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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. Note, that selfballooning should be disabled by default
57 * if frontswap is not configured. Similarly selfballooning should be enabled
58 * by default if frontswap is configured and can be disabled with the
59 * "tmem.selfballooning=0" kernel boot option. Finally, when frontswap is
60 * configured, frontswap-selfshrinking can be disabled with the
61 * "tmem.selfshrink=0" kernel boot option.
62 *
63 * Selfballooning is disallowed in domain0 and force-disabled.
64 *
65 */
66
67#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
68
69#include <linux/kernel.h>
70#include <linux/bootmem.h>
71#include <linux/swap.h>
72#include <linux/mm.h>
73#include <linux/mman.h>
74#include <linux/workqueue.h>
75#include <linux/device.h>
76#include <xen/balloon.h>
77#include <xen/tmem.h>
78#include <xen/xen.h>
79
80/* Enable/disable with sysfs. */
81static int xen_selfballooning_enabled __read_mostly;
82
83/*
84 * Controls rate at which memory target (this iteration) approaches
85 * ultimate goal when memory need is increasing (up-hysteresis) or
86 * decreasing (down-hysteresis). Higher values of hysteresis cause
87 * slower increases/decreases. The default values for the various
88 * parameters were deemed reasonable by experimentation, may be
89 * workload-dependent, and can all be adjusted via sysfs.
90 */
91static unsigned int selfballoon_downhysteresis __read_mostly = 8;
92static unsigned int selfballoon_uphysteresis __read_mostly = 1;
93
94/* In HZ, controls frequency of worker invocation. */
95static unsigned int selfballoon_interval __read_mostly = 5;
96
97/*
98 * Minimum usable RAM in MB for selfballooning target for balloon.
99 * If non-zero, it is added to totalreserve_pages and self-ballooning
100 * will not balloon below the sum. If zero, a piecewise linear function
101 * is calculated as a minimum and added to totalreserve_pages. Note that
102 * setting this value indiscriminately may cause OOMs and crashes.
103 */
104static unsigned int selfballoon_min_usable_mb;
105
106/*
107 * Amount of RAM in MB to add to the target number of pages.
108 * Can be used to reserve some more room for caches and the like.
109 */
110static unsigned int selfballoon_reserved_mb;
111
112static void selfballoon_process(struct work_struct *work);
113static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
114
115#ifdef CONFIG_FRONTSWAP
116#include <linux/frontswap.h>
117
118/* Enable/disable with sysfs. */
119static bool frontswap_selfshrinking __read_mostly;
120
121/*
122 * The default values for the following parameters were deemed reasonable
123 * by experimentation, may be workload-dependent, and can all be
124 * adjusted via sysfs.
125 */
126
127/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
128static unsigned int frontswap_hysteresis __read_mostly = 20;
129
130/*
131 * Number of selfballoon worker invocations to wait before observing that
132 * frontswap selfshrinking should commence. Note that selfshrinking does
133 * not use a separate worker thread.
134 */
135static unsigned int frontswap_inertia __read_mostly = 3;
136
137/* Countdown to next invocation of frontswap_shrink() */
138static unsigned long frontswap_inertia_counter;
139
140/*
141 * Invoked by the selfballoon worker thread, uses current number of pages
142 * in frontswap (frontswap_curr_pages()), previous status, and control
143 * values (hysteresis and inertia) to determine if frontswap should be
144 * shrunk and what the new frontswap size should be. Note that
145 * frontswap_shrink is essentially a partial swapoff that immediately
146 * transfers pages from the "swap device" (frontswap) back into kernel
147 * RAM; despite the name, frontswap "shrinking" is very different from
148 * the "shrinker" interface used by the kernel MM subsystem to reclaim
149 * memory.
150 */
151static void frontswap_selfshrink(void)
152{
153 static unsigned long cur_frontswap_pages;
154 static unsigned long last_frontswap_pages;
155 static unsigned long tgt_frontswap_pages;
156
157 last_frontswap_pages = cur_frontswap_pages;
158 cur_frontswap_pages = frontswap_curr_pages();
159 if (!cur_frontswap_pages ||
160 (cur_frontswap_pages > last_frontswap_pages)) {
161 frontswap_inertia_counter = frontswap_inertia;
162 return;
163 }
164 if (frontswap_inertia_counter && --frontswap_inertia_counter)
165 return;
166 if (cur_frontswap_pages <= frontswap_hysteresis)
167 tgt_frontswap_pages = 0;
168 else
169 tgt_frontswap_pages = cur_frontswap_pages -
170 (cur_frontswap_pages / frontswap_hysteresis);
171 frontswap_shrink(tgt_frontswap_pages);
172 frontswap_inertia_counter = frontswap_inertia;
173}
174
175#endif /* CONFIG_FRONTSWAP */
176
177#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
178#define PAGES2MB(pages) ((pages) >> (20 - PAGE_SHIFT))
179
180/*
181 * Use current balloon size, the goal (vm_committed_as), and hysteresis
182 * parameters to set a new target balloon size
183 */
184static void selfballoon_process(struct work_struct *work)
185{
186 unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
187 unsigned long useful_pages;
188 bool reset_timer = false;
189
190 if (xen_selfballooning_enabled) {
191 cur_pages = totalram_pages;
192 tgt_pages = cur_pages; /* default is no change */
193 goal_pages = vm_memory_committed() +
194 totalreserve_pages +
195 MB2PAGES(selfballoon_reserved_mb);
196#ifdef CONFIG_FRONTSWAP
197 /* allow space for frontswap pages to be repatriated */
198 if (frontswap_selfshrinking)
199 goal_pages += frontswap_curr_pages();
200#endif
201 if (cur_pages > goal_pages)
202 tgt_pages = cur_pages -
203 ((cur_pages - goal_pages) /
204 selfballoon_downhysteresis);
205 else if (cur_pages < goal_pages)
206 tgt_pages = cur_pages +
207 ((goal_pages - cur_pages) /
208 selfballoon_uphysteresis);
209 /* else if cur_pages == goal_pages, no change */
210 useful_pages = max_pfn - totalreserve_pages;
211 if (selfballoon_min_usable_mb != 0)
212 floor_pages = totalreserve_pages +
213 MB2PAGES(selfballoon_min_usable_mb);
214 /* piecewise linear function ending in ~3% slope */
215 else if (useful_pages < MB2PAGES(16))
216 floor_pages = max_pfn; /* not worth ballooning */
217 else if (useful_pages < MB2PAGES(64))
218 floor_pages = totalreserve_pages + MB2PAGES(16) +
219 ((useful_pages - MB2PAGES(16)) >> 1);
220 else if (useful_pages < MB2PAGES(512))
221 floor_pages = totalreserve_pages + MB2PAGES(40) +
222 ((useful_pages - MB2PAGES(40)) >> 3);
223 else /* useful_pages >= MB2PAGES(512) */
224 floor_pages = totalreserve_pages + MB2PAGES(99) +
225 ((useful_pages - MB2PAGES(99)) >> 5);
226 if (tgt_pages < floor_pages)
227 tgt_pages = floor_pages;
228 balloon_set_new_target(tgt_pages +
229 balloon_stats.current_pages - totalram_pages);
230 reset_timer = true;
231 }
232#ifdef CONFIG_FRONTSWAP
233 if (frontswap_selfshrinking) {
234 frontswap_selfshrink();
235 reset_timer = true;
236 }
237#endif
238 if (reset_timer)
239 schedule_delayed_work(&selfballoon_worker,
240 selfballoon_interval * HZ);
241}
242
243#ifdef CONFIG_SYSFS
244
245#include <linux/capability.h>
246
247#define SELFBALLOON_SHOW(name, format, args...) \
248 static ssize_t show_##name(struct device *dev, \
249 struct device_attribute *attr, \
250 char *buf) \
251 { \
252 return sprintf(buf, format, ##args); \
253 }
254
255SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
256
257static ssize_t store_selfballooning(struct device *dev,
258 struct device_attribute *attr,
259 const char *buf,
260 size_t count)
261{
262 bool was_enabled = xen_selfballooning_enabled;
263 unsigned long tmp;
264 int err;
265
266 if (!capable(CAP_SYS_ADMIN))
267 return -EPERM;
268
269 err = kstrtoul(buf, 10, &tmp);
270 if (err)
271 return err;
272 if ((tmp != 0) && (tmp != 1))
273 return -EINVAL;
274
275 xen_selfballooning_enabled = !!tmp;
276 if (!was_enabled && xen_selfballooning_enabled)
277 schedule_delayed_work(&selfballoon_worker,
278 selfballoon_interval * HZ);
279
280 return count;
281}
282
283static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
284 show_selfballooning, store_selfballooning);
285
286SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
287
288static ssize_t store_selfballoon_interval(struct device *dev,
289 struct device_attribute *attr,
290 const char *buf,
291 size_t count)
292{
293 unsigned long val;
294 int err;
295
296 if (!capable(CAP_SYS_ADMIN))
297 return -EPERM;
298 err = kstrtoul(buf, 10, &val);
299 if (err)
300 return err;
301 if (val == 0)
302 return -EINVAL;
303 selfballoon_interval = val;
304 return count;
305}
306
307static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
308 show_selfballoon_interval, store_selfballoon_interval);
309
310SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
311
312static ssize_t store_selfballoon_downhys(struct device *dev,
313 struct device_attribute *attr,
314 const char *buf,
315 size_t count)
316{
317 unsigned long val;
318 int err;
319
320 if (!capable(CAP_SYS_ADMIN))
321 return -EPERM;
322 err = kstrtoul(buf, 10, &val);
323 if (err)
324 return err;
325 if (val == 0)
326 return -EINVAL;
327 selfballoon_downhysteresis = val;
328 return count;
329}
330
331static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
332 show_selfballoon_downhys, store_selfballoon_downhys);
333
334
335SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
336
337static ssize_t store_selfballoon_uphys(struct device *dev,
338 struct device_attribute *attr,
339 const char *buf,
340 size_t count)
341{
342 unsigned long val;
343 int err;
344
345 if (!capable(CAP_SYS_ADMIN))
346 return -EPERM;
347 err = kstrtoul(buf, 10, &val);
348 if (err)
349 return err;
350 if (val == 0)
351 return -EINVAL;
352 selfballoon_uphysteresis = val;
353 return count;
354}
355
356static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
357 show_selfballoon_uphys, store_selfballoon_uphys);
358
359SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
360 selfballoon_min_usable_mb);
361
362static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
363 struct device_attribute *attr,
364 const char *buf,
365 size_t count)
366{
367 unsigned long val;
368 int err;
369
370 if (!capable(CAP_SYS_ADMIN))
371 return -EPERM;
372 err = kstrtoul(buf, 10, &val);
373 if (err)
374 return err;
375 if (val == 0)
376 return -EINVAL;
377 selfballoon_min_usable_mb = val;
378 return count;
379}
380
381static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
382 show_selfballoon_min_usable_mb,
383 store_selfballoon_min_usable_mb);
384
385SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
386 selfballoon_reserved_mb);
387
388static ssize_t store_selfballoon_reserved_mb(struct device *dev,
389 struct device_attribute *attr,
390 const char *buf,
391 size_t count)
392{
393 unsigned long val;
394 int err;
395
396 if (!capable(CAP_SYS_ADMIN))
397 return -EPERM;
398 err = kstrtoul(buf, 10, &val);
399 if (err)
400 return err;
401 if (val == 0)
402 return -EINVAL;
403 selfballoon_reserved_mb = val;
404 return count;
405}
406
407static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
408 show_selfballoon_reserved_mb,
409 store_selfballoon_reserved_mb);
410
411
412#ifdef CONFIG_FRONTSWAP
413SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
414
415static ssize_t store_frontswap_selfshrinking(struct device *dev,
416 struct device_attribute *attr,
417 const char *buf,
418 size_t count)
419{
420 bool was_enabled = frontswap_selfshrinking;
421 unsigned long tmp;
422 int err;
423
424 if (!capable(CAP_SYS_ADMIN))
425 return -EPERM;
426 err = kstrtoul(buf, 10, &tmp);
427 if (err)
428 return err;
429 if ((tmp != 0) && (tmp != 1))
430 return -EINVAL;
431 frontswap_selfshrinking = !!tmp;
432 if (!was_enabled && !xen_selfballooning_enabled &&
433 frontswap_selfshrinking)
434 schedule_delayed_work(&selfballoon_worker,
435 selfballoon_interval * HZ);
436
437 return count;
438}
439
440static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
441 show_frontswap_selfshrinking, store_frontswap_selfshrinking);
442
443SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
444
445static ssize_t store_frontswap_inertia(struct device *dev,
446 struct device_attribute *attr,
447 const char *buf,
448 size_t count)
449{
450 unsigned long val;
451 int err;
452
453 if (!capable(CAP_SYS_ADMIN))
454 return -EPERM;
455 err = kstrtoul(buf, 10, &val);
456 if (err)
457 return err;
458 if (val == 0)
459 return -EINVAL;
460 frontswap_inertia = val;
461 frontswap_inertia_counter = val;
462 return count;
463}
464
465static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
466 show_frontswap_inertia, store_frontswap_inertia);
467
468SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
469
470static ssize_t store_frontswap_hysteresis(struct device *dev,
471 struct device_attribute *attr,
472 const char *buf,
473 size_t count)
474{
475 unsigned long val;
476 int err;
477
478 if (!capable(CAP_SYS_ADMIN))
479 return -EPERM;
480 err = kstrtoul(buf, 10, &val);
481 if (err)
482 return err;
483 if (val == 0)
484 return -EINVAL;
485 frontswap_hysteresis = val;
486 return count;
487}
488
489static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
490 show_frontswap_hysteresis, store_frontswap_hysteresis);
491
492#endif /* CONFIG_FRONTSWAP */
493
494static struct attribute *selfballoon_attrs[] = {
495 &dev_attr_selfballooning.attr,
496 &dev_attr_selfballoon_interval.attr,
497 &dev_attr_selfballoon_downhysteresis.attr,
498 &dev_attr_selfballoon_uphysteresis.attr,
499 &dev_attr_selfballoon_min_usable_mb.attr,
500 &dev_attr_selfballoon_reserved_mb.attr,
501#ifdef CONFIG_FRONTSWAP
502 &dev_attr_frontswap_selfshrinking.attr,
503 &dev_attr_frontswap_hysteresis.attr,
504 &dev_attr_frontswap_inertia.attr,
505#endif
506 NULL
507};
508
509static const struct attribute_group selfballoon_group = {
510 .name = "selfballoon",
511 .attrs = selfballoon_attrs
512};
513#endif
514
515int register_xen_selfballooning(struct device *dev)
516{
517 int error = -1;
518
519#ifdef CONFIG_SYSFS
520 error = sysfs_create_group(&dev->kobj, &selfballoon_group);
521#endif
522 return error;
523}
524EXPORT_SYMBOL(register_xen_selfballooning);
525
526int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
527{
528 bool enable = false;
529 unsigned long reserve_pages;
530
531 if (!xen_domain())
532 return -ENODEV;
533
534 if (xen_initial_domain()) {
535 pr_info("Xen selfballooning driver disabled for domain0\n");
536 return -ENODEV;
537 }
538
539 xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
540 if (xen_selfballooning_enabled) {
541 pr_info("Initializing Xen selfballooning driver\n");
542 enable = true;
543 }
544#ifdef CONFIG_FRONTSWAP
545 frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
546 if (frontswap_selfshrinking) {
547 pr_info("Initializing frontswap selfshrinking driver\n");
548 enable = true;
549 }
550#endif
551 if (!enable)
552 return -ENODEV;
553
554 /*
555 * Give selfballoon_reserved_mb a default value(10% of total ram pages)
556 * to make selfballoon not so aggressive.
557 *
558 * There are mainly two reasons:
559 * 1) The original goal_page didn't consider some pages used by kernel
560 * space, like slab pages and memory used by device drivers.
561 *
562 * 2) The balloon driver may not give back memory to guest OS fast
563 * enough when the workload suddenly aquries a lot of physical memory.
564 *
565 * In both cases, the guest OS will suffer from memory pressure and
566 * OOM killer may be triggered.
567 * By reserving extra 10% of total ram pages, we can keep the system
568 * much more reliably and response faster in some cases.
569 */
570 if (!selfballoon_reserved_mb) {
571 reserve_pages = totalram_pages / 10;
572 selfballoon_reserved_mb = PAGES2MB(reserve_pages);
573 }
574 schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
575
576 return 0;
577}
578EXPORT_SYMBOL(xen_selfballoon_init);