drivers/xen/xen-selfballoon.c - kernel/mindspeed - Git at Google

 /******************************************************************************
  * 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/bootmem.h>
 #include <linux/swap.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
 #include <linux/module.h>
 #include <linux/workqueue.h>
 #include <xen/balloon.h>
 #include <xen/tmem.h>
 #include <xen/xen.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;

 /*
  * Minimum usable RAM in MB for selfballooning target for balloon.
  * If non-zero, it is added to totalreserve_pages and self-ballooning
  * will not balloon below the sum.  If zero, a piecewise linear function
  * is calculated as a minimum and added to totalreserve_pages.  Note that
  * setting this value indiscriminately may cause OOMs and crashes.
  */
 static unsigned int selfballoon_min_usable_mb;

 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 */

 #define MB2PAGES(mb)	((mb) << (20 - PAGE_SHIFT))

 /*
  * 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, floor_pages;
 	unsigned long useful_pages;
 	bool reset_timer = false;

 	if (xen_selfballooning_enabled) {
 		cur_pages = totalram_pages;
 		tgt_pages = cur_pages; /* default is no change */
 		goal_pages = percpu_counter_read_positive(&vm_committed_as) +
 				totalreserve_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 */
 		useful_pages = max_pfn - totalreserve_pages;
 		if (selfballoon_min_usable_mb != 0)
 			floor_pages = totalreserve_pages +
 					MB2PAGES(selfballoon_min_usable_mb);
 		/* piecewise linear function ending in ~3% slope */
 		else if (useful_pages < MB2PAGES(16))
 			floor_pages = max_pfn; /* not worth ballooning */
 		else if (useful_pages < MB2PAGES(64))
 			floor_pages = totalreserve_pages + MB2PAGES(16) +
 					((useful_pages - MB2PAGES(16)) >> 1);
 		else if (useful_pages < MB2PAGES(512))
 			floor_pages = totalreserve_pages + MB2PAGES(40) +
 					((useful_pages - MB2PAGES(40)) >> 3);
 		else /* useful_pages >= MB2PAGES(512) */
 			floor_pages = totalreserve_pages + MB2PAGES(99) +
 					((useful_pages - MB2PAGES(99)) >> 5);
 		if (tgt_pages < floor_pages)
 			tgt_pages = floor_pages;
 		balloon_set_new_target(tgt_pages +
 			balloon_stats.current_pages - totalram_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);

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

 static ssize_t store_selfballoon_min_usable_mb(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_min_usable_mb = val;
 	return count;
 }

 static SYSDEV_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
 		   show_selfballoon_min_usable_mb,
 		   store_selfballoon_min_usable_mb);


 #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,
 	&attr_selfballoon_min_usable_mb.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");
	/******************************************************************************
	* 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/bootmem.h>
	#include <linux/swap.h>
	#include <linux/mm.h>
	#include <linux/mman.h>
	#include <linux/module.h>
	#include <linux/workqueue.h>
	#include <xen/balloon.h>
	#include <xen/tmem.h>
	#include <xen/xen.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;

	/*
	* Minimum usable RAM in MB for selfballooning target for balloon.
	* If non-zero, it is added to totalreserve_pages and self-ballooning
	* will not balloon below the sum. If zero, a piecewise linear function
	* is calculated as a minimum and added to totalreserve_pages. Note that
	* setting this value indiscriminately may cause OOMs and crashes.
	*/
	static unsigned int selfballoon_min_usable_mb;

	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 */

	#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))

	/*
	* 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, floor_pages;
	unsigned long useful_pages;
	bool reset_timer = false;

	if (xen_selfballooning_enabled) {
	cur_pages = totalram_pages;
	tgt_pages = cur_pages; /* default is no change */
	goal_pages = percpu_counter_read_positive(&vm_committed_as) +
	totalreserve_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 */
	useful_pages = max_pfn - totalreserve_pages;
	if (selfballoon_min_usable_mb != 0)
	floor_pages = totalreserve_pages +
	MB2PAGES(selfballoon_min_usable_mb);
	/* piecewise linear function ending in ~3% slope */
	else if (useful_pages < MB2PAGES(16))
	floor_pages = max_pfn; /* not worth ballooning */
	else if (useful_pages < MB2PAGES(64))
	floor_pages = totalreserve_pages + MB2PAGES(16) +
	((useful_pages - MB2PAGES(16)) >> 1);
	else if (useful_pages < MB2PAGES(512))
	floor_pages = totalreserve_pages + MB2PAGES(40) +
	((useful_pages - MB2PAGES(40)) >> 3);
	else /* useful_pages >= MB2PAGES(512) */
	floor_pages = totalreserve_pages + MB2PAGES(99) +
	((useful_pages - MB2PAGES(99)) >> 5);
	if (tgt_pages < floor_pages)
	tgt_pages = floor_pages;
	balloon_set_new_target(tgt_pages +
	balloon_stats.current_pages - totalram_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);

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

	static ssize_t store_selfballoon_min_usable_mb(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_min_usable_mb = val;
	return count;
	}

	static SYSDEV_ATTR(selfballoon_min_usable_mb, S_IRUGO \| S_IWUSR,
	show_selfballoon_min_usable_mb,
	store_selfballoon_min_usable_mb);


	#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,
	&attr_selfballoon_min_usable_mb.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");