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Dan Magenheimera50777c2011-07-08 12:26:21 -06001/******************************************************************************
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
56 * of the guest memory. Also, while technically not required to be
57 * configured, it is highly recommended that frontswap also be configured
58 * and enabled when selfballooning is running. So, selfballooning
59 * is disabled by default if frontswap is not configured and can only
60 * be enabled with the "selfballooning" kernel boot option; similarly
61 * selfballooning is enabled by default if frontswap is configured and
62 * can be disabled with the "noselfballooning" kernel boot option. Finally,
63 * when frontswap is configured, frontswap-selfshrinking can be disabled
64 * with the "noselfshrink" kernel boot option.
65 *
66 * Selfballooning is disallowed in domain0 and force-disabled.
67 *
68 */
69
70#include <linux/kernel.h>
Dan Magenheimer38a1ed42011-09-27 08:47:58 -060071#include <linux/bootmem.h>
72#include <linux/swap.h>
Dan Magenheimera50777c2011-07-08 12:26:21 -060073#include <linux/mm.h>
74#include <linux/mman.h>
Randy Dunlap4fec0e02011-08-15 21:41:43 -070075#include <linux/module.h>
Konrad Rzeszutek Wilk0642d2e2011-07-22 14:01:16 -040076#include <linux/workqueue.h>
Greg Kroah-Hartmancb0c05c2011-12-15 11:07:02 -080077#include <linux/device.h>
Dan Magenheimera50777c2011-07-08 12:26:21 -060078#include <xen/balloon.h>
Dan Magenheimera50777c2011-07-08 12:26:21 -060079#include <xen/tmem.h>
Konrad Rzeszutek Wilk0642d2e2011-07-22 14:01:16 -040080#include <xen/xen.h>
Dan Magenheimera50777c2011-07-08 12:26:21 -060081
82/* Enable/disable with sysfs. */
83static int xen_selfballooning_enabled __read_mostly;
84
85/*
86 * Controls rate at which memory target (this iteration) approaches
87 * ultimate goal when memory need is increasing (up-hysteresis) or
88 * decreasing (down-hysteresis). Higher values of hysteresis cause
89 * slower increases/decreases. The default values for the various
90 * parameters were deemed reasonable by experimentation, may be
91 * workload-dependent, and can all be adjusted via sysfs.
92 */
93static unsigned int selfballoon_downhysteresis __read_mostly = 8;
94static unsigned int selfballoon_uphysteresis __read_mostly = 1;
95
96/* In HZ, controls frequency of worker invocation. */
97static unsigned int selfballoon_interval __read_mostly = 5;
98
Dan Magenheimer38a1ed42011-09-27 08:47:58 -060099/*
100 * Minimum usable RAM in MB for selfballooning target for balloon.
101 * If non-zero, it is added to totalreserve_pages and self-ballooning
102 * will not balloon below the sum. If zero, a piecewise linear function
103 * is calculated as a minimum and added to totalreserve_pages. Note that
104 * setting this value indiscriminately may cause OOMs and crashes.
105 */
106static unsigned int selfballoon_min_usable_mb;
107
Dan Magenheimera50777c2011-07-08 12:26:21 -0600108static void selfballoon_process(struct work_struct *work);
109static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
110
111#ifdef CONFIG_FRONTSWAP
112#include <linux/frontswap.h>
113
114/* Enable/disable with sysfs. */
115static bool frontswap_selfshrinking __read_mostly;
116
117/* Enable/disable with kernel boot option. */
118static bool use_frontswap_selfshrink __initdata = true;
119
120/*
121 * The default values for the following parameters were deemed reasonable
122 * by experimentation, may be workload-dependent, and can all be
123 * adjusted via sysfs.
124 */
125
126/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
127static unsigned int frontswap_hysteresis __read_mostly = 20;
128
129/*
130 * Number of selfballoon worker invocations to wait before observing that
131 * frontswap selfshrinking should commence. Note that selfshrinking does
132 * not use a separate worker thread.
133 */
134static unsigned int frontswap_inertia __read_mostly = 3;
135
136/* Countdown to next invocation of frontswap_shrink() */
137static unsigned long frontswap_inertia_counter;
138
139/*
140 * Invoked by the selfballoon worker thread, uses current number of pages
141 * in frontswap (frontswap_curr_pages()), previous status, and control
142 * values (hysteresis and inertia) to determine if frontswap should be
143 * shrunk and what the new frontswap size should be. Note that
144 * frontswap_shrink is essentially a partial swapoff that immediately
145 * transfers pages from the "swap device" (frontswap) back into kernel
146 * RAM; despite the name, frontswap "shrinking" is very different from
147 * the "shrinker" interface used by the kernel MM subsystem to reclaim
148 * memory.
149 */
150static void frontswap_selfshrink(void)
151{
152 static unsigned long cur_frontswap_pages;
153 static unsigned long last_frontswap_pages;
154 static unsigned long tgt_frontswap_pages;
155
156 last_frontswap_pages = cur_frontswap_pages;
157 cur_frontswap_pages = frontswap_curr_pages();
158 if (!cur_frontswap_pages ||
159 (cur_frontswap_pages > last_frontswap_pages)) {
160 frontswap_inertia_counter = frontswap_inertia;
161 return;
162 }
163 if (frontswap_inertia_counter && --frontswap_inertia_counter)
164 return;
165 if (cur_frontswap_pages <= frontswap_hysteresis)
166 tgt_frontswap_pages = 0;
167 else
168 tgt_frontswap_pages = cur_frontswap_pages -
169 (cur_frontswap_pages / frontswap_hysteresis);
170 frontswap_shrink(tgt_frontswap_pages);
171}
172
173static int __init xen_nofrontswap_selfshrink_setup(char *s)
174{
175 use_frontswap_selfshrink = false;
176 return 1;
177}
178
179__setup("noselfshrink", xen_nofrontswap_selfshrink_setup);
180
181/* Disable with kernel boot option. */
182static bool use_selfballooning __initdata = true;
183
184static int __init xen_noselfballooning_setup(char *s)
185{
186 use_selfballooning = false;
187 return 1;
188}
189
190__setup("noselfballooning", xen_noselfballooning_setup);
191#else /* !CONFIG_FRONTSWAP */
192/* Enable with kernel boot option. */
193static bool use_selfballooning __initdata = false;
194
195static int __init xen_selfballooning_setup(char *s)
196{
197 use_selfballooning = true;
198 return 1;
199}
200
201__setup("selfballooning", xen_selfballooning_setup);
202#endif /* CONFIG_FRONTSWAP */
203
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600204#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
205
Dan Magenheimera50777c2011-07-08 12:26:21 -0600206/*
207 * Use current balloon size, the goal (vm_committed_as), and hysteresis
208 * parameters to set a new target balloon size
209 */
210static void selfballoon_process(struct work_struct *work)
211{
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600212 unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
213 unsigned long useful_pages;
Dan Magenheimera50777c2011-07-08 12:26:21 -0600214 bool reset_timer = false;
215
216 if (xen_selfballooning_enabled) {
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600217 cur_pages = totalram_pages;
Dan Magenheimera50777c2011-07-08 12:26:21 -0600218 tgt_pages = cur_pages; /* default is no change */
219 goal_pages = percpu_counter_read_positive(&vm_committed_as) +
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600220 totalreserve_pages;
Dan Magenheimera50777c2011-07-08 12:26:21 -0600221#ifdef CONFIG_FRONTSWAP
222 /* allow space for frontswap pages to be repatriated */
223 if (frontswap_selfshrinking && frontswap_enabled)
224 goal_pages += frontswap_curr_pages();
225#endif
226 if (cur_pages > goal_pages)
227 tgt_pages = cur_pages -
228 ((cur_pages - goal_pages) /
229 selfballoon_downhysteresis);
230 else if (cur_pages < goal_pages)
231 tgt_pages = cur_pages +
232 ((goal_pages - cur_pages) /
233 selfballoon_uphysteresis);
234 /* else if cur_pages == goal_pages, no change */
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600235 useful_pages = max_pfn - totalreserve_pages;
236 if (selfballoon_min_usable_mb != 0)
237 floor_pages = totalreserve_pages +
238 MB2PAGES(selfballoon_min_usable_mb);
239 /* piecewise linear function ending in ~3% slope */
240 else if (useful_pages < MB2PAGES(16))
241 floor_pages = max_pfn; /* not worth ballooning */
242 else if (useful_pages < MB2PAGES(64))
243 floor_pages = totalreserve_pages + MB2PAGES(16) +
244 ((useful_pages - MB2PAGES(16)) >> 1);
245 else if (useful_pages < MB2PAGES(512))
246 floor_pages = totalreserve_pages + MB2PAGES(40) +
247 ((useful_pages - MB2PAGES(40)) >> 3);
248 else /* useful_pages >= MB2PAGES(512) */
249 floor_pages = totalreserve_pages + MB2PAGES(99) +
250 ((useful_pages - MB2PAGES(99)) >> 5);
251 if (tgt_pages < floor_pages)
252 tgt_pages = floor_pages;
253 balloon_set_new_target(tgt_pages +
254 balloon_stats.current_pages - totalram_pages);
Dan Magenheimera50777c2011-07-08 12:26:21 -0600255 reset_timer = true;
256 }
257#ifdef CONFIG_FRONTSWAP
258 if (frontswap_selfshrinking && frontswap_enabled) {
259 frontswap_selfshrink();
260 reset_timer = true;
261 }
262#endif
263 if (reset_timer)
264 schedule_delayed_work(&selfballoon_worker,
265 selfballoon_interval * HZ);
266}
267
268#ifdef CONFIG_SYSFS
269
Dan Magenheimera50777c2011-07-08 12:26:21 -0600270#include <linux/capability.h>
271
272#define SELFBALLOON_SHOW(name, format, args...) \
Kay Sievers07068022011-12-14 15:32:50 -0800273 static ssize_t show_##name(struct device *dev, \
274 struct device_attribute *attr, \
275 char *buf) \
Dan Magenheimera50777c2011-07-08 12:26:21 -0600276 { \
277 return sprintf(buf, format, ##args); \
278 }
279
280SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
281
Kay Sievers07068022011-12-14 15:32:50 -0800282static ssize_t store_selfballooning(struct device *dev,
283 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600284 const char *buf,
285 size_t count)
286{
287 bool was_enabled = xen_selfballooning_enabled;
288 unsigned long tmp;
289 int err;
290
291 if (!capable(CAP_SYS_ADMIN))
292 return -EPERM;
293
294 err = strict_strtoul(buf, 10, &tmp);
295 if (err || ((tmp != 0) && (tmp != 1)))
296 return -EINVAL;
297
298 xen_selfballooning_enabled = !!tmp;
299 if (!was_enabled && xen_selfballooning_enabled)
300 schedule_delayed_work(&selfballoon_worker,
301 selfballoon_interval * HZ);
302
303 return count;
304}
305
Kay Sievers07068022011-12-14 15:32:50 -0800306static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600307 show_selfballooning, store_selfballooning);
308
309SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
310
Kay Sievers07068022011-12-14 15:32:50 -0800311static ssize_t store_selfballoon_interval(struct device *dev,
312 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600313 const char *buf,
314 size_t count)
315{
316 unsigned long val;
317 int err;
318
319 if (!capable(CAP_SYS_ADMIN))
320 return -EPERM;
321 err = strict_strtoul(buf, 10, &val);
322 if (err || val == 0)
323 return -EINVAL;
324 selfballoon_interval = val;
325 return count;
326}
327
Kay Sievers07068022011-12-14 15:32:50 -0800328static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600329 show_selfballoon_interval, store_selfballoon_interval);
330
331SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
332
Kay Sievers07068022011-12-14 15:32:50 -0800333static ssize_t store_selfballoon_downhys(struct device *dev,
334 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600335 const char *buf,
336 size_t count)
337{
338 unsigned long val;
339 int err;
340
341 if (!capable(CAP_SYS_ADMIN))
342 return -EPERM;
343 err = strict_strtoul(buf, 10, &val);
344 if (err || val == 0)
345 return -EINVAL;
346 selfballoon_downhysteresis = val;
347 return count;
348}
349
Kay Sievers07068022011-12-14 15:32:50 -0800350static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600351 show_selfballoon_downhys, store_selfballoon_downhys);
352
353
354SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
355
Kay Sievers07068022011-12-14 15:32:50 -0800356static ssize_t store_selfballoon_uphys(struct device *dev,
357 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600358 const char *buf,
359 size_t count)
360{
361 unsigned long val;
362 int err;
363
364 if (!capable(CAP_SYS_ADMIN))
365 return -EPERM;
366 err = strict_strtoul(buf, 10, &val);
367 if (err || val == 0)
368 return -EINVAL;
369 selfballoon_uphysteresis = val;
370 return count;
371}
372
Kay Sievers07068022011-12-14 15:32:50 -0800373static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600374 show_selfballoon_uphys, store_selfballoon_uphys);
375
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600376SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
377 selfballoon_min_usable_mb);
378
Kay Sievers07068022011-12-14 15:32:50 -0800379static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
380 struct device_attribute *attr,
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600381 const char *buf,
382 size_t count)
383{
384 unsigned long val;
385 int err;
386
387 if (!capable(CAP_SYS_ADMIN))
388 return -EPERM;
389 err = strict_strtoul(buf, 10, &val);
390 if (err || val == 0)
391 return -EINVAL;
392 selfballoon_min_usable_mb = val;
393 return count;
394}
395
Kay Sievers07068022011-12-14 15:32:50 -0800396static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
Dan Magenheimer38a1ed42011-09-27 08:47:58 -0600397 show_selfballoon_min_usable_mb,
398 store_selfballoon_min_usable_mb);
399
400
Dan Magenheimera50777c2011-07-08 12:26:21 -0600401#ifdef CONFIG_FRONTSWAP
402SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
403
Kay Sievers07068022011-12-14 15:32:50 -0800404static ssize_t store_frontswap_selfshrinking(struct device *dev,
405 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600406 const char *buf,
407 size_t count)
408{
409 bool was_enabled = frontswap_selfshrinking;
410 unsigned long tmp;
411 int err;
412
413 if (!capable(CAP_SYS_ADMIN))
414 return -EPERM;
415 err = strict_strtoul(buf, 10, &tmp);
416 if (err || ((tmp != 0) && (tmp != 1)))
417 return -EINVAL;
418 frontswap_selfshrinking = !!tmp;
419 if (!was_enabled && !xen_selfballooning_enabled &&
420 frontswap_selfshrinking)
421 schedule_delayed_work(&selfballoon_worker,
422 selfballoon_interval * HZ);
423
424 return count;
425}
426
Kay Sievers07068022011-12-14 15:32:50 -0800427static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600428 show_frontswap_selfshrinking, store_frontswap_selfshrinking);
429
430SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
431
Kay Sievers07068022011-12-14 15:32:50 -0800432static ssize_t store_frontswap_inertia(struct device *dev,
433 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600434 const char *buf,
435 size_t count)
436{
437 unsigned long val;
438 int err;
439
440 if (!capable(CAP_SYS_ADMIN))
441 return -EPERM;
442 err = strict_strtoul(buf, 10, &val);
443 if (err || val == 0)
444 return -EINVAL;
445 frontswap_inertia = val;
446 frontswap_inertia_counter = val;
447 return count;
448}
449
Kay Sievers07068022011-12-14 15:32:50 -0800450static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600451 show_frontswap_inertia, store_frontswap_inertia);
452
453SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
454
Kay Sievers07068022011-12-14 15:32:50 -0800455static ssize_t store_frontswap_hysteresis(struct device *dev,
456 struct device_attribute *attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600457 const char *buf,
458 size_t count)
459{
460 unsigned long val;
461 int err;
462
463 if (!capable(CAP_SYS_ADMIN))
464 return -EPERM;
465 err = strict_strtoul(buf, 10, &val);
466 if (err || val == 0)
467 return -EINVAL;
468 frontswap_hysteresis = val;
469 return count;
470}
471
Kay Sievers07068022011-12-14 15:32:50 -0800472static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600473 show_frontswap_hysteresis, store_frontswap_hysteresis);
474
475#endif /* CONFIG_FRONTSWAP */
476
477static struct attribute *selfballoon_attrs[] = {
Kay Sievers07068022011-12-14 15:32:50 -0800478 &dev_attr_selfballooning.attr,
479 &dev_attr_selfballoon_interval.attr,
480 &dev_attr_selfballoon_downhysteresis.attr,
481 &dev_attr_selfballoon_uphysteresis.attr,
482 &dev_attr_selfballoon_min_usable_mb.attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600483#ifdef CONFIG_FRONTSWAP
Kay Sievers07068022011-12-14 15:32:50 -0800484 &dev_attr_frontswap_selfshrinking.attr,
485 &dev_attr_frontswap_hysteresis.attr,
486 &dev_attr_frontswap_inertia.attr,
Dan Magenheimera50777c2011-07-08 12:26:21 -0600487#endif
488 NULL
489};
490
Jan Beulichead1d012012-03-14 12:34:19 -0400491static const struct attribute_group selfballoon_group = {
Dan Magenheimera50777c2011-07-08 12:26:21 -0600492 .name = "selfballoon",
493 .attrs = selfballoon_attrs
494};
495#endif
496
Kay Sievers07068022011-12-14 15:32:50 -0800497int register_xen_selfballooning(struct device *dev)
Dan Magenheimera50777c2011-07-08 12:26:21 -0600498{
499 int error = -1;
500
501#ifdef CONFIG_SYSFS
Kay Sievers07068022011-12-14 15:32:50 -0800502 error = sysfs_create_group(&dev->kobj, &selfballoon_group);
Dan Magenheimera50777c2011-07-08 12:26:21 -0600503#endif
504 return error;
505}
506EXPORT_SYMBOL(register_xen_selfballooning);
507
508static int __init xen_selfballoon_init(void)
509{
510 bool enable = false;
511
512 if (!xen_domain())
513 return -ENODEV;
514
515 if (xen_initial_domain()) {
516 pr_info("xen/balloon: Xen selfballooning driver "
517 "disabled for domain0.\n");
518 return -ENODEV;
519 }
520
521 xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
522 if (xen_selfballooning_enabled) {
523 pr_info("xen/balloon: Initializing Xen "
524 "selfballooning driver.\n");
525 enable = true;
526 }
527#ifdef CONFIG_FRONTSWAP
528 frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
529 if (frontswap_selfshrinking) {
530 pr_info("xen/balloon: Initializing frontswap "
531 "selfshrinking driver.\n");
532 enable = true;
533 }
534#endif
535 if (!enable)
536 return -ENODEV;
537
538 schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
539
540 return 0;
541}
542
543subsys_initcall(xen_selfballoon_init);
544
545MODULE_LICENSE("GPL");