linux/drivers/xen/xen-selfballoon.c
Jana Saout d79d5959a0 xen: Add selfballoning memory reservation tunable.
Currently, the memory target in the Xen selfballooning driver is mainly
driven by the value of "Committed_AS".  However, there are cases in
which it is desirable to assign additional memory to be available for
the kernel, e.g. for local caches (which are not covered by cleancache),
e.g. dcache and inode caches.

This adds an additional tunable in the selfballooning driver (accessible
via sysfs) which allows the user to specify an additional constant
amount of memory to be reserved by the selfballoning driver for the
local domain.

Signed-off-by: Jana Saout <jana@saout.de>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2012-05-21 10:52:53 -04:00

577 lines
18 KiB
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. 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 <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;
/* 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 +
MB2PAGES(selfballoon_reserved_mb);
#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/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 = 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 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 = strict_strtoul(buf, 10, &val);
if (err || 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 = strict_strtoul(buf, 10, &val);
if (err || 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 = strict_strtoul(buf, 10, &val);
if (err || 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 = strict_strtoul(buf, 10, &val);
if (err || 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 = strict_strtoul(buf, 10, &val);
if (err || 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 = 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 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 = strict_strtoul(buf, 10, &val);
if (err || 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 = strict_strtoul(buf, 10, &val);
if (err || 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);
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");