xen: tmem: self-ballooning and frontswap-selfshrinking

	  the system to expand the domain's memory allocation, or alternatively

	  return unneeded memory to the system.

config XEN_SELFBALLOONING

	bool "Dynamically self-balloon kernel memory to target"

	depends on XEN && XEN_BALLOON && CLEANCACHE && SWAP

	default n

	help

	  Self-ballooning dynamically balloons available kernel memory driven

	  by the current usage of anonymous memory ("committed AS") and

	  controlled by various sysfs-settable parameters.  Configuring

	  FRONTSWAP is highly recommended; if it is not configured, self-

	  ballooning is disabled by default but can be enabled with the

	  'selfballooning' kernel boot parameter.  If FRONTSWAP is configured,

	  frontswap-selfshrinking is enabled by default but can be disabled

	  with the 'noselfshrink' kernel boot parameter; and self-ballooning

	  is enabled by default but can be disabled with the 'noselfballooning'

	  kernel boot parameter.  Note that systems without a sufficiently

	  large swap device should not enable self-ballooning.

config XEN_SCRUB_PAGES

	bool "Scrub pages before returning them to system"

	depends on XEN_BALLOON

obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o

obj-$(CONFIG_XEN_XENCOMM)		+= xencomm.o

obj-$(CONFIG_XEN_BALLOON)		+= xen-balloon.o

obj-$(CONFIG_XEN_SELFBALLOONING)	+= xen-selfballoon.o

obj-$(CONFIG_XEN_DEV_EVTCHN)		+= xen-evtchn.o

obj-$(CONFIG_XEN_GNTDEV)		+= xen-gntdev.o

obj-$(CONFIG_XEN_GRANT_DEV_ALLOC)	+= xen-gntalloc.o

	register_balloon(&balloon_sysdev);

	register_xen_selfballooning(&balloon_sysdev);

	target_watch.callback = watch_target;

	xenstore_notifier.notifier_call = balloon_init_watcher;

/******************************************************************************

 * Xen selfballoon driver (and optional frontswap self-shrinking driver)

 *

 * Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.

 *

 * This code complements the cleancache and frontswap patchsets to optimize

 * support for Xen Transcendent Memory ("tmem").  The policy it implements

 * is rudimentary and will likely improve over time, but it does work well

 * enough today.

 *

 * Two functionalities are implemented here which both use "control theory"

 * (feedback) to optimize memory utilization. In a virtualized environment

 * such as Xen, RAM is often a scarce resource and we would like to ensure

 * that each of a possibly large number of virtual machines is using RAM

 * efficiently, i.e. using as little as possible when under light load

 * and obtaining as much as possible when memory demands are high.

 * Since RAM needs vary highly dynamically and sometimes dramatically,

 * "hysteresis" is used, that is, memory target is determined not just

 * on current data but also on past data stored in the system.

 *

 * "Selfballooning" creates memory pressure by managing the Xen balloon

 * driver to decrease and increase available kernel memory, driven

 * largely by the target value of "Committed_AS" (see /proc/meminfo).

 * Since Committed_AS does not account for clean mapped pages (i.e. pages

 * in RAM that are identical to pages on disk), selfballooning has the

 * affect of pushing less frequently used clean pagecache pages out of

 * kernel RAM and, presumably using cleancache, into Xen tmem where

 * Xen can more efficiently optimize RAM utilization for such pages.

 *

 * When kernel memory demand unexpectedly increases faster than Xen, via

 * the selfballoon driver, is able to (or chooses to) provide usable RAM,

 * the kernel may invoke swapping.  In most cases, frontswap is able

 * to absorb this swapping into Xen tmem.  However, due to the fact

 * that the kernel swap subsystem assumes swapping occurs to a disk,

 * swapped pages may sit on the disk for a very long time; even if

 * the kernel knows the page will never be used again.  This is because

 * the disk space costs very little and can be overwritten when

 * necessary.  When such stale pages are in frontswap, however, they

 * are taking up valuable real estate.  "Frontswap selfshrinking" works

 * to resolve this:  When frontswap activity is otherwise stable

 * and the guest kernel is not under memory pressure, the "frontswap

 * selfshrinking" accounts for this by providing pressure to remove some

 * pages from frontswap and return them to kernel memory.

 *

 * For both "selfballooning" and "frontswap-selfshrinking", a worker

 * thread is used and sysfs tunables are provided to adjust the frequency

 * and rate of adjustments to achieve the goal, as well as to disable one

 * or both functions independently.

 *

 * While some argue that this functionality can and should be implemented

 * in userspace, it has been observed that bad things happen (e.g. OOMs).

 *

 * System configuration note: Selfballooning should not be enabled on

 * systems without a sufficiently large swap device configured; for best

 * results, it is recommended that total swap be increased by the size

 * of the guest memory.  Also, while technically not required to be

 * configured, it is highly recommended that frontswap also be configured

 * and enabled when selfballooning is running.  So, selfballooning

 * is disabled by default if frontswap is not configured and can only

 * be enabled with the "selfballooning" kernel boot option; similarly

 * selfballooning is enabled by default if frontswap is configured and

 * can be disabled with the "noselfballooning" kernel boot option.  Finally,

 * when frontswap is configured, frontswap-selfshrinking can be disabled

 * with the "noselfshrink" kernel boot option.

 *

 * Selfballooning is disallowed in domain0 and force-disabled.

 *

 */

#include <linux/kernel.h>

#include <linux/mm.h>

#include <linux/mman.h>

#include <xen/balloon.h>

#include <xen/tmem.h>

/* Enable/disable with sysfs. */

static int xen_selfballooning_enabled __read_mostly;

/*

 * Controls rate at which memory target (this iteration) approaches

 * ultimate goal when memory need is increasing (up-hysteresis) or

 * decreasing (down-hysteresis). Higher values of hysteresis cause

 * slower increases/decreases. The default values for the various

 * parameters were deemed reasonable by experimentation, may be

 * workload-dependent, and can all be adjusted via sysfs.

 */

static unsigned int selfballoon_downhysteresis __read_mostly = 8;

static unsigned int selfballoon_uphysteresis __read_mostly = 1;

/* In HZ, controls frequency of worker invocation. */

static unsigned int selfballoon_interval __read_mostly = 5;

static void selfballoon_process(struct work_struct *work);

static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);

#ifdef CONFIG_FRONTSWAP

#include <linux/frontswap.h>

/* Enable/disable with sysfs. */

static bool frontswap_selfshrinking __read_mostly;

/* Enable/disable with kernel boot option. */

static bool use_frontswap_selfshrink __initdata = true;

/*

 * The default values for the following parameters were deemed reasonable

 * by experimentation, may be workload-dependent, and can all be

 * adjusted via sysfs.

 */

/* Control rate for frontswap shrinking. Higher hysteresis is slower. */

static unsigned int frontswap_hysteresis __read_mostly = 20;

/*

 * Number of selfballoon worker invocations to wait before observing that

 * frontswap selfshrinking should commence. Note that selfshrinking does

 * not use a separate worker thread.

 */

static unsigned int frontswap_inertia __read_mostly = 3;

/* Countdown to next invocation of frontswap_shrink() */

static unsigned long frontswap_inertia_counter;

/*

 * Invoked by the selfballoon worker thread, uses current number of pages

 * in frontswap (frontswap_curr_pages()), previous status, and control

 * values (hysteresis and inertia) to determine if frontswap should be

 * shrunk and what the new frontswap size should be.  Note that

 * frontswap_shrink is essentially a partial swapoff that immediately

 * transfers pages from the "swap device" (frontswap) back into kernel

 * RAM; despite the name, frontswap "shrinking" is very different from

 * the "shrinker" interface used by the kernel MM subsystem to reclaim

 * memory.

 */

static void frontswap_selfshrink(void)

{

	static unsigned long cur_frontswap_pages;

	static unsigned long last_frontswap_pages;

	static unsigned long tgt_frontswap_pages;

	last_frontswap_pages = cur_frontswap_pages;

	cur_frontswap_pages = frontswap_curr_pages();

	if (!cur_frontswap_pages ||

			(cur_frontswap_pages > last_frontswap_pages)) {

		frontswap_inertia_counter = frontswap_inertia;

		return;

	}

	if (frontswap_inertia_counter && --frontswap_inertia_counter)

		return;

	if (cur_frontswap_pages <= frontswap_hysteresis)

		tgt_frontswap_pages = 0;

	else

		tgt_frontswap_pages = cur_frontswap_pages -

			(cur_frontswap_pages / frontswap_hysteresis);

	frontswap_shrink(tgt_frontswap_pages);

}

static int __init xen_nofrontswap_selfshrink_setup(char *s)

{

	use_frontswap_selfshrink = false;

	return 1;

}

__setup("noselfshrink", xen_nofrontswap_selfshrink_setup);

/* Disable with kernel boot option. */

static bool use_selfballooning __initdata = true;

static int __init xen_noselfballooning_setup(char *s)

{

	use_selfballooning = false;

	return 1;

}

__setup("noselfballooning", xen_noselfballooning_setup);

#else /* !CONFIG_FRONTSWAP */

/* Enable with kernel boot option. */

static bool use_selfballooning __initdata = false;

static int __init xen_selfballooning_setup(char *s)

{

	use_selfballooning = true;

	return 1;

}

__setup("selfballooning", xen_selfballooning_setup);

#endif /* CONFIG_FRONTSWAP */

/*

 * Use current balloon size, the goal (vm_committed_as), and hysteresis

 * parameters to set a new target balloon size

 */

static void selfballoon_process(struct work_struct *work)

{

	unsigned long cur_pages, goal_pages, tgt_pages;

	bool reset_timer = false;

	if (xen_selfballooning_enabled) {

		cur_pages = balloon_stats.current_pages;

		tgt_pages = cur_pages; /* default is no change */

		goal_pages = percpu_counter_read_positive(&vm_committed_as) +

			balloon_stats.current_pages - totalram_pages;

#ifdef CONFIG_FRONTSWAP

		/* allow space for frontswap pages to be repatriated */

		if (frontswap_selfshrinking && frontswap_enabled)

			goal_pages += frontswap_curr_pages();

#endif

		if (cur_pages > goal_pages)

			tgt_pages = cur_pages -

				((cur_pages - goal_pages) /

				  selfballoon_downhysteresis);

		else if (cur_pages < goal_pages)

			tgt_pages = cur_pages +

				((goal_pages - cur_pages) /

				  selfballoon_uphysteresis);

		/* else if cur_pages == goal_pages, no change */

		balloon_set_new_target(tgt_pages);

		reset_timer = true;

	}

#ifdef CONFIG_FRONTSWAP

	if (frontswap_selfshrinking && frontswap_enabled) {

		frontswap_selfshrink();

		reset_timer = true;

	}

#endif

	if (reset_timer)

		schedule_delayed_work(&selfballoon_worker,

			selfballoon_interval * HZ);

}

#ifdef CONFIG_SYSFS

#include <linux/sysdev.h>

#include <linux/capability.h>

#define SELFBALLOON_SHOW(name, format, args...)				\

	static ssize_t show_##name(struct sys_device *dev,	\

					   struct sysdev_attribute *attr, \

					   char *buf) \

	{ \

		return sprintf(buf, format, ##args); \

	}

SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);

static ssize_t store_selfballooning(struct sys_device *dev,

			    struct sysdev_attribute *attr,

			    const char *buf,

			    size_t count)

{

	bool was_enabled = xen_selfballooning_enabled;

	unsigned long tmp;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &tmp);

	if (err || ((tmp != 0) && (tmp != 1)))

		return -EINVAL;

	xen_selfballooning_enabled = !!tmp;

	if (!was_enabled && xen_selfballooning_enabled)

		schedule_delayed_work(&selfballoon_worker,

			selfballoon_interval * HZ);

	return count;

}

static SYSDEV_ATTR(selfballooning, S_IRUGO | S_IWUSR,

		   show_selfballooning, store_selfballooning);

SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);

static ssize_t store_selfballoon_interval(struct sys_device *dev,

					  struct sysdev_attribute *attr,

					  const char *buf,

					  size_t count)

{

	unsigned long val;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &val);

	if (err || val == 0)

		return -EINVAL;

	selfballoon_interval = val;

	return count;

}

static SYSDEV_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,

		   show_selfballoon_interval, store_selfballoon_interval);

SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);

static ssize_t store_selfballoon_downhys(struct sys_device *dev,

					 struct sysdev_attribute *attr,

					 const char *buf,

					 size_t count)

{

	unsigned long val;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &val);

	if (err || val == 0)

		return -EINVAL;

	selfballoon_downhysteresis = val;

	return count;

}

static SYSDEV_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,

		   show_selfballoon_downhys, store_selfballoon_downhys);

SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);

static ssize_t store_selfballoon_uphys(struct sys_device *dev,

				       struct sysdev_attribute *attr,

				       const char *buf,

				       size_t count)

{

	unsigned long val;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &val);

	if (err || val == 0)

		return -EINVAL;

	selfballoon_uphysteresis = val;

	return count;

}

static SYSDEV_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,

		   show_selfballoon_uphys, store_selfballoon_uphys);

#ifdef CONFIG_FRONTSWAP

SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);

static ssize_t store_frontswap_selfshrinking(struct sys_device *dev,

					     struct sysdev_attribute *attr,

					     const char *buf,

					     size_t count)

{

	bool was_enabled = frontswap_selfshrinking;

	unsigned long tmp;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &tmp);

	if (err || ((tmp != 0) && (tmp != 1)))

		return -EINVAL;

	frontswap_selfshrinking = !!tmp;

	if (!was_enabled && !xen_selfballooning_enabled &&

	     frontswap_selfshrinking)

		schedule_delayed_work(&selfballoon_worker,

			selfballoon_interval * HZ);

	return count;

}

static SYSDEV_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,

		   show_frontswap_selfshrinking, store_frontswap_selfshrinking);

SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);

static ssize_t store_frontswap_inertia(struct sys_device *dev,

				       struct sysdev_attribute *attr,

				       const char *buf,

				       size_t count)

{

	unsigned long val;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &val);

	if (err || val == 0)

		return -EINVAL;

	frontswap_inertia = val;

	frontswap_inertia_counter = val;

	return count;

}

static SYSDEV_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,

		   show_frontswap_inertia, store_frontswap_inertia);

SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);

static ssize_t store_frontswap_hysteresis(struct sys_device *dev,

					  struct sysdev_attribute *attr,

					  const char *buf,

					  size_t count)

{

	unsigned long val;

	int err;

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	err = strict_strtoul(buf, 10, &val);

	if (err || val == 0)

		return -EINVAL;

	frontswap_hysteresis = val;

	return count;

}

static SYSDEV_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,

		   show_frontswap_hysteresis, store_frontswap_hysteresis);

#endif /* CONFIG_FRONTSWAP */

static struct attribute *selfballoon_attrs[] = {

	&attr_selfballooning.attr,

	&attr_selfballoon_interval.attr,

	&attr_selfballoon_downhysteresis.attr,

	&attr_selfballoon_uphysteresis.attr,

#ifdef CONFIG_FRONTSWAP

	&attr_frontswap_selfshrinking.attr,

	&attr_frontswap_hysteresis.attr,

	&attr_frontswap_inertia.attr,

#endif

	NULL

};

static struct attribute_group selfballoon_group = {

	.name = "selfballoon",

	.attrs = selfballoon_attrs

};

#endif

int register_xen_selfballooning(struct sys_device *sysdev)

{

	int error = -1;

#ifdef CONFIG_SYSFS

	error = sysfs_create_group(&sysdev->kobj, &selfballoon_group);

#endif

	return error;

}

EXPORT_SYMBOL(register_xen_selfballooning);

static int __init xen_selfballoon_init(void)

{

	bool enable = false;

	if (!xen_domain())

		return -ENODEV;

	if (xen_initial_domain()) {

		pr_info("xen/balloon: Xen selfballooning driver "

				"disabled for domain0.\n");

		return -ENODEV;

	}

	xen_selfballooning_enabled = tmem_enabled && use_selfballooning;

	if (xen_selfballooning_enabled) {

		pr_info("xen/balloon: Initializing Xen "

					"selfballooning driver.\n");

		enable = true;

	}

#ifdef CONFIG_FRONTSWAP

	frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;

	if (frontswap_selfshrinking) {

		pr_info("xen/balloon: Initializing frontswap "

					"selfshrinking driver.\n");

		enable = true;

	}

#endif

	if (!enable)

		return -ENODEV;

	schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);

	return 0;

}

subsys_initcall(xen_selfballoon_init);

MODULE_LICENSE("GPL");

int alloc_xenballooned_pages(int nr_pages, struct page** pages);

void free_xenballooned_pages(int nr_pages, struct page** pages);

struct sys_device;

#ifdef CONFIG_XEN_SELFBALLOONING

extern int register_xen_selfballooning(struct sys_device *sysdev);

#else

static inline int register_xen_selfballooning(struct sys_device *sysdev)

{

	return -ENOSYS;

}

#endif