[PATCH/RFC] AutoPage Migration - V0.1 - 7/8 add hysteresis to internode migration

Lee Schermerhorn
2006-03-10T19:54:59Z

AutoPage Migration - V0.1 - 7/8 add hysteresis to internode migration

This patch adds hysteresis to the internode migration to prevent
page migration trashing when scheduler driven page migration is
enabled.

Add static in-line function "too_soon_for_internode_migration"
[macro => 0 if !CONFIG_MIGRATION] to check for attempts to move
task to a new node sooner than sched_migrate_interval jiffies
after previous migration.

Modify try_to_wakeup() to leave task on its current cpu if too
soon to move it to a different node.

Modify can_migrate_task() to "just say no!" if the load balancer
proposes an internode migration too soon after previous internode
migration.

Added a control variable--sched_migrate_interval--to /sys/kernel/migration
to query/set the interval. Provide some fairly arbitrary min, max and
default values.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

Index: linux-2.6.16-rc5-git6/include/linux/sched.h
===================================================================
--- linux-2.6.16-rc5-git6.orig/include/linux/sched.h 2006-03-03 13:18:02.000000000 -0500
+++ linux-2.6.16-rc5-git6/include/linux/sched.h 2006-03-03 13:43:39.000000000 -0500
@@ -864,6 +864,7 @@ struct task_struct {
struct mempolicy *mempolicy;
short il_next;
#ifdef CONFIG_MIGRATION
+ unsigned long next_migrate; /* internode migration hysteresis */
int migrate_pending; /* internode mem migration pending */
#endif
#endif
Index: linux-2.6.16-rc5-git6/include/linux/auto-migrate.h
===================================================================
--- linux-2.6.16-rc5-git6.orig/include/linux/auto-migrate.h 2006-03-03 13:18:02.000000000 -0500
+++ linux-2.6.16-rc5-git6/include/linux/auto-migrate.h 2006-03-03 13:43:39.000000000 -0500
@@ -13,6 +13,12 @@

extern int sched_migrate_memory; /* sysctl: enable/disable */

+extern unsigned long sched_migrate_interval; /* sysctl: seconds <=> jiffies */
+#define SCHED_MIGRATE_INTERVAL_DFLT (30*HZ)
+#define SCHED_MIGRATE_INTERVAL_MIN (5*HZ)
+#define SCHED_MIGRATE_INTERVAL_MAX (300*HZ)
+
+
#ifdef _LINUX_SCHED_H /* only used where this is defined */
static inline void check_internode_migration(task_t *task, int dest_cpu)
{
@@ -32,6 +38,25 @@ static inline void check_internode_migra
}
}

+/*
+ * To avoids page migration thrashing when memory migration is enabled,
+ * check user task for too recent internode migration.
+ */
+static inline int too_soon_for_internode_migration(task_t *task,
+ int this_cpu)
+{
+ if (sched_migrate_memory &&
+ task->mm && !(task->flags & PF_BORROWED_MM) &&
+ cpu_to_node(task_cpu(task)) != cpu_to_node(this_cpu)) {
+
+ if (task->migrate_pending ||
+ time_before(jiffies, task->next_migrate))
+ return 1;
+ }
+
+ return 0;
+}
+
extern void migrate_task_memory(void);

static inline void check_migrate_pending(void)
@@ -56,6 +81,7 @@ static inline void check_migrate_pending
}

migrate_task_memory();
+ current->next_migrate = jiffies + sched_migrate_interval;

if (likely(disable_irqs))
local_irq_disable();
@@ -71,6 +97,7 @@ out:
#else /* !CONFIG_MIGRATION */

#define check_internode_migration(t,c) /* NOTHING */
+#define too_soon_for_internode_migration(t,c) 0

#define check_migrate_pending() /* NOTHING */

Index: linux-2.6.16-rc5-git6/mm/mempolicy.c
===================================================================
--- linux-2.6.16-rc5-git6.orig/mm/mempolicy.c 2006-03-03 13:18:02.000000000 -0500
+++ linux-2.6.16-rc5-git6/mm/mempolicy.c 2006-03-03 15:55:22.000000000 -0500
@@ -87,6 +87,7 @@
#include <linux/seq_file.h>
#include <linux/proc_fs.h>
#include <linux/sysfs.h>
+#include <linux/auto-migrate.h>

#include <asm/tlbflush.h>
#include <asm/uaccess.h>
@@ -153,12 +154,46 @@ static ssize_t sched_migrate_memory_stor
}
MIGRATION_ATTR_RW(sched_migrate_memory);

+/*
+ * sched_migrate_interval: minimum interval between internode
+ * task migration when 'sched_memory_migrate' enabled.
+ * units: jiffies
+ */
+unsigned long sched_migrate_interval = SCHED_MIGRATE_INTERVAL_DFLT;
+
+//TODO: __setup function for boot command option
+
+static ssize_t sched_migrate_interval_show(struct subsystem *subsys,
+ char *page)
+{
+ return sprintf(page, "sched_migrate_interval %ld\n",
+ sched_migrate_interval/HZ );
+}
+static ssize_t sched_migrate_interval_store(struct subsystem *subsys,
+ const char *page, size_t count)
+{
+ unsigned long n = simple_strtoul(page, NULL, 10) * HZ;
+
+ /*
+ * silently clip to min/max
+ */
+ if (n < SCHED_MIGRATE_INTERVAL_MIN)
+ sched_migrate_interval = SCHED_MIGRATE_INTERVAL_MIN;
+ else if (n > SCHED_MIGRATE_INTERVAL_MAX)
+ sched_migrate_interval = SCHED_MIGRATE_INTERVAL_MAX;
+ else
+ sched_migrate_interval = n;
+ return count;
+}
+MIGRATION_ATTR_RW(sched_migrate_interval);
+

decl_subsys(migration, NULL, NULL);
EXPORT_SYMBOL(migration_subsys);

static struct attribute *migration_attrs[] = {
&sched_migrate_memory_attr.attr,
+ &sched_migrate_interval_attr.attr,
NULL
};

Index: linux-2.6.16-rc5-git6/kernel/sched.c
===================================================================
--- linux-2.6.16-rc5-git6.orig/kernel/sched.c 2006-03-03 13:32:07.000000000 -0500
+++ linux-2.6.16-rc5-git6/kernel/sched.c 2006-03-03 13:43:39.000000000 -0500
@@ -1206,7 +1206,8 @@ static int try_to_wake_up(task_t *p, uns
}
}

- if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
+ if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)
+ || too_soon_for_internode_migration(p, this_cpu)))
goto out_set_cpu;

/*
@@ -1808,6 +1809,7 @@ int can_migrate_task(task_t *p, runqueue
* 1) running (obviously), or
* 2) cannot be migrated to this CPU due to cpus_allowed, or
* 3) are cache-hot on their current CPU.
+ * 4) too soon since last internode migration
*/
if (!cpu_isset(this_cpu, p->cpus_allowed))
return 0;
@@ -1816,6 +1818,10 @@ int can_migrate_task(task_t *p, runqueue
if (task_running(rq, p))
return 0;

+// TODO: should this be under Agressive migration?
+ if (too_soon_for_internode_migration(p, this_cpu))
+ return 0;
+
/*
* Aggressive migration if:
* 1) task is cache cold, or

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: email@kvack.org