[RFC v2 5/6] mm, migrc: Add a sysctl knob to enable/disable MIGRC mechanism

[Byungchul Park]

Add a sysctl knob, '/proc/sys/vm/migrc_enable' to switch on/off migrc.

Signed-off-by: Byungchul Park <byungchul@xxxxxx>
---
 mm/migrate.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index badef3d89c6c..c57536a0b2a6 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -59,6 +59,48 @@
 #include "internal.h"
 
 #ifdef CONFIG_MIGRC
+static int sysctl_migrc_enable = 1;
+#ifdef CONFIG_SYSCTL
+static int sysctl_migrc_enable_handler(struct ctl_table *table, int write,
+		void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table t;
+	int err;
+	int enabled = sysctl_migrc_enable;
+
+	if (write && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	t = *table;
+	t.data = &enabled;
+	err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
+	if (err < 0)
+		return err;
+	if (write)
+		sysctl_migrc_enable = enabled;
+	return err;
+}
+
+static struct ctl_table migrc_sysctls[] = {
+	{
+		.procname	= "migrc_enable",
+		.data		= NULL, /* filled in by handler */
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= sysctl_migrc_enable_handler,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE,
+	},
+	{}
+};
+
+static int __init migrc_sysctl_init(void)
+{
+	register_sysctl_init("vm", migrc_sysctls);
+	return 0;
+}
+late_initcall(migrc_sysctl_init);
+#endif
 
 /*
  * TODO: Yeah, it's a non-sense magic number. This simple value manages
@@ -288,6 +330,7 @@ int migrc_pending_nr_in_zone(struct zone *z)
 
 }
 #else
+static const int sysctl_migrc_enable;
 static inline bool migrc_src_pending(struct folio *f) { return false; }
 static inline bool migrc_dst_pending(struct folio *f) { return false; }
 static inline bool migrc_is_full(int nid) { return true; }
@@ -1878,8 +1921,9 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
 	VM_WARN_ON_ONCE(mode != MIGRATE_ASYNC &&
 			!list_empty(from) && !list_is_singular(from));
 
-	migrc_cond1 = (reason == MR_DEMOTION && current_is_kswapd()) ||
-		      (reason == MR_NUMA_MISPLACED);
+	migrc_cond1 = sysctl_migrc_enable &&
+		      ((reason == MR_DEMOTION && current_is_kswapd()) ||
+		      (reason == MR_NUMA_MISPLACED));
 
 	if (migrc_cond1)
 		migrc_req_start();
-- 
2.17.1