2
0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-25 21:54:06 +08:00
linux-next/drivers/xen/xen-selfballoon.c
Greg Kroah-Hartman b24413180f License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier.  The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
 - file had no licensing information it it.
 - file was a */uapi/* one with no licensing information in it,
 - file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne.  Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed.  Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
 - Files considered eligible had to be source code files.
 - Make and config files were included as candidates if they contained >5
   lines of source
 - File already had some variant of a license header in it (even if <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-02 11:10:55 +01:00

580 lines
18 KiB
C

// SPDX-License-Identifier: GPL-2.0
/******************************************************************************
* 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);