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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/bootmem.h>
72#include <linux/swap.h>
73#include <linux/mm.h>
74#include <linux/mman.h>
75#include <linux/module.h>
76#include <linux/workqueue.h>
77#include <linux/device.h>
78#include <xen/balloon.h>
79#include <xen/tmem.h>
80#include <xen/xen.h>
81
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
99/*
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
108/*
109 * Amount of RAM in MB to add to the target number of pages.
110 * Can be used to reserve some more room for caches and the like.
111 */
112static unsigned int selfballoon_reserved_mb;
113
114static void selfballoon_process(struct work_struct *work);
115static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
116
117#ifdef CONFIG_FRONTSWAP
118#include <linux/frontswap.h>
119
120/* Enable/disable with sysfs. */
121static bool frontswap_selfshrinking __read_mostly;
122
123/* Enable/disable with kernel boot option. */
124static bool use_frontswap_selfshrink __initdata = true;
125
126/*
127 * The default values for the following parameters were deemed reasonable
128 * by experimentation, may be workload-dependent, and can all be
129 * adjusted via sysfs.
130 */
131
132/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
133static unsigned int frontswap_hysteresis __read_mostly = 20;
134
135/*
136 * Number of selfballoon worker invocations to wait before observing that
137 * frontswap selfshrinking should commence. Note that selfshrinking does
138 * not use a separate worker thread.
139 */
140static unsigned int frontswap_inertia __read_mostly = 3;
141
142/* Countdown to next invocation of frontswap_shrink() */
143static unsigned long frontswap_inertia_counter;
144
145/*
146 * Invoked by the selfballoon worker thread, uses current number of pages
147 * in frontswap (frontswap_curr_pages()), previous status, and control
148 * values (hysteresis and inertia) to determine if frontswap should be
149 * shrunk and what the new frontswap size should be. Note that
150 * frontswap_shrink is essentially a partial swapoff that immediately
151 * transfers pages from the "swap device" (frontswap) back into kernel
152 * RAM; despite the name, frontswap "shrinking" is very different from
153 * the "shrinker" interface used by the kernel MM subsystem to reclaim
154 * memory.
155 */
156static void frontswap_selfshrink(void)
157{
158 static unsigned long cur_frontswap_pages;
159 static unsigned long last_frontswap_pages;
160 static unsigned long tgt_frontswap_pages;
161
162 last_frontswap_pages = cur_frontswap_pages;
163 cur_frontswap_pages = frontswap_curr_pages();
164 if (!cur_frontswap_pages ||
165 (cur_frontswap_pages > last_frontswap_pages)) {
166 frontswap_inertia_counter = frontswap_inertia;
167 return;
168 }
169 if (frontswap_inertia_counter && --frontswap_inertia_counter)
170 return;
171 if (cur_frontswap_pages <= frontswap_hysteresis)
172 tgt_frontswap_pages = 0;
173 else
174 tgt_frontswap_pages = cur_frontswap_pages -
175 (cur_frontswap_pages / frontswap_hysteresis);
176 frontswap_shrink(tgt_frontswap_pages);
177}
178
179static int __init xen_nofrontswap_selfshrink_setup(char *s)
180{
181 use_frontswap_selfshrink = false;
182 return 1;
183}
184
185__setup("noselfshrink", xen_nofrontswap_selfshrink_setup);
186
187/* Disable with kernel boot option. */
188static bool use_selfballooning __initdata = true;
189
190static int __init xen_noselfballooning_setup(char *s)
191{
192 use_selfballooning = false;
193 return 1;
194}
195
196__setup("noselfballooning", xen_noselfballooning_setup);
197#else /* !CONFIG_FRONTSWAP */
198/* Enable with kernel boot option. */
199static bool use_selfballooning __initdata = false;
200
201static int __init xen_selfballooning_setup(char *s)
202{
203 use_selfballooning = true;
204 return 1;
205}
206
207__setup("selfballooning", xen_selfballooning_setup);
208#endif /* CONFIG_FRONTSWAP */
209
210#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
211
212/*
213 * Use current balloon size, the goal (vm_committed_as), and hysteresis
214 * parameters to set a new target balloon size
215 */
216static void selfballoon_process(struct work_struct *work)
217{
218 unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
219 unsigned long useful_pages;
220 bool reset_timer = false;
221
222 if (xen_selfballooning_enabled) {
223 cur_pages = totalram_pages;
224 tgt_pages = cur_pages; /* default is no change */
225 goal_pages = percpu_counter_read_positive(&vm_committed_as) +
226 totalreserve_pages +
227 MB2PAGES(selfballoon_reserved_mb);
228#ifdef CONFIG_FRONTSWAP
229 /* allow space for frontswap pages to be repatriated */
230 if (frontswap_selfshrinking && frontswap_enabled)
231 goal_pages += frontswap_curr_pages();
232#endif
233 if (cur_pages > goal_pages)
234 tgt_pages = cur_pages -
235 ((cur_pages - goal_pages) /
236 selfballoon_downhysteresis);
237 else if (cur_pages < goal_pages)
238 tgt_pages = cur_pages +
239 ((goal_pages - cur_pages) /
240 selfballoon_uphysteresis);
241 /* else if cur_pages == goal_pages, no change */
242 useful_pages = max_pfn - totalreserve_pages;
243 if (selfballoon_min_usable_mb != 0)
244 floor_pages = totalreserve_pages +
245 MB2PAGES(selfballoon_min_usable_mb);
246 /* piecewise linear function ending in ~3% slope */
247 else if (useful_pages < MB2PAGES(16))
248 floor_pages = max_pfn; /* not worth ballooning */
249 else if (useful_pages < MB2PAGES(64))
250 floor_pages = totalreserve_pages + MB2PAGES(16) +
251 ((useful_pages - MB2PAGES(16)) >> 1);
252 else if (useful_pages < MB2PAGES(512))
253 floor_pages = totalreserve_pages + MB2PAGES(40) +
254 ((useful_pages - MB2PAGES(40)) >> 3);
255 else /* useful_pages >= MB2PAGES(512) */
256 floor_pages = totalreserve_pages + MB2PAGES(99) +
257 ((useful_pages - MB2PAGES(99)) >> 5);
258 if (tgt_pages < floor_pages)
259 tgt_pages = floor_pages;
260 balloon_set_new_target(tgt_pages +
261 balloon_stats.current_pages - totalram_pages);
262 reset_timer = true;
263 }
264#ifdef CONFIG_FRONTSWAP
265 if (frontswap_selfshrinking && frontswap_enabled) {
266 frontswap_selfshrink();
267 reset_timer = true;
268 }
269#endif
270 if (reset_timer)
271 schedule_delayed_work(&selfballoon_worker,
272 selfballoon_interval * HZ);
273}
274
275#ifdef CONFIG_SYSFS
276
277#include <linux/capability.h>
278
279#define SELFBALLOON_SHOW(name, format, args...) \
280 static ssize_t show_##name(struct device *dev, \
281 struct device_attribute *attr, \
282 char *buf) \
283 { \
284 return sprintf(buf, format, ##args); \
285 }
286
287SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
288
289static ssize_t store_selfballooning(struct device *dev,
290 struct device_attribute *attr,
291 const char *buf,
292 size_t count)
293{
294 bool was_enabled = xen_selfballooning_enabled;
295 unsigned long tmp;
296 int err;
297
298 if (!capable(CAP_SYS_ADMIN))
299 return -EPERM;
300
301 err = strict_strtoul(buf, 10, &tmp);
302 if (err || ((tmp != 0) && (tmp != 1)))
303 return -EINVAL;
304
305 xen_selfballooning_enabled = !!tmp;
306 if (!was_enabled && xen_selfballooning_enabled)
307 schedule_delayed_work(&selfballoon_worker,
308 selfballoon_interval * HZ);
309
310 return count;
311}
312
313static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
314 show_selfballooning, store_selfballooning);
315
316SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
317
318static ssize_t store_selfballoon_interval(struct device *dev,
319 struct device_attribute *attr,
320 const char *buf,
321 size_t count)
322{
323 unsigned long val;
324 int err;
325
326 if (!capable(CAP_SYS_ADMIN))
327 return -EPERM;
328 err = strict_strtoul(buf, 10, &val);
329 if (err || val == 0)
330 return -EINVAL;
331 selfballoon_interval = val;
332 return count;
333}
334
335static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
336 show_selfballoon_interval, store_selfballoon_interval);
337
338SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
339
340static ssize_t store_selfballoon_downhys(struct device *dev,
341 struct device_attribute *attr,
342 const char *buf,
343 size_t count)
344{
345 unsigned long val;
346 int err;
347
348 if (!capable(CAP_SYS_ADMIN))
349 return -EPERM;
350 err = strict_strtoul(buf, 10, &val);
351 if (err || val == 0)
352 return -EINVAL;
353 selfballoon_downhysteresis = val;
354 return count;
355}
356
357static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
358 show_selfballoon_downhys, store_selfballoon_downhys);
359
360
361SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
362
363static ssize_t store_selfballoon_uphys(struct device *dev,
364 struct device_attribute *attr,
365 const char *buf,
366 size_t count)
367{
368 unsigned long val;
369 int err;
370
371 if (!capable(CAP_SYS_ADMIN))
372 return -EPERM;
373 err = strict_strtoul(buf, 10, &val);
374 if (err || val == 0)
375 return -EINVAL;
376 selfballoon_uphysteresis = val;
377 return count;
378}
379
380static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
381 show_selfballoon_uphys, store_selfballoon_uphys);
382
383SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
384 selfballoon_min_usable_mb);
385
386static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
387 struct device_attribute *attr,
388 const char *buf,
389 size_t count)
390{
391 unsigned long val;
392 int err;
393
394 if (!capable(CAP_SYS_ADMIN))
395 return -EPERM;
396 err = strict_strtoul(buf, 10, &val);
397 if (err || val == 0)
398 return -EINVAL;
399 selfballoon_min_usable_mb = val;
400 return count;
401}
402
403static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
404 show_selfballoon_min_usable_mb,
405 store_selfballoon_min_usable_mb);
406
407SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
408 selfballoon_reserved_mb);
409
410static ssize_t store_selfballoon_reserved_mb(struct device *dev,
411 struct device_attribute *attr,
412 const char *buf,
413 size_t count)
414{
415 unsigned long val;
416 int err;
417
418 if (!capable(CAP_SYS_ADMIN))
419 return -EPERM;
420 err = strict_strtoul(buf, 10, &val);
421 if (err || val == 0)
422 return -EINVAL;
423 selfballoon_reserved_mb = val;
424 return count;
425}
426
427static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
428 show_selfballoon_reserved_mb,
429 store_selfballoon_reserved_mb);
430
431
432#ifdef CONFIG_FRONTSWAP
433SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
434
435static ssize_t store_frontswap_selfshrinking(struct device *dev,
436 struct device_attribute *attr,
437 const char *buf,
438 size_t count)
439{
440 bool was_enabled = frontswap_selfshrinking;
441 unsigned long tmp;
442 int err;
443
444 if (!capable(CAP_SYS_ADMIN))
445 return -EPERM;
446 err = strict_strtoul(buf, 10, &tmp);
447 if (err || ((tmp != 0) && (tmp != 1)))
448 return -EINVAL;
449 frontswap_selfshrinking = !!tmp;
450 if (!was_enabled && !xen_selfballooning_enabled &&
451 frontswap_selfshrinking)
452 schedule_delayed_work(&selfballoon_worker,
453 selfballoon_interval * HZ);
454
455 return count;
456}
457
458static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
459 show_frontswap_selfshrinking, store_frontswap_selfshrinking);
460
461SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
462
463static ssize_t store_frontswap_inertia(struct device *dev,
464 struct device_attribute *attr,
465 const char *buf,
466 size_t count)
467{
468 unsigned long val;
469 int err;
470
471 if (!capable(CAP_SYS_ADMIN))
472 return -EPERM;
473 err = strict_strtoul(buf, 10, &val);
474 if (err || val == 0)
475 return -EINVAL;
476 frontswap_inertia = val;
477 frontswap_inertia_counter = val;
478 return count;
479}
480
481static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
482 show_frontswap_inertia, store_frontswap_inertia);
483
484SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
485
486static ssize_t store_frontswap_hysteresis(struct device *dev,
487 struct device_attribute *attr,
488 const char *buf,
489 size_t count)
490{
491 unsigned long val;
492 int err;
493
494 if (!capable(CAP_SYS_ADMIN))
495 return -EPERM;
496 err = strict_strtoul(buf, 10, &val);
497 if (err || val == 0)
498 return -EINVAL;
499 frontswap_hysteresis = val;
500 return count;
501}
502
503static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
504 show_frontswap_hysteresis, store_frontswap_hysteresis);
505
506#endif /* CONFIG_FRONTSWAP */
507
508static struct attribute *selfballoon_attrs[] = {
509 &dev_attr_selfballooning.attr,
510 &dev_attr_selfballoon_interval.attr,
511 &dev_attr_selfballoon_downhysteresis.attr,
512 &dev_attr_selfballoon_uphysteresis.attr,
513 &dev_attr_selfballoon_min_usable_mb.attr,
514 &dev_attr_selfballoon_reserved_mb.attr,
515#ifdef CONFIG_FRONTSWAP
516 &dev_attr_frontswap_selfshrinking.attr,
517 &dev_attr_frontswap_hysteresis.attr,
518 &dev_attr_frontswap_inertia.attr,
519#endif
520 NULL
521};
522
523static const struct attribute_group selfballoon_group = {
524 .name = "selfballoon",
525 .attrs = selfballoon_attrs
526};
527#endif
528
529int register_xen_selfballooning(struct device *dev)
530{
531 int error = -1;
532
533#ifdef CONFIG_SYSFS
534 error = sysfs_create_group(&dev->kobj, &selfballoon_group);
535#endif
536 return error;
537}
538EXPORT_SYMBOL(register_xen_selfballooning);
539
540static int __init xen_selfballoon_init(void)
541{
542 bool enable = false;
543
544 if (!xen_domain())
545 return -ENODEV;
546
547 if (xen_initial_domain()) {
548 pr_info("xen/balloon: Xen selfballooning driver "
549 "disabled for domain0.\n");
550 return -ENODEV;
551 }
552
553 xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
554 if (xen_selfballooning_enabled) {
555 pr_info("xen/balloon: Initializing Xen "
556 "selfballooning driver.\n");
557 enable = true;
558 }
559#ifdef CONFIG_FRONTSWAP
560 frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
561 if (frontswap_selfshrinking) {
562 pr_info("xen/balloon: Initializing frontswap "
563 "selfshrinking driver.\n");
564 enable = true;
565 }
566#endif
567 if (!enable)
568 return -ENODEV;
569
570 schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
571
572 return 0;
573}
574
575subsys_initcall(xen_selfballoon_init);
576
577MODULE_LICENSE("GPL");