[PATCH 1/3] mm, sysctl: make VM stats configurable

[Kemi Wang]

This patch adds a tunable interface that allows VM stats configurable, as
suggested by Dave Hansen and Ying Huang.

When performance becomes a bottleneck and you can tolerate some possible
tool breakage and some decreased counter precision (e.g. numa counter), you
can do:
	echo [C|c]oarse > /proc/sys/vm/vmstat_mode

When performance is not a bottleneck and you want all tooling to work, you
can do:
	echo [S|s]trict > /proc/sys/vm/vmstat_mode

We recommend automatic detection of virtual memory statistics by system,
this is also system default configuration, you can do:
	echo [A|a]uto > /proc/sys/vm/vmstat_mode

The next patch handles numa statistics distinctively based-on different VM
stats mode.

Reported-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
Suggested-by: Ying Huang <ying.huang@xxxxxxxxx>
Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx>
---
 include/linux/vmstat.h | 14 ++++++++++
 kernel/sysctl.c        |  7 +++++
 mm/vmstat.c            | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 91 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index ade7cb5..c3634c7 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -9,6 +9,20 @@
 
 extern int sysctl_stat_interval;
 
+/*
+ * vmstat_mode:
+ * 0 = auto mode of vmstat, automatic detection of VM statistics.
+ * 1 = strict mode of vmstat, keep all VM statistics.
+ * 2 = coarse mode of vmstat, ignore unimportant VM statistics.
+ */
+#define VMSTAT_AUTO_MODE 0
+#define VMSTAT_STRICT_MODE  1
+#define VMSTAT_COARSE_MODE  2
+#define VMSTAT_MODE_LEN 16
+extern char sysctl_vmstat_mode[];
+extern int sysctl_vmstat_mode_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *length, loff_t *ppos);
+
 #ifdef CONFIG_VM_EVENT_COUNTERS
 /*
  * Light weight per cpu counter implementation.
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6648fbb..f5b813b 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1234,6 +1234,13 @@ static struct ctl_table kern_table[] = {
 
 static struct ctl_table vm_table[] = {
 	{
+		.procname	= "vmstat_mode",
+		.data		= &sysctl_vmstat_mode,
+		.maxlen		= VMSTAT_MODE_LEN,
+		.mode		= 0644,
+		.proc_handler	= sysctl_vmstat_mode_handler,
+	},
+	{
 		.procname	= "overcommit_memory",
 		.data		= &sysctl_overcommit_memory,
 		.maxlen		= sizeof(sysctl_overcommit_memory),
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4bb13e7..e675ad2 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -32,6 +32,76 @@
 
 #define NUMA_STATS_THRESHOLD (U16_MAX - 2)
 
+int vmstat_mode = VMSTAT_AUTO_MODE;
+char sysctl_vmstat_mode[VMSTAT_MODE_LEN] = "auto";
+static const char *vmstat_mode_name[3] = {"auto", "strict", "coarse"};
+static DEFINE_MUTEX(vmstat_mode_lock);
+
+
+static int __parse_vmstat_mode(char *s)
+{
+	const char *str = s;
+
+	if (strcmp(str, "auto") == 0 || strcmp(str, "Auto") == 0)
+		vmstat_mode = VMSTAT_AUTO_MODE;
+	else if (strcmp(str, "strict") == 0 || strcmp(str, "Strict") == 0)
+		vmstat_mode = VMSTAT_STRICT_MODE;
+	else if (strcmp(str, "coarse") == 0 || strcmp(str, "Coarse") == 0)
+		vmstat_mode = VMSTAT_COARSE_MODE;
+	else {
+		pr_warn("Ignoring invalid vmstat_mode value: %s\n", s);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+int sysctl_vmstat_mode_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *length, loff_t *ppos)
+{
+	char old_string[VMSTAT_MODE_LEN];
+	int ret, oldval;
+
+	mutex_lock(&vmstat_mode_lock);
+	if (write)
+		strncpy(old_string, (char *)table->data, VMSTAT_MODE_LEN);
+	ret = proc_dostring(table, write, buffer, length, ppos);
+	if (ret || !write) {
+		mutex_unlock(&vmstat_mode_lock);
+		return ret;
+	}
+
+	oldval = vmstat_mode;
+	if (__parse_vmstat_mode((char *)table->data)) {
+		/*
+		 * invalid sysctl_vmstat_mode value, restore saved string
+		 */
+		strncpy((char *)table->data, old_string, VMSTAT_MODE_LEN);
+		vmstat_mode = oldval;
+	} else {
+		/*
+		 * check whether vmstat mode changes or not
+		 */
+		if (vmstat_mode == oldval) {
+			/* no change */
+			mutex_unlock(&vmstat_mode_lock);
+			return 0;
+		} else if (vmstat_mode == VMSTAT_AUTO_MODE)
+			pr_info("vmstat mode changes from %s to auto mode\n",
+					vmstat_mode_name[oldval]);
+		else if (vmstat_mode == VMSTAT_STRICT_MODE)
+			pr_info("vmstat mode changes from %s to strict mode\n",
+					vmstat_mode_name[oldval]);
+		else if (vmstat_mode == VMSTAT_COARSE_MODE)
+			pr_info("vmstat mode changes from %s to coarse mode\n",
+					vmstat_mode_name[oldval]);
+		else
+			pr_warn("invalid vmstat_mode:%d\n", vmstat_mode);
+	}
+
+	mutex_unlock(&vmstat_mode_lock);
+	return 0;
+}
+
 #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