/******************************************************************************
* 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 <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;
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");
