mm: sched: numa: Control enabling and disabling of NUMA balancing

This patch adds Kconfig options and kernel parameters to allow the
enabling and disabling of automatic NUMA balancing. The existance
of such a switch was and is very important when debugging problems
related to transparent hugepages and we should have the same for
automatic NUMA placement.

Signed-off-by: Mel Gorman <mgorman@suse.de>

7 files changed, 101 insertions, 17 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9776f068306b..2e8d2625b814 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1996,6 +1996,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
         nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
 
+        numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
+                        Allowed values are enable and disable
+
         numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
                         one of ['zone', 'node', 'default'] can be specified
                         This can be set from sysctl after boot.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0f4ff2bd03f6..b1e619f9ff1a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1563,10 +1563,14 @@ struct task_struct {
 
 #ifdef CONFIG_NUMA_BALANCING
 extern void task_numa_fault(int node, int pages, bool migrated);
+extern void set_numabalancing_state(bool enabled);
 #else
 static inline void task_numa_fault(int node, int pages, bool migrated)
 {
 }
+static inline void set_numabalancing_state(bool enabled)
+{
+}
 #endif
 
 /*
diff --git a/init/Kconfig b/init/Kconfig
index 9f00f004796a..18e2a5920a34 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -720,6 +720,14 @@ config ARCH_USES_NUMA_PROT_NONE
         depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
         depends on NUMA_BALANCING
 
+config NUMA_BALANCING_DEFAULT_ENABLED
+        bool "Automatically enable NUMA aware memory/task placement"
+        default y
+        depends on NUMA_BALANCING
+        help
+          If set, autonumic NUMA balancing will be enabled if running on a NUMA
+          machine.
+
 config NUMA_BALANCING
         bool "Memory placement aware NUMA scheduler"
         default y
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9d255bc0e278..7a45015274ab 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -192,23 +192,10 @@ static void sched_feat_disable(int i) { };
 static void sched_feat_enable(int i) { };
 #endif /* HAVE_JUMP_LABEL */
 
-static ssize_t
-sched_feat_write(struct file *filp, const char __user *ubuf,
-                size_t cnt, loff_t *ppos)
+static int sched_feat_set(char *cmp)
 {
-        char buf[64];
-        char *cmp;
-        int neg = 0;
         int i;
-
-        if (cnt > 63)
-                cnt = 63;
-
-        if (copy_from_user(&buf, ubuf, cnt))
-                return -EFAULT;
-
-        buf[cnt] = 0;
-        cmp = strstrip(buf);
+        int neg = 0;
 
         if (strncmp(cmp, "NO_", 3) == 0) {
                 neg = 1;
@@ -228,6 +215,27 @@ sched_feat_write(struct file *filp, const char __user *ubuf,
                 }
         }
 
+        return i;
+}
+
+static ssize_t
+sched_feat_write(struct file *filp, const char __user *ubuf,
+                size_t cnt, loff_t *ppos)
+{
+        char buf[64];
+        char *cmp;
+        int i;
+
+        if (cnt > 63)
+                cnt = 63;
+
+        if (copy_from_user(&buf, ubuf, cnt))
+                return -EFAULT;
+
+        buf[cnt] = 0;
+        cmp = strstrip(buf);
+
+        i = sched_feat_set(cmp);
         if (i == __SCHED_FEAT_NR)
                 return -EINVAL;
 
@@ -1549,6 +1557,16 @@ static void __sched_fork(struct task_struct *p)
 #endif /* CONFIG_NUMA_BALANCING */
 }
 
+#ifdef CONFIG_NUMA_BALANCING
+void set_numabalancing_state(bool enabled)
+{
+        if (enabled)
+                sched_feat_set("NUMA");
+        else
+                sched_feat_set("NO_NUMA");
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
 /*
  * fork()/clone()-time setup:
  */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4b577863933f..7a02a2082e95 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -811,6 +811,9 @@ void task_numa_fault(int node, int pages, bool migrated)
 {
         struct task_struct *p = current;
 
+        if (!sched_feat_numa(NUMA))
+                return;
+
         /* FIXME: Allocate task-specific structure for placement policy here */
 
         /*
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 5fb7aefbec80..d2373a3e3252 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -63,8 +63,10 @@ SCHED_FEAT(RT_RUNTIME_SHARE, true)
 SCHED_FEAT(LB_MIN, false)
 
 /*
- * Apply the automatic NUMA scheduling policy
+ * Apply the automatic NUMA scheduling policy. Enabled automatically
+ * at runtime if running on a NUMA machine. Can be controlled via
+ * numa_balancing=
  */
 #ifdef CONFIG_NUMA_BALANCING
-SCHED_FEAT(NUMA,        true)
+SCHED_FEAT(NUMA,        false)
 #endif
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index fd20e28fd2ad..046308e9b999 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2521,6 +2521,50 @@ void mpol_free_shared_policy(struct shared_policy *p)
         mutex_unlock(&p->mutex);
 }
 
+#ifdef CONFIG_NUMA_BALANCING
+static bool __initdata numabalancing_override;
+
+static void __init check_numabalancing_enable(void)
+{
+        bool numabalancing_default = false;
+
+        if (IS_ENABLED(CONFIG_NUMA_BALANCING_DEFAULT_ENABLED))
+                numabalancing_default = true;
+
+        if (nr_node_ids > 1 && !numabalancing_override) {
+                printk(KERN_INFO "Enabling automatic NUMA balancing. "
+                        "Configure with numa_balancing= or sysctl");
+                set_numabalancing_state(numabalancing_default);
+        }
+}
+
+static int __init setup_numabalancing(char *str)
+{
+        int ret = 0;
+        if (!str)
+                goto out;
+        numabalancing_override = true;
+
+        if (!strcmp(str, "enable")) {
+                set_numabalancing_state(true);
+                ret = 1;
+        } else if (!strcmp(str, "disable")) {
+                set_numabalancing_state(false);
+                ret = 1;
+        }
+out:
+        if (!ret)
+                printk(KERN_WARNING "Unable to parse numa_balancing=\n");
+
+        return ret;
+}
+__setup("numa_balancing=", setup_numabalancing);
+#else
+static inline void __init check_numabalancing_enable(void)
+{
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
 /* assumes fs == KERNEL_DS */
 void __init numa_policy_init(void)
 {
@@ -2571,6 +2615,8 @@ void __init numa_policy_init(void)
 
         if (do_set_mempolicy(MPOL_INTERLEAVE, 0, &interleave_nodes))
                 printk("numa_policy_init: interleaving failed\n");
+
+        check_numabalancing_enable();
 }
 
 /* Reset policy of current process to default */