT?

I meant to make it more general other than ENABLE_NUMA_STAT(non 0 is enough), 
but it will make it hard to scale, as you said.
So, it would be like this:
0 -- disable
1 -- enable
other value is invalid.

May add option 2 later for auto if necessary:)

quoted

+		static_branch_enable(&vm_numa_stat_key);
+		pr_info("enable numa statistics\n");
+	} else if (sysctl_vm_numa_stat == DISABLE_NUMA_STAT) {
+		static_branch_disable(&vm_numa_stat_key);
+		invalid_numa_statistics();
+		pr_info("disable numa statistics, and clear numa counters\n");
+	}
+
+out:
+	mutex_unlock(&vm_numa_stat_lock);
+	return ret;
+}
+#endif
+
 #ifdef CONFIG_VM_EVENT_COUNTERS
 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
 EXPORT_PER_CPU_SYMBOL(vm_event_states);
-- 
2.7.4