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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
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>
71#include <linux/mm.h>
72#include <linux/mman.h>
73#include <linux/module.h>
74#include <linux/workqueue.h>
75#include <xen/balloon.h>
76#include <xen/tmem.h>
77#include <xen/xen.h>
78
79/* Enable/disable with sysfs. */
80static int xen_selfballooning_enabled __read_mostly;
81
82/*
83 * Controls rate at which memory target (this iteration) approaches
84 * ultimate goal when memory need is increasing (up-hysteresis) or
85 * decreasing (down-hysteresis). Higher values of hysteresis cause
86 * slower increases/decreases. The default values for the various
87 * parameters were deemed reasonable by experimentation, may be
88 * workload-dependent, and can all be adjusted via sysfs.
89 */
90static unsigned int selfballoon_downhysteresis __read_mostly = 8;
91static unsigned int selfballoon_uphysteresis __read_mostly = 1;
92
93/* In HZ, controls frequency of worker invocation. */
94static unsigned int selfballoon_interval __read_mostly = 5;
95
96static void selfballoon_process(struct work_struct *work);
97static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
98
99#ifdef CONFIG_FRONTSWAP
100#include <linux/frontswap.h>
101
102/* Enable/disable with sysfs. */
103static bool frontswap_selfshrinking __read_mostly;
104
105/* Enable/disable with kernel boot option. */
106static bool use_frontswap_selfshrink __initdata = true;
107
108/*
109 * The default values for the following parameters were deemed reasonable
110 * by experimentation, may be workload-dependent, and can all be
111 * adjusted via sysfs.
112 */
113
114/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
115static unsigned int frontswap_hysteresis __read_mostly = 20;
116
117/*
118 * Number of selfballoon worker invocations to wait before observing that
119 * frontswap selfshrinking should commence. Note that selfshrinking does
120 * not use a separate worker thread.
121 */
122static unsigned int frontswap_inertia __read_mostly = 3;
123
124/* Countdown to next invocation of frontswap_shrink() */
125static unsigned long frontswap_inertia_counter;
126
127/*
128 * Invoked by the selfballoon worker thread, uses current number of pages
129 * in frontswap (frontswap_curr_pages()), previous status, and control
130 * values (hysteresis and inertia) to determine if frontswap should be
131 * shrunk and what the new frontswap size should be. Note that
132 * frontswap_shrink is essentially a partial swapoff that immediately
133 * transfers pages from the "swap device" (frontswap) back into kernel
134 * RAM; despite the name, frontswap "shrinking" is very different from
135 * the "shrinker" interface used by the kernel MM subsystem to reclaim
136 * memory.
137 */
138static void frontswap_selfshrink(void)
139{
140 static unsigned long cur_frontswap_pages;
141 static unsigned long last_frontswap_pages;
142 static unsigned long tgt_frontswap_pages;
143
144 last_frontswap_pages = cur_frontswap_pages;
145 cur_frontswap_pages = frontswap_curr_pages();
146 if (!cur_frontswap_pages ||
147 (cur_frontswap_pages > last_frontswap_pages)) {
148 frontswap_inertia_counter = frontswap_inertia;
149 return;
150 }
151 if (frontswap_inertia_counter && --frontswap_inertia_counter)
152 return;
153 if (cur_frontswap_pages <= frontswap_hysteresis)
154 tgt_frontswap_pages = 0;
155 else
156 tgt_frontswap_pages = cur_frontswap_pages -
157 (cur_frontswap_pages / frontswap_hysteresis);
158 frontswap_shrink(tgt_frontswap_pages);
159}
160
161static int __init xen_nofrontswap_selfshrink_setup(char *s)
162{
163 use_frontswap_selfshrink = false;
164 return 1;
165}
166
167__setup("noselfshrink", xen_nofrontswap_selfshrink_setup);
168
169/* Disable with kernel boot option. */
170static bool use_selfballooning __initdata = true;
171
172static int __init xen_noselfballooning_setup(char *s)
173{
174 use_selfballooning = false;
175 return 1;
176}
177
178__setup("noselfballooning", xen_noselfballooning_setup);
179#else /* !CONFIG_FRONTSWAP */
180/* Enable with kernel boot option. */
181static bool use_selfballooning __initdata = false;
182
183static int __init xen_selfballooning_setup(char *s)
184{
185 use_selfballooning = true;
186 return 1;
187}
188
189__setup("selfballooning", xen_selfballooning_setup);
190#endif /* CONFIG_FRONTSWAP */
191
192/*
193 * Use current balloon size, the goal (vm_committed_as), and hysteresis
194 * parameters to set a new target balloon size
195 */
196static void selfballoon_process(struct work_struct *work)
197{
198 unsigned long cur_pages, goal_pages, tgt_pages;
199 bool reset_timer = false;
200
201 if (xen_selfballooning_enabled) {
202 cur_pages = balloon_stats.current_pages;
203 tgt_pages = cur_pages; /* default is no change */
204 goal_pages = percpu_counter_read_positive(&vm_committed_as) +
205 balloon_stats.current_pages - totalram_pages;
206#ifdef CONFIG_FRONTSWAP
207 /* allow space for frontswap pages to be repatriated */
208 if (frontswap_selfshrinking && frontswap_enabled)
209 goal_pages += frontswap_curr_pages();
210#endif
211 if (cur_pages > goal_pages)
212 tgt_pages = cur_pages -
213 ((cur_pages - goal_pages) /
214 selfballoon_downhysteresis);
215 else if (cur_pages < goal_pages)
216 tgt_pages = cur_pages +
217 ((goal_pages - cur_pages) /
218 selfballoon_uphysteresis);
219 /* else if cur_pages == goal_pages, no change */
220 balloon_set_new_target(tgt_pages);
221 reset_timer = true;
222 }
223#ifdef CONFIG_FRONTSWAP
224 if (frontswap_selfshrinking && frontswap_enabled) {
225 frontswap_selfshrink();
226 reset_timer = true;
227 }
228#endif
229 if (reset_timer)
230 schedule_delayed_work(&selfballoon_worker,
231 selfballoon_interval * HZ);
232}
233
234#ifdef CONFIG_SYSFS
235
236#include <linux/sysdev.h>
237#include <linux/capability.h>
238
239#define SELFBALLOON_SHOW(name, format, args...) \
240 static ssize_t show_##name(struct sys_device *dev, \
241 struct sysdev_attribute *attr, \
242 char *buf) \
243 { \
244 return sprintf(buf, format, ##args); \
245 }
246
247SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
248
249static ssize_t store_selfballooning(struct sys_device *dev,
250 struct sysdev_attribute *attr,
251 const char *buf,
252 size_t count)
253{
254 bool was_enabled = xen_selfballooning_enabled;
255 unsigned long tmp;
256 int err;
257
258 if (!capable(CAP_SYS_ADMIN))
259 return -EPERM;
260
261 err = strict_strtoul(buf, 10, &tmp);
262 if (err || ((tmp != 0) && (tmp != 1)))
263 return -EINVAL;
264
265 xen_selfballooning_enabled = !!tmp;
266 if (!was_enabled && xen_selfballooning_enabled)
267 schedule_delayed_work(&selfballoon_worker,
268 selfballoon_interval * HZ);
269
270 return count;
271}
272
273static SYSDEV_ATTR(selfballooning, S_IRUGO | S_IWUSR,
274 show_selfballooning, store_selfballooning);
275
276SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
277
278static ssize_t store_selfballoon_interval(struct sys_device *dev,
279 struct sysdev_attribute *attr,
280 const char *buf,
281 size_t count)
282{
283 unsigned long val;
284 int err;
285
286 if (!capable(CAP_SYS_ADMIN))
287 return -EPERM;
288 err = strict_strtoul(buf, 10, &val);
289 if (err || val == 0)
290 return -EINVAL;
291 selfballoon_interval = val;
292 return count;
293}
294
295static SYSDEV_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
296 show_selfballoon_interval, store_selfballoon_interval);
297
298SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
299
300static ssize_t store_selfballoon_downhys(struct sys_device *dev,
301 struct sysdev_attribute *attr,
302 const char *buf,
303 size_t count)
304{
305 unsigned long val;
306 int err;
307
308 if (!capable(CAP_SYS_ADMIN))
309 return -EPERM;
310 err = strict_strtoul(buf, 10, &val);
311 if (err || val == 0)
312 return -EINVAL;
313 selfballoon_downhysteresis = val;
314 return count;
315}
316
317static SYSDEV_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
318 show_selfballoon_downhys, store_selfballoon_downhys);
319
320
321SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
322
323static ssize_t store_selfballoon_uphys(struct sys_device *dev,
324 struct sysdev_attribute *attr,
325 const char *buf,
326 size_t count)
327{
328 unsigned long val;
329 int err;
330
331 if (!capable(CAP_SYS_ADMIN))
332 return -EPERM;
333 err = strict_strtoul(buf, 10, &val);
334 if (err || val == 0)
335 return -EINVAL;
336 selfballoon_uphysteresis = val;
337 return count;
338}
339
340static SYSDEV_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
341 show_selfballoon_uphys, store_selfballoon_uphys);
342
343#ifdef CONFIG_FRONTSWAP
344SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
345
346static ssize_t store_frontswap_selfshrinking(struct sys_device *dev,
347 struct sysdev_attribute *attr,
348 const char *buf,
349 size_t count)
350{
351 bool was_enabled = frontswap_selfshrinking;
352 unsigned long tmp;
353 int err;
354
355 if (!capable(CAP_SYS_ADMIN))
356 return -EPERM;
357 err = strict_strtoul(buf, 10, &tmp);
358 if (err || ((tmp != 0) && (tmp != 1)))
359 return -EINVAL;
360 frontswap_selfshrinking = !!tmp;
361 if (!was_enabled && !xen_selfballooning_enabled &&
362 frontswap_selfshrinking)
363 schedule_delayed_work(&selfballoon_worker,
364 selfballoon_interval * HZ);
365
366 return count;
367}
368
369static SYSDEV_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
370 show_frontswap_selfshrinking, store_frontswap_selfshrinking);
371
372SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
373
374static ssize_t store_frontswap_inertia(struct sys_device *dev,
375 struct sysdev_attribute *attr,
376 const char *buf,
377 size_t count)
378{
379 unsigned long val;
380 int err;
381
382 if (!capable(CAP_SYS_ADMIN))
383 return -EPERM;
384 err = strict_strtoul(buf, 10, &val);
385 if (err || val == 0)
386 return -EINVAL;
387 frontswap_inertia = val;
388 frontswap_inertia_counter = val;
389 return count;
390}
391
392static SYSDEV_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
393 show_frontswap_inertia, store_frontswap_inertia);
394
395SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
396
397static ssize_t store_frontswap_hysteresis(struct sys_device *dev,
398 struct sysdev_attribute *attr,
399 const char *buf,
400 size_t count)
401{
402 unsigned long val;
403 int err;
404
405 if (!capable(CAP_SYS_ADMIN))
406 return -EPERM;
407 err = strict_strtoul(buf, 10, &val);
408 if (err || val == 0)
409 return -EINVAL;
410 frontswap_hysteresis = val;
411 return count;
412}
413
414static SYSDEV_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
415 show_frontswap_hysteresis, store_frontswap_hysteresis);
416
417#endif /* CONFIG_FRONTSWAP */
418
419static struct attribute *selfballoon_attrs[] = {
420 &attr_selfballooning.attr,
421 &attr_selfballoon_interval.attr,
422 &attr_selfballoon_downhysteresis.attr,
423 &attr_selfballoon_uphysteresis.attr,
424#ifdef CONFIG_FRONTSWAP
425 &attr_frontswap_selfshrinking.attr,
426 &attr_frontswap_hysteresis.attr,
427 &attr_frontswap_inertia.attr,
428#endif
429 NULL
430};
431
432static struct attribute_group selfballoon_group = {
433 .name = "selfballoon",
434 .attrs = selfballoon_attrs
435};
436#endif
437
438int register_xen_selfballooning(struct sys_device *sysdev)
439{
440 int error = -1;
441
442#ifdef CONFIG_SYSFS
443 error = sysfs_create_group(&sysdev->kobj, &selfballoon_group);
444#endif
445 return error;
446}
447EXPORT_SYMBOL(register_xen_selfballooning);
448
449static int __init xen_selfballoon_init(void)
450{
451 bool enable = false;
452
453 if (!xen_domain())
454 return -ENODEV;
455
456 if (xen_initial_domain()) {
457 pr_info("xen/balloon: Xen selfballooning driver "
458 "disabled for domain0.\n");
459 return -ENODEV;
460 }
461
462 xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
463 if (xen_selfballooning_enabled) {
464 pr_info("xen/balloon: Initializing Xen "
465 "selfballooning driver.\n");
466 enable = true;
467 }
468#ifdef CONFIG_FRONTSWAP
469 frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
470 if (frontswap_selfshrinking) {
471 pr_info("xen/balloon: Initializing frontswap "
472 "selfshrinking driver.\n");
473 enable = true;
474 }
475#endif
476 if (!enable)
477 return -ENODEV;
478
479 schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
480
481 return 0;
482}
483
484subsys_initcall(xen_selfballoon_init);
485
486MODULE_LICENSE("GPL");