Re: [PATCH 2.6.17-rc1-mm1 7/9] AutoPage Migration - V0.2 - add hysteresis to internode migration

Lee Schermerhorn
2006-04-07T20:41:18Z

AutoPage Migration - V0.2 - 7/9 add hysteresis to internode migration

V0.2: moved to mm/migrate.c; renamed to "auto_migrate_interval"

This patch adds hysteresis to the internode migration to prevent
page migration trashing when automatic 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 auto_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--auto_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-2.6.17-rc1-mm1/include/linux/sched.h
===================================================================
--- linux-2.6.17-rc1-mm1.orig/include/linux/sched.h 2006-04-05 10:15:00.000000000 -0400
+++ linux-2.6.17-rc1-mm1/include/linux/sched.h 2006-04-05 10:16:26.000000000 -0400
@@ -909,6 +909,7 @@ 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-2.6.17-rc1-mm1/mm/migrate.c
===================================================================
--- linux-2.6.17-rc1-mm1.orig/mm/migrate.c 2006-04-05 10:14:58.000000000 -0400
+++ linux-2.6.17-rc1-mm1/mm/migrate.c 2006-04-05 10:16:26.000000000 -0400
@@ -26,6 +26,7 @@
#include <linux/cpuset.h>
#include <linux/swapops.h>
#include <linux/sysfs.h>
+#include <linux/auto-migrate.h>

#include "internal.h"

@@ -73,11 +74,45 @@ static ssize_t auto_migrate_enable_store
}
MIGRATION_ATTR_RW(auto_migrate_enable);

+/*
+ * auto_migrate_interval: minimum interval between internode
+ * task migration when auto-migration enabled.
+ * units: jiffies
+ */
+unsigned long auto_migrate_interval = AUTO_MIGRATE_INTERVAL_DFLT;
+
+//TODO: __setup function for boot command option
+
+static ssize_t auto_migrate_interval_show(struct subsystem *subsys,
+ char *page)
+{
+ return sprintf(page, "auto_migrate_interval %ld\n",
+ auto_migrate_interval/HZ );
+}
+static ssize_t auto_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 < AUTO_MIGRATE_INTERVAL_MIN)
+ auto_migrate_interval = AUTO_MIGRATE_INTERVAL_MIN;
+ else if (n > AUTO_MIGRATE_INTERVAL_MAX)
+ auto_migrate_interval = AUTO_MIGRATE_INTERVAL_MAX;
+ else
+ auto_migrate_interval = n;
+ return count;
+}
+MIGRATION_ATTR_RW(auto_migrate_interval);
+
decl_subsys(migration, NULL, NULL);
EXPORT_SYMBOL(migration_subsys);

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

Index: linux-2.6.17-rc1-mm1/include/linux/auto-migrate.h
===================================================================
--- linux-2.6.17-rc1-mm1.orig/include/linux/auto-migrate.h 2006-04-05 10:15:00.000000000 -0400
+++ linux-2.6.17-rc1-mm1/include/linux/auto-migrate.h 2006-04-05 10:16:26.000000000 -0400
@@ -15,6 +15,11 @@ extern void auto_migrate_task_memory(voi

extern int auto_migrate_enable;

+extern unsigned long auto_migrate_interval; /* seconds <=> jiffies */
+#define AUTO_MIGRATE_INTERVAL_DFLT (30*HZ)
+#define AUTO_MIGRATE_INTERVAL_MIN (5*HZ)
+#define AUTO_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)
{
@@ -33,6 +38,25 @@ static inline void check_internode_migra
}
}

+/*
+ * To avoids page migration thrashing when auto 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 (auto_migrate_enable &&
+ 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;
+}
+
static inline void check_migrate_pending(void)
{
if (!auto_migrate_enable)
@@ -55,6 +79,7 @@ static inline void check_migrate_pending
}

auto_migrate_task_memory();
+ current->next_migrate = jiffies + auto_migrate_interval;

if (likely(disable_irqs))
local_irq_disable();
@@ -70,6 +95,7 @@ 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-2.6.17-rc1-mm1/kernel/sched.c
===================================================================
--- linux-2.6.17-rc1-mm1.orig/kernel/sched.c 2006-04-05 10:16:13.000000000 -0400
+++ linux-2.6.17-rc1-mm1/kernel/sched.c 2006-04-05 10:16:26.000000000 -0400
@@ -1378,7 +1378,8 @@ 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;

/*
@@ -2013,6 +2014,7 @@ 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;
@@ -2021,6 +2023,10 @@ 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