[mirror_ubuntu-artful-kernel.git] / drivers / xen / xen-selfballoon.c

/******************************************************************************
 * 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. Note, that selfballooning should be disabled by default
 * if frontswap is not configured.  Similarly selfballooning should be enabled
 * by default if frontswap is configured and can be disabled with the
 * "tmem.selfballooning=0" kernel boot option.  Finally, when frontswap is
 * configured, frontswap-selfshrinking can be disabled  with the
 * "tmem.selfshrink=0" kernel boot option.
 *
 * Selfballooning is disallowed in domain0 and force-disabled.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/bootmem.h>
#include <linux/swap.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/workqueue.h>
#include <linux/device.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;

/*
 * Amount of RAM in MB to add to the target number of pages.
 * Can be used to reserve some more room for caches and the like.
 */
static unsigned int selfballoon_reserved_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;

/*
 * 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;
	unsigned long last_frontswap_pages;
	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);
	frontswap_inertia_counter = frontswap_inertia;
}

#endif /* CONFIG_FRONTSWAP */

#define MB2PAGES(mb)	((mb) << (20 - PAGE_SHIFT))
#define PAGES2MB(pages) ((pages) >> (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 = vm_memory_committed() +
				totalreserve_pages +
				MB2PAGES(selfballoon_reserved_mb);
#ifdef CONFIG_FRONTSWAP
		/* allow space for frontswap pages to be repatriated */
		if (frontswap_selfshrinking)
			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_selfshrink();
		reset_timer = true;
	}
#endif
	if (reset_timer)
		schedule_delayed_work(&selfballoon_worker,
			selfballoon_interval * HZ);
}

#ifdef CONFIG_SYSFS

#include <linux/capability.h>

#define SELFBALLOON_SHOW(name, format, args...)				\
	static ssize_t show_##name(struct device *dev,	\
					  struct device_attribute *attr, \
					  char *buf) \
	{ \
		return sprintf(buf, format, ##args); \
	}

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

static ssize_t store_selfballooning(struct device *dev,
			    struct device_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 = kstrtoul(buf, 10, &tmp);
	if (err)
		return err;
	if ((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 DEVICE_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 device *dev,
					  struct device_attribute *attr,
					  const char *buf,
					  size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	selfballoon_interval = val;
	return count;
}

static DEVICE_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 device *dev,
					 struct device_attribute *attr,
					 const char *buf,
					 size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	selfballoon_downhysteresis = val;
	return count;
}

static DEVICE_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 device *dev,
				       struct device_attribute *attr,
				       const char *buf,
				       size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	selfballoon_uphysteresis = val;
	return count;
}

static DEVICE_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 device *dev,
					       struct device_attribute *attr,
					       const char *buf,
					       size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	selfballoon_min_usable_mb = val;
	return count;
}

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

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

static ssize_t store_selfballoon_reserved_mb(struct device *dev,
					     struct device_attribute *attr,
					     const char *buf,
					     size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	selfballoon_reserved_mb = val;
	return count;
}

static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
		   show_selfballoon_reserved_mb,
		   store_selfballoon_reserved_mb);


#ifdef CONFIG_FRONTSWAP
SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);

static ssize_t store_frontswap_selfshrinking(struct device *dev,
					     struct device_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 = kstrtoul(buf, 10, &tmp);
	if (err)
		return err;
	if ((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 DEVICE_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 device *dev,
				       struct device_attribute *attr,
				       const char *buf,
				       size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	frontswap_inertia = val;
	frontswap_inertia_counter = val;
	return count;
}

static DEVICE_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 device *dev,
					  struct device_attribute *attr,
					  const char *buf,
					  size_t count)
{
	unsigned long val;
	int err;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	err = kstrtoul(buf, 10, &val);
	if (err)
		return err;
	if (val == 0)
		return -EINVAL;
	frontswap_hysteresis = val;
	return count;
}

static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
		   show_frontswap_hysteresis, store_frontswap_hysteresis);

#endif /* CONFIG_FRONTSWAP */

static struct attribute *selfballoon_attrs[] = {
	&dev_attr_selfballooning.attr,
	&dev_attr_selfballoon_interval.attr,
	&dev_attr_selfballoon_downhysteresis.attr,
	&dev_attr_selfballoon_uphysteresis.attr,
	&dev_attr_selfballoon_min_usable_mb.attr,
	&dev_attr_selfballoon_reserved_mb.attr,
#ifdef CONFIG_FRONTSWAP
	&dev_attr_frontswap_selfshrinking.attr,
	&dev_attr_frontswap_hysteresis.attr,
	&dev_attr_frontswap_inertia.attr,
#endif
	NULL
};

static const struct attribute_group selfballoon_group = {
	.name = "selfballoon",
	.attrs = selfballoon_attrs
};
#endif

int register_xen_selfballooning(struct device *dev)
{
	int error = -1;

#ifdef CONFIG_SYSFS
	error = sysfs_create_group(&dev->kobj, &selfballoon_group);
#endif
	return error;
}
EXPORT_SYMBOL(register_xen_selfballooning);

int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
{
	bool enable = false;
	unsigned long reserve_pages;

	if (!xen_domain())
		return -ENODEV;

	if (xen_initial_domain()) {
		pr_info("Xen selfballooning driver disabled for domain0\n");
		return -ENODEV;
	}

	xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
	if (xen_selfballooning_enabled) {
		pr_info("Initializing Xen selfballooning driver\n");
		enable = true;
	}
#ifdef CONFIG_FRONTSWAP
	frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
	if (frontswap_selfshrinking) {
		pr_info("Initializing frontswap selfshrinking driver\n");
		enable = true;
	}
#endif
	if (!enable)
		return -ENODEV;

	/*
	 * Give selfballoon_reserved_mb a default value(10% of total ram pages)
	 * to make selfballoon not so aggressive.
	 *
	 * There are mainly two reasons:
	 * 1) The original goal_page didn't consider some pages used by kernel
	 *    space, like slab pages and memory used by device drivers.
	 *
	 * 2) The balloon driver may not give back memory to guest OS fast
	 *    enough when the workload suddenly aquries a lot of physical memory.
	 *
	 * In both cases, the guest OS will suffer from memory pressure and
	 * OOM killer may be triggered.
	 * By reserving extra 10% of total ram pages, we can keep the system
	 * much more reliably and response faster in some cases.
	 */
	if (!selfballoon_reserved_mb) {
		reserve_pages = totalram_pages / 10;
		selfballoon_reserved_mb = PAGES2MB(reserve_pages);
	}
	schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);

	return 0;
}
EXPORT_SYMBOL(xen_selfballoon_init);
Commit	Line	Data
a50777c7 DM	1	/******************************************************************************
	2	* Xen selfballoon driver (and optional frontswap self-shrinking driver)
	3	*
	4	* Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.
	5	*
	6	* This code complements the cleancache and frontswap patchsets to optimize
	7	* support for Xen Transcendent Memory ("tmem"). The policy it implements
	8	* is rudimentary and will likely improve over time, but it does work well
	9	* enough today.
	10	*
	11	* Two functionalities are implemented here which both use "control theory"
	12	* (feedback) to optimize memory utilization. In a virtualized environment
	13	* such as Xen, RAM is often a scarce resource and we would like to ensure
	14	* that each of a possibly large number of virtual machines is using RAM
	15	* efficiently, i.e. using as little as possible when under light load
	16	* and obtaining as much as possible when memory demands are high.
	17	* Since RAM needs vary highly dynamically and sometimes dramatically,
	18	* "hysteresis" is used, that is, memory target is determined not just
	19	* on current data but also on past data stored in the system.
	20	*
	21	* "Selfballooning" creates memory pressure by managing the Xen balloon
	22	* driver to decrease and increase available kernel memory, driven
	23	* largely by the target value of "Committed_AS" (see /proc/meminfo).
	24	* Since Committed_AS does not account for clean mapped pages (i.e. pages
	25	* in RAM that are identical to pages on disk), selfballooning has the
	26	* affect of pushing less frequently used clean pagecache pages out of
	27	* kernel RAM and, presumably using cleancache, into Xen tmem where
	28	* Xen can more efficiently optimize RAM utilization for such pages.
	29	*
	30	* When kernel memory demand unexpectedly increases faster than Xen, via
	31	* the selfballoon driver, is able to (or chooses to) provide usable RAM,
	32	* the kernel may invoke swapping. In most cases, frontswap is able
	33	* to absorb this swapping into Xen tmem. However, due to the fact
	34	* that the kernel swap subsystem assumes swapping occurs to a disk,
	35	* swapped pages may sit on the disk for a very long time; even if
	36	* the kernel knows the page will never be used again. This is because
	37	* the disk space costs very little and can be overwritten when
	38	* necessary. When such stale pages are in frontswap, however, they
	39	* are taking up valuable real estate. "Frontswap selfshrinking" works
	40	* to resolve this: When frontswap activity is otherwise stable
	41	* and the guest kernel is not under memory pressure, the "frontswap
	42	* selfshrinking" accounts for this by providing pressure to remove some
	43	* pages from frontswap and return them to kernel memory.
	44	*
	45	* For both "selfballooning" and "frontswap-selfshrinking", a worker
	46	* thread is used and sysfs tunables are provided to adjust the frequency
	47	* and rate of adjustments to achieve the goal, as well as to disable one
	48	* or both functions independently.
	49	*
	50	* While some argue that this functionality can and should be implemented
	51	* in userspace, it has been observed that bad things happen (e.g. OOMs).
	52	*
	53	* System configuration note: Selfballooning should not be enabled on
	54	* systems without a sufficiently large swap device configured; for best
	55	* results, it is recommended that total swap be increased by the size
37d46e15 KRW	56	* of the guest memory. Note, that selfballooning should be disabled by default
	57	* if frontswap is not configured. Similarly selfballooning should be enabled
	58	* by default if frontswap is configured and can be disabled with the
	59	* "tmem.selfballooning=0" kernel boot option. Finally, when frontswap is
	60	* configured, frontswap-selfshrinking can be disabled with the
	61	* "tmem.selfshrink=0" kernel boot option.
a50777c7 DM	62	*
	63	* Selfballooning is disallowed in domain0 and force-disabled.
	64	*
	65	*/
	66
283c0972 JP	67	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
283c0972 JP	68
a50777c7	69	#include <linux/kernel.h>
38a1ed4f DM	70	#include <linux/bootmem.h>
38a1ed4f DM	71	#include <linux/swap.h>
a50777c7 DM	72	#include <linux/mm.h>
a50777c7 DM	73	#include <linux/mman.h>
0642d2ed	74	#include <linux/workqueue.h>
cb0c05c5	75	#include <linux/device.h>
a50777c7	76	#include <xen/balloon.h>
a50777c7	77	#include <xen/tmem.h>
0642d2ed	78	#include <xen/xen.h>
a50777c7 DM	79
	80	/* Enable/disable with sysfs. */
	81	static int xen_selfballooning_enabled __read_mostly;
	82
	83	/*
	84	* Controls rate at which memory target (this iteration) approaches
	85	* ultimate goal when memory need is increasing (up-hysteresis) or
	86	* decreasing (down-hysteresis). Higher values of hysteresis cause
	87	* slower increases/decreases. The default values for the various
	88	* parameters were deemed reasonable by experimentation, may be
	89	* workload-dependent, and can all be adjusted via sysfs.
	90	*/
	91	static unsigned int selfballoon_downhysteresis __read_mostly = 8;
	92	static unsigned int selfballoon_uphysteresis __read_mostly = 1;
	93
	94	/* In HZ, controls frequency of worker invocation. */
	95	static unsigned int selfballoon_interval __read_mostly = 5;
	96
38a1ed4f DM	97	/*
	98	* Minimum usable RAM in MB for selfballooning target for balloon.
	99	* If non-zero, it is added to totalreserve_pages and self-ballooning
	100	* will not balloon below the sum. If zero, a piecewise linear function
	101	* is calculated as a minimum and added to totalreserve_pages. Note that
	102	* setting this value indiscriminately may cause OOMs and crashes.
	103	*/
	104	static unsigned int selfballoon_min_usable_mb;
	105
d79d5959 JS	106	/*
	107	* Amount of RAM in MB to add to the target number of pages.
	108	* Can be used to reserve some more room for caches and the like.
	109	*/
	110	static unsigned int selfballoon_reserved_mb;
	111
a50777c7 DM	112	static void selfballoon_process(struct work_struct *work);
	113	static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
	114
	115	#ifdef CONFIG_FRONTSWAP
	116	#include <linux/frontswap.h>
	117
	118	/* Enable/disable with sysfs. */
	119	static bool frontswap_selfshrinking __read_mostly;
	120
a50777c7 DM	121	/*
	122	* The default values for the following parameters were deemed reasonable
	123	* by experimentation, may be workload-dependent, and can all be
	124	* adjusted via sysfs.
	125	*/
	126
	127	/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
	128	static unsigned int frontswap_hysteresis __read_mostly = 20;
	129
	130	/*
	131	* Number of selfballoon worker invocations to wait before observing that
	132	* frontswap selfshrinking should commence. Note that selfshrinking does
	133	* not use a separate worker thread.
	134	*/
	135	static unsigned int frontswap_inertia __read_mostly = 3;
	136
	137	/* Countdown to next invocation of frontswap_shrink() */
	138	static unsigned long frontswap_inertia_counter;
	139
	140	/*
	141	* Invoked by the selfballoon worker thread, uses current number of pages
	142	* in frontswap (frontswap_curr_pages()), previous status, and control
	143	* values (hysteresis and inertia) to determine if frontswap should be
	144	* shrunk and what the new frontswap size should be. Note that
	145	* frontswap_shrink is essentially a partial swapoff that immediately
	146	* transfers pages from the "swap device" (frontswap) back into kernel
	147	* RAM; despite the name, frontswap "shrinking" is very different from
	148	* the "shrinker" interface used by the kernel MM subsystem to reclaim
	149	* memory.
	150	*/
	151	static void frontswap_selfshrink(void)
	152	{
	153	static unsigned long cur_frontswap_pages;
03993730 GS	154	unsigned long last_frontswap_pages;
03993730 GS	155	unsigned long tgt_frontswap_pages;
a50777c7 DM	156
	157	last_frontswap_pages = cur_frontswap_pages;
	158	cur_frontswap_pages = frontswap_curr_pages();
	159	if (!cur_frontswap_pages \|\|
	160	(cur_frontswap_pages > last_frontswap_pages)) {
	161	frontswap_inertia_counter = frontswap_inertia;
	162	return;
	163	}
	164	if (frontswap_inertia_counter && --frontswap_inertia_counter)
	165	return;
	166	if (cur_frontswap_pages <= frontswap_hysteresis)
	167	tgt_frontswap_pages = 0;
	168	else
	169	tgt_frontswap_pages = cur_frontswap_pages -
	170	(cur_frontswap_pages / frontswap_hysteresis);
	171	frontswap_shrink(tgt_frontswap_pages);
d4c7abdf	172	frontswap_inertia_counter = frontswap_inertia;
a50777c7 DM	173	}
a50777c7 DM	174
a50777c7 DM	175	#endif /* CONFIG_FRONTSWAP */
a50777c7 DM	176
38a1ed4f	177	#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
bc1b0df5	178	#define PAGES2MB(pages) ((pages) >> (20 - PAGE_SHIFT))
38a1ed4f	179
a50777c7 DM	180	/*
	181	* Use current balloon size, the goal (vm_committed_as), and hysteresis
	182	* parameters to set a new target balloon size
	183	*/
	184	static void selfballoon_process(struct work_struct *work)
	185	{
38a1ed4f DM	186	unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
38a1ed4f DM	187	unsigned long useful_pages;
a50777c7 DM	188	bool reset_timer = false;
	189
	190	if (xen_selfballooning_enabled) {
38a1ed4f	191	cur_pages = totalram_pages;
a50777c7	192	tgt_pages = cur_pages; /* default is no change */
997071bc	193	goal_pages = vm_memory_committed() +
d79d5959 JS	194	totalreserve_pages +
d79d5959 JS	195	MB2PAGES(selfballoon_reserved_mb);
a50777c7 DM	196	#ifdef CONFIG_FRONTSWAP
a50777c7 DM	197	/* allow space for frontswap pages to be repatriated */
8ea1d2a1	198	if (frontswap_selfshrinking)
a50777c7 DM	199	goal_pages += frontswap_curr_pages();
	200	#endif
	201	if (cur_pages > goal_pages)
	202	tgt_pages = cur_pages -
	203	((cur_pages - goal_pages) /
	204	selfballoon_downhysteresis);
	205	else if (cur_pages < goal_pages)
	206	tgt_pages = cur_pages +
	207	((goal_pages - cur_pages) /
	208	selfballoon_uphysteresis);
	209	/* else if cur_pages == goal_pages, no change */
38a1ed4f DM	210	useful_pages = max_pfn - totalreserve_pages;
	211	if (selfballoon_min_usable_mb != 0)
	212	floor_pages = totalreserve_pages +
	213	MB2PAGES(selfballoon_min_usable_mb);
	214	/* piecewise linear function ending in ~3% slope */
	215	else if (useful_pages < MB2PAGES(16))
	216	floor_pages = max_pfn; /* not worth ballooning */
	217	else if (useful_pages < MB2PAGES(64))
	218	floor_pages = totalreserve_pages + MB2PAGES(16) +
	219	((useful_pages - MB2PAGES(16)) >> 1);
	220	else if (useful_pages < MB2PAGES(512))
	221	floor_pages = totalreserve_pages + MB2PAGES(40) +
	222	((useful_pages - MB2PAGES(40)) >> 3);
	223	else /* useful_pages >= MB2PAGES(512) */
	224	floor_pages = totalreserve_pages + MB2PAGES(99) +
	225	((useful_pages - MB2PAGES(99)) >> 5);
	226	if (tgt_pages < floor_pages)
	227	tgt_pages = floor_pages;
	228	balloon_set_new_target(tgt_pages +
	229	balloon_stats.current_pages - totalram_pages);
a50777c7 DM	230	reset_timer = true;
	231	}
	232	#ifdef CONFIG_FRONTSWAP
8ea1d2a1	233	if (frontswap_selfshrinking) {
a50777c7 DM	234	frontswap_selfshrink();
	235	reset_timer = true;
	236	}
	237	#endif
	238	if (reset_timer)
	239	schedule_delayed_work(&selfballoon_worker,
	240	selfballoon_interval * HZ);
	241	}
	242
	243	#ifdef CONFIG_SYSFS
	244
a50777c7 DM	245	#include <linux/capability.h>
	246
	247	#define SELFBALLOON_SHOW(name, format, args...) \
07068021 KS	248	static ssize_t show_##name(struct device *dev, \
	249	struct device_attribute *attr, \
	250	char *buf) \
a50777c7 DM	251	{ \
	252	return sprintf(buf, format, ##args); \
	253	}
	254
	255	SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
	256
07068021 KS	257	static ssize_t store_selfballooning(struct device *dev,
07068021 KS	258	struct device_attribute *attr,
a50777c7 DM	259	const char *buf,
	260	size_t count)
	261	{
	262	bool was_enabled = xen_selfballooning_enabled;
	263	unsigned long tmp;
	264	int err;
	265
	266	if (!capable(CAP_SYS_ADMIN))
	267	return -EPERM;
	268
d3dbd93d JH	269	err = kstrtoul(buf, 10, &tmp);
	270	if (err)
	271	return err;
	272	if ((tmp != 0) && (tmp != 1))
a50777c7 DM	273	return -EINVAL;
	274
	275	xen_selfballooning_enabled = !!tmp;
	276	if (!was_enabled && xen_selfballooning_enabled)
	277	schedule_delayed_work(&selfballoon_worker,
	278	selfballoon_interval * HZ);
	279
	280	return count;
	281	}
	282
07068021	283	static DEVICE_ATTR(selfballooning, S_IRUGO \| S_IWUSR,
a50777c7 DM	284	show_selfballooning, store_selfballooning);
	285
	286	SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
	287
07068021 KS	288	static ssize_t store_selfballoon_interval(struct device *dev,
07068021 KS	289	struct device_attribute *attr,
a50777c7 DM	290	const char *buf,
	291	size_t count)
	292	{
	293	unsigned long val;
	294	int err;
	295
	296	if (!capable(CAP_SYS_ADMIN))
	297	return -EPERM;
d3dbd93d JH	298	err = kstrtoul(buf, 10, &val);
	299	if (err)
	300	return err;
	301	if (val == 0)
a50777c7 DM	302	return -EINVAL;
	303	selfballoon_interval = val;
	304	return count;
	305	}
	306
07068021	307	static DEVICE_ATTR(selfballoon_interval, S_IRUGO \| S_IWUSR,
a50777c7 DM	308	show_selfballoon_interval, store_selfballoon_interval);
	309
	310	SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
	311
07068021 KS	312	static ssize_t store_selfballoon_downhys(struct device *dev,
07068021 KS	313	struct device_attribute *attr,
a50777c7 DM	314	const char *buf,
	315	size_t count)
	316	{
	317	unsigned long val;
	318	int err;
	319
	320	if (!capable(CAP_SYS_ADMIN))
	321	return -EPERM;
d3dbd93d JH	322	err = kstrtoul(buf, 10, &val);
	323	if (err)
	324	return err;
	325	if (val == 0)
a50777c7 DM	326	return -EINVAL;
	327	selfballoon_downhysteresis = val;
	328	return count;
	329	}
	330
07068021	331	static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO \| S_IWUSR,
a50777c7 DM	332	show_selfballoon_downhys, store_selfballoon_downhys);
	333
	334
	335	SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
	336
07068021 KS	337	static ssize_t store_selfballoon_uphys(struct device *dev,
07068021 KS	338	struct device_attribute *attr,
a50777c7 DM	339	const char *buf,
	340	size_t count)
	341	{
	342	unsigned long val;
	343	int err;
	344
	345	if (!capable(CAP_SYS_ADMIN))
	346	return -EPERM;
d3dbd93d JH	347	err = kstrtoul(buf, 10, &val);
	348	if (err)
	349	return err;
	350	if (val == 0)
a50777c7 DM	351	return -EINVAL;
	352	selfballoon_uphysteresis = val;
	353	return count;
	354	}
	355
07068021	356	static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO \| S_IWUSR,
a50777c7 DM	357	show_selfballoon_uphys, store_selfballoon_uphys);
a50777c7 DM	358
38a1ed4f DM	359	SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
	360	selfballoon_min_usable_mb);
	361
07068021 KS	362	static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
07068021 KS	363	struct device_attribute *attr,
38a1ed4f DM	364	const char *buf,
	365	size_t count)
	366	{
	367	unsigned long val;
	368	int err;
	369
	370	if (!capable(CAP_SYS_ADMIN))
	371	return -EPERM;
d3dbd93d JH	372	err = kstrtoul(buf, 10, &val);
	373	if (err)
	374	return err;
	375	if (val == 0)
38a1ed4f DM	376	return -EINVAL;
	377	selfballoon_min_usable_mb = val;
	378	return count;
	379	}
	380
07068021	381	static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO \| S_IWUSR,
38a1ed4f DM	382	show_selfballoon_min_usable_mb,
	383	store_selfballoon_min_usable_mb);
	384
d79d5959 JS	385	SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
	386	selfballoon_reserved_mb);
	387
	388	static ssize_t store_selfballoon_reserved_mb(struct device *dev,
	389	struct device_attribute *attr,
	390	const char *buf,
	391	size_t count)
	392	{
	393	unsigned long val;
	394	int err;
	395
	396	if (!capable(CAP_SYS_ADMIN))
	397	return -EPERM;
d3dbd93d JH	398	err = kstrtoul(buf, 10, &val);
	399	if (err)
	400	return err;
	401	if (val == 0)
d79d5959 JS	402	return -EINVAL;
	403	selfballoon_reserved_mb = val;
	404	return count;
	405	}
	406
	407	static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO \| S_IWUSR,
	408	show_selfballoon_reserved_mb,
	409	store_selfballoon_reserved_mb);
	410
38a1ed4f	411
a50777c7 DM	412	#ifdef CONFIG_FRONTSWAP
	413	SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
	414
07068021 KS	415	static ssize_t store_frontswap_selfshrinking(struct device *dev,
07068021 KS	416	struct device_attribute *attr,
a50777c7 DM	417	const char *buf,
	418	size_t count)
	419	{
	420	bool was_enabled = frontswap_selfshrinking;
	421	unsigned long tmp;
	422	int err;
	423
	424	if (!capable(CAP_SYS_ADMIN))
	425	return -EPERM;
d3dbd93d JH	426	err = kstrtoul(buf, 10, &tmp);
	427	if (err)
	428	return err;
	429	if ((tmp != 0) && (tmp != 1))
a50777c7 DM	430	return -EINVAL;
	431	frontswap_selfshrinking = !!tmp;
	432	if (!was_enabled && !xen_selfballooning_enabled &&
	433	frontswap_selfshrinking)
	434	schedule_delayed_work(&selfballoon_worker,
	435	selfballoon_interval * HZ);
	436
	437	return count;
	438	}
	439
07068021	440	static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO \| S_IWUSR,
a50777c7 DM	441	show_frontswap_selfshrinking, store_frontswap_selfshrinking);
	442
	443	SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
	444
07068021 KS	445	static ssize_t store_frontswap_inertia(struct device *dev,
07068021 KS	446	struct device_attribute *attr,
a50777c7 DM	447	const char *buf,
	448	size_t count)
	449	{
	450	unsigned long val;
	451	int err;
	452
	453	if (!capable(CAP_SYS_ADMIN))
	454	return -EPERM;
d3dbd93d JH	455	err = kstrtoul(buf, 10, &val);
	456	if (err)
	457	return err;
	458	if (val == 0)
a50777c7 DM	459	return -EINVAL;
	460	frontswap_inertia = val;
	461	frontswap_inertia_counter = val;
	462	return count;
	463	}
	464
07068021	465	static DEVICE_ATTR(frontswap_inertia, S_IRUGO \| S_IWUSR,
a50777c7 DM	466	show_frontswap_inertia, store_frontswap_inertia);
	467
	468	SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
	469
07068021 KS	470	static ssize_t store_frontswap_hysteresis(struct device *dev,
07068021 KS	471	struct device_attribute *attr,
a50777c7 DM	472	const char *buf,
	473	size_t count)
	474	{
	475	unsigned long val;
	476	int err;
	477
	478	if (!capable(CAP_SYS_ADMIN))
	479	return -EPERM;
d3dbd93d JH	480	err = kstrtoul(buf, 10, &val);
	481	if (err)
	482	return err;
	483	if (val == 0)
a50777c7 DM	484	return -EINVAL;
	485	frontswap_hysteresis = val;
	486	return count;
	487	}
	488
07068021	489	static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO \| S_IWUSR,
a50777c7 DM	490	show_frontswap_hysteresis, store_frontswap_hysteresis);
	491
	492	#endif /* CONFIG_FRONTSWAP */
	493
	494	static struct attribute *selfballoon_attrs[] = {
07068021 KS	495	&dev_attr_selfballooning.attr,
	496	&dev_attr_selfballoon_interval.attr,
	497	&dev_attr_selfballoon_downhysteresis.attr,
	498	&dev_attr_selfballoon_uphysteresis.attr,
	499	&dev_attr_selfballoon_min_usable_mb.attr,
d79d5959	500	&dev_attr_selfballoon_reserved_mb.attr,
a50777c7	501	#ifdef CONFIG_FRONTSWAP
07068021 KS	502	&dev_attr_frontswap_selfshrinking.attr,
	503	&dev_attr_frontswap_hysteresis.attr,
	504	&dev_attr_frontswap_inertia.attr,
a50777c7 DM	505	#endif
	506	NULL
	507	};
	508
ead1d014	509	static const struct attribute_group selfballoon_group = {
a50777c7 DM	510	.name = "selfballoon",
	511	.attrs = selfballoon_attrs
	512	};
	513	#endif
	514
07068021	515	int register_xen_selfballooning(struct device *dev)
a50777c7 DM	516	{
	517	int error = -1;
	518
	519	#ifdef CONFIG_SYSFS
07068021	520	error = sysfs_create_group(&dev->kobj, &selfballoon_group);
a50777c7 DM	521	#endif
	522	return error;
	523	}
	524	EXPORT_SYMBOL(register_xen_selfballooning);
	525
10a7a077	526	int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
a50777c7 DM	527	{
a50777c7 DM	528	bool enable = false;
bc1b0df5	529	unsigned long reserve_pages;
a50777c7 DM	530
	531	if (!xen_domain())
	532	return -ENODEV;
	533
	534	if (xen_initial_domain()) {
283c0972	535	pr_info("Xen selfballooning driver disabled for domain0\n");
a50777c7 DM	536	return -ENODEV;
	537	}
	538
	539	xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
	540	if (xen_selfballooning_enabled) {
283c0972	541	pr_info("Initializing Xen selfballooning driver\n");
a50777c7 DM	542	enable = true;
	543	}
	544	#ifdef CONFIG_FRONTSWAP
	545	frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
	546	if (frontswap_selfshrinking) {
283c0972	547	pr_info("Initializing frontswap selfshrinking driver\n");
a50777c7 DM	548	enable = true;
	549	}
	550	#endif
	551	if (!enable)
	552	return -ENODEV;
	553
bc1b0df5 BL	554	/*
	555	* Give selfballoon_reserved_mb a default value(10% of total ram pages)
	556	* to make selfballoon not so aggressive.
	557	*
	558	* There are mainly two reasons:
	559	* 1) The original goal_page didn't consider some pages used by kernel
	560	* space, like slab pages and memory used by device drivers.
	561	*
	562	* 2) The balloon driver may not give back memory to guest OS fast
	563	* enough when the workload suddenly aquries a lot of physical memory.
	564	*
	565	* In both cases, the guest OS will suffer from memory pressure and
	566	* OOM killer may be triggered.
	567	* By reserving extra 10% of total ram pages, we can keep the system
	568	* much more reliably and response faster in some cases.
	569	*/
	570	if (!selfballoon_reserved_mb) {
	571	reserve_pages = totalram_pages / 10;
	572	selfballoon_reserved_mb = PAGES2MB(reserve_pages);
	573	}
a50777c7 DM	574	schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
	575
	576	return 0;
	577	}
10a7a077	578	EXPORT_SYMBOL(xen_selfballoon_init);