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1// SPDX-License-Identifier: GPL-2.0
2/******************************************************************************
3 * Xen selfballoon driver (and optional frontswap self-shrinking driver)
4 *
5 * Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.
6 *
7 * This code complements the cleancache and frontswap patchsets to optimize
8 * support for Xen Transcendent Memory ("tmem"). The policy it implements
9 * is rudimentary and will likely improve over time, but it does work well
10 * enough today.
11 *
12 * Two functionalities are implemented here which both use "control theory"
13 * (feedback) to optimize memory utilization. In a virtualized environment
14 * such as Xen, RAM is often a scarce resource and we would like to ensure
15 * that each of a possibly large number of virtual machines is using RAM
16 * efficiently, i.e. using as little as possible when under light load
17 * and obtaining as much as possible when memory demands are high.
18 * Since RAM needs vary highly dynamically and sometimes dramatically,
19 * "hysteresis" is used, that is, memory target is determined not just
20 * on current data but also on past data stored in the system.
21 *
22 * "Selfballooning" creates memory pressure by managing the Xen balloon
23 * driver to decrease and increase available kernel memory, driven
24 * largely by the target value of "Committed_AS" (see /proc/meminfo).
25 * Since Committed_AS does not account for clean mapped pages (i.e. pages
26 * in RAM that are identical to pages on disk), selfballooning has the
27 * affect of pushing less frequently used clean pagecache pages out of
28 * kernel RAM and, presumably using cleancache, into Xen tmem where
29 * Xen can more efficiently optimize RAM utilization for such pages.
30 *
31 * When kernel memory demand unexpectedly increases faster than Xen, via
32 * the selfballoon driver, is able to (or chooses to) provide usable RAM,
33 * the kernel may invoke swapping. In most cases, frontswap is able
34 * to absorb this swapping into Xen tmem. However, due to the fact
35 * that the kernel swap subsystem assumes swapping occurs to a disk,
36 * swapped pages may sit on the disk for a very long time; even if
37 * the kernel knows the page will never be used again. This is because
38 * the disk space costs very little and can be overwritten when
39 * necessary. When such stale pages are in frontswap, however, they
40 * are taking up valuable real estate. "Frontswap selfshrinking" works
41 * to resolve this: When frontswap activity is otherwise stable
42 * and the guest kernel is not under memory pressure, the "frontswap
43 * selfshrinking" accounts for this by providing pressure to remove some
44 * pages from frontswap and return them to kernel memory.
45 *
46 * For both "selfballooning" and "frontswap-selfshrinking", a worker
47 * thread is used and sysfs tunables are provided to adjust the frequency
48 * and rate of adjustments to achieve the goal, as well as to disable one
49 * or both functions independently.
50 *
51 * While some argue that this functionality can and should be implemented
52 * in userspace, it has been observed that bad things happen (e.g. OOMs).
53 *
54 * System configuration note: Selfballooning should not be enabled on
55 * systems without a sufficiently large swap device configured; for best
56 * results, it is recommended that total swap be increased by the size
57 * of the guest memory. Note, that selfballooning should be disabled by default
58 * if frontswap is not configured. Similarly selfballooning should be enabled
59 * by default if frontswap is configured and can be disabled with the
60 * "tmem.selfballooning=0" kernel boot option. Finally, when frontswap is
61 * configured, frontswap-selfshrinking can be disabled with the
62 * "tmem.selfshrink=0" kernel boot option.
63 *
64 * Selfballooning is disallowed in domain0 and force-disabled.
65 *
66 */
67
68#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
69
70#include <linux/kernel.h>
71#include <linux/memblock.h>
72#include <linux/swap.h>
73#include <linux/mm.h>
74#include <linux/mman.h>
75#include <linux/workqueue.h>
76#include <linux/device.h>
77#include <xen/balloon.h>
78#include <xen/tmem.h>
79#include <xen/xen.h>
80
81/* Enable/disable with sysfs. */
82static int xen_selfballooning_enabled __read_mostly;
83
84/*
85 * Controls rate at which memory target (this iteration) approaches
86 * ultimate goal when memory need is increasing (up-hysteresis) or
87 * decreasing (down-hysteresis). Higher values of hysteresis cause
88 * slower increases/decreases. The default values for the various
89 * parameters were deemed reasonable by experimentation, may be
90 * workload-dependent, and can all be adjusted via sysfs.
91 */
92static unsigned int selfballoon_downhysteresis __read_mostly = 8;
93static unsigned int selfballoon_uphysteresis __read_mostly = 1;
94
95/* In HZ, controls frequency of worker invocation. */
96static unsigned int selfballoon_interval __read_mostly = 5;
97
98/*
99 * Minimum usable RAM in MB for selfballooning target for balloon.
100 * If non-zero, it is added to totalreserve_pages and self-ballooning
101 * will not balloon below the sum. If zero, a piecewise linear function
102 * is calculated as a minimum and added to totalreserve_pages. Note that
103 * setting this value indiscriminately may cause OOMs and crashes.
104 */
105static unsigned int selfballoon_min_usable_mb;
106
107/*
108 * Amount of RAM in MB to add to the target number of pages.
109 * Can be used to reserve some more room for caches and the like.
110 */
111static unsigned int selfballoon_reserved_mb;
112
113static void selfballoon_process(struct work_struct *work);
114static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
115
116#ifdef CONFIG_FRONTSWAP
117#include <linux/frontswap.h>
118
119/* Enable/disable with sysfs. */
120static bool frontswap_selfshrinking __read_mostly;
121
122/*
123 * The default values for the following parameters were deemed reasonable
124 * by experimentation, may be workload-dependent, and can all be
125 * adjusted via sysfs.
126 */
127
128/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
129static unsigned int frontswap_hysteresis __read_mostly = 20;
130
131/*
132 * Number of selfballoon worker invocations to wait before observing that
133 * frontswap selfshrinking should commence. Note that selfshrinking does
134 * not use a separate worker thread.
135 */
136static unsigned int frontswap_inertia __read_mostly = 3;
137
138/* Countdown to next invocation of frontswap_shrink() */
139static unsigned long frontswap_inertia_counter;
140
141/*
142 * Invoked by the selfballoon worker thread, uses current number of pages
143 * in frontswap (frontswap_curr_pages()), previous status, and control
144 * values (hysteresis and inertia) to determine if frontswap should be
145 * shrunk and what the new frontswap size should be. Note that
146 * frontswap_shrink is essentially a partial swapoff that immediately
147 * transfers pages from the "swap device" (frontswap) back into kernel
148 * RAM; despite the name, frontswap "shrinking" is very different from
149 * the "shrinker" interface used by the kernel MM subsystem to reclaim
150 * memory.
151 */
152static void frontswap_selfshrink(void)
153{
154 static unsigned long cur_frontswap_pages;
155 unsigned long last_frontswap_pages;
156 unsigned long tgt_frontswap_pages;
157
158 last_frontswap_pages = cur_frontswap_pages;
159 cur_frontswap_pages = frontswap_curr_pages();
160 if (!cur_frontswap_pages ||
161 (cur_frontswap_pages > last_frontswap_pages)) {
162 frontswap_inertia_counter = frontswap_inertia;
163 return;
164 }
165 if (frontswap_inertia_counter && --frontswap_inertia_counter)
166 return;
167 if (cur_frontswap_pages <= frontswap_hysteresis)
168 tgt_frontswap_pages = 0;
169 else
170 tgt_frontswap_pages = cur_frontswap_pages -
171 (cur_frontswap_pages / frontswap_hysteresis);
172 frontswap_shrink(tgt_frontswap_pages);
173 frontswap_inertia_counter = frontswap_inertia;
174}
175
176#endif /* CONFIG_FRONTSWAP */
177
178#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
179#define PAGES2MB(pages) ((pages) >> (20 - PAGE_SHIFT))
180
181/*
182 * Use current balloon size, the goal (vm_committed_as), and hysteresis
183 * parameters to set a new target balloon size
184 */
185static void selfballoon_process(struct work_struct *work)
186{
187 unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
188 unsigned long useful_pages;
189 bool reset_timer = false;
190
191 if (xen_selfballooning_enabled) {
192 cur_pages = totalram_pages();
193 tgt_pages = cur_pages; /* default is no change */
194 goal_pages = vm_memory_committed() +
195 totalreserve_pages +
196 MB2PAGES(selfballoon_reserved_mb);
197#ifdef CONFIG_FRONTSWAP
198 /* allow space for frontswap pages to be repatriated */
199 if (frontswap_selfshrinking)
200 goal_pages += frontswap_curr_pages();
201#endif
202 if (cur_pages > goal_pages)
203 tgt_pages = cur_pages -
204 ((cur_pages - goal_pages) /
205 selfballoon_downhysteresis);
206 else if (cur_pages < goal_pages)
207 tgt_pages = cur_pages +
208 ((goal_pages - cur_pages) /
209 selfballoon_uphysteresis);
210 /* else if cur_pages == goal_pages, no change */
211 useful_pages = max_pfn - totalreserve_pages;
212 if (selfballoon_min_usable_mb != 0)
213 floor_pages = totalreserve_pages +
214 MB2PAGES(selfballoon_min_usable_mb);
215 /* piecewise linear function ending in ~3% slope */
216 else if (useful_pages < MB2PAGES(16))
217 floor_pages = max_pfn; /* not worth ballooning */
218 else if (useful_pages < MB2PAGES(64))
219 floor_pages = totalreserve_pages + MB2PAGES(16) +
220 ((useful_pages - MB2PAGES(16)) >> 1);
221 else if (useful_pages < MB2PAGES(512))
222 floor_pages = totalreserve_pages + MB2PAGES(40) +
223 ((useful_pages - MB2PAGES(40)) >> 3);
224 else /* useful_pages >= MB2PAGES(512) */
225 floor_pages = totalreserve_pages + MB2PAGES(99) +
226 ((useful_pages - MB2PAGES(99)) >> 5);
227 if (tgt_pages < floor_pages)
228 tgt_pages = floor_pages;
229 balloon_set_new_target(tgt_pages +
230 balloon_stats.current_pages - totalram_pages());
231 reset_timer = true;
232 }
233#ifdef CONFIG_FRONTSWAP
234 if (frontswap_selfshrinking) {
235 frontswap_selfshrink();
236 reset_timer = true;
237 }
238#endif
239 if (reset_timer)
240 schedule_delayed_work(&selfballoon_worker,
241 selfballoon_interval * HZ);
242}
243
244#ifdef CONFIG_SYSFS
245
246#include <linux/capability.h>
247
248#define SELFBALLOON_SHOW(name, format, args...) \
249 static ssize_t show_##name(struct device *dev, \
250 struct device_attribute *attr, \
251 char *buf) \
252 { \
253 return sprintf(buf, format, ##args); \
254 }
255
256SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
257
258static ssize_t store_selfballooning(struct device *dev,
259 struct device_attribute *attr,
260 const char *buf,
261 size_t count)
262{
263 bool was_enabled = xen_selfballooning_enabled;
264 unsigned long tmp;
265 int err;
266
267 if (!capable(CAP_SYS_ADMIN))
268 return -EPERM;
269
270 err = kstrtoul(buf, 10, &tmp);
271 if (err)
272 return err;
273 if ((tmp != 0) && (tmp != 1))
274 return -EINVAL;
275
276 xen_selfballooning_enabled = !!tmp;
277 if (!was_enabled && xen_selfballooning_enabled)
278 schedule_delayed_work(&selfballoon_worker,
279 selfballoon_interval * HZ);
280
281 return count;
282}
283
284static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
285 show_selfballooning, store_selfballooning);
286
287SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
288
289static ssize_t store_selfballoon_interval(struct device *dev,
290 struct device_attribute *attr,
291 const char *buf,
292 size_t count)
293{
294 unsigned long val;
295 int err;
296
297 if (!capable(CAP_SYS_ADMIN))
298 return -EPERM;
299 err = kstrtoul(buf, 10, &val);
300 if (err)
301 return err;
302 if (val == 0)
303 return -EINVAL;
304 selfballoon_interval = val;
305 return count;
306}
307
308static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
309 show_selfballoon_interval, store_selfballoon_interval);
310
311SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
312
313static ssize_t store_selfballoon_downhys(struct device *dev,
314 struct device_attribute *attr,
315 const char *buf,
316 size_t count)
317{
318 unsigned long val;
319 int err;
320
321 if (!capable(CAP_SYS_ADMIN))
322 return -EPERM;
323 err = kstrtoul(buf, 10, &val);
324 if (err)
325 return err;
326 if (val == 0)
327 return -EINVAL;
328 selfballoon_downhysteresis = val;
329 return count;
330}
331
332static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
333 show_selfballoon_downhys, store_selfballoon_downhys);
334
335
336SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
337
338static ssize_t store_selfballoon_uphys(struct device *dev,
339 struct device_attribute *attr,
340 const char *buf,
341 size_t count)
342{
343 unsigned long val;
344 int err;
345
346 if (!capable(CAP_SYS_ADMIN))
347 return -EPERM;
348 err = kstrtoul(buf, 10, &val);
349 if (err)
350 return err;
351 if (val == 0)
352 return -EINVAL;
353 selfballoon_uphysteresis = val;
354 return count;
355}
356
357static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
358 show_selfballoon_uphys, store_selfballoon_uphys);
359
360SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
361 selfballoon_min_usable_mb);
362
363static ssize_t store_selfballoon_min_usable_mb(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 = kstrtoul(buf, 10, &val);
374 if (err)
375 return err;
376 if (val == 0)
377 return -EINVAL;
378 selfballoon_min_usable_mb = val;
379 return count;
380}
381
382static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
383 show_selfballoon_min_usable_mb,
384 store_selfballoon_min_usable_mb);
385
386SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
387 selfballoon_reserved_mb);
388
389static ssize_t store_selfballoon_reserved_mb(struct device *dev,
390 struct device_attribute *attr,
391 const char *buf,
392 size_t count)
393{
394 unsigned long val;
395 int err;
396
397 if (!capable(CAP_SYS_ADMIN))
398 return -EPERM;
399 err = kstrtoul(buf, 10, &val);
400 if (err)
401 return err;
402 if (val == 0)
403 return -EINVAL;
404 selfballoon_reserved_mb = val;
405 return count;
406}
407
408static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
409 show_selfballoon_reserved_mb,
410 store_selfballoon_reserved_mb);
411
412
413#ifdef CONFIG_FRONTSWAP
414SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
415
416static ssize_t store_frontswap_selfshrinking(struct device *dev,
417 struct device_attribute *attr,
418 const char *buf,
419 size_t count)
420{
421 bool was_enabled = frontswap_selfshrinking;
422 unsigned long tmp;
423 int err;
424
425 if (!capable(CAP_SYS_ADMIN))
426 return -EPERM;
427 err = kstrtoul(buf, 10, &tmp);
428 if (err)
429 return err;
430 if ((tmp != 0) && (tmp != 1))
431 return -EINVAL;
432 frontswap_selfshrinking = !!tmp;
433 if (!was_enabled && !xen_selfballooning_enabled &&
434 frontswap_selfshrinking)
435 schedule_delayed_work(&selfballoon_worker,
436 selfballoon_interval * HZ);
437
438 return count;
439}
440
441static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
442 show_frontswap_selfshrinking, store_frontswap_selfshrinking);
443
444SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
445
446static ssize_t store_frontswap_inertia(struct device *dev,
447 struct device_attribute *attr,
448 const char *buf,
449 size_t count)
450{
451 unsigned long val;
452 int err;
453
454 if (!capable(CAP_SYS_ADMIN))
455 return -EPERM;
456 err = kstrtoul(buf, 10, &val);
457 if (err)
458 return err;
459 if (val == 0)
460 return -EINVAL;
461 frontswap_inertia = val;
462 frontswap_inertia_counter = val;
463 return count;
464}
465
466static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
467 show_frontswap_inertia, store_frontswap_inertia);
468
469SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
470
471static ssize_t store_frontswap_hysteresis(struct device *dev,
472 struct device_attribute *attr,
473 const char *buf,
474 size_t count)
475{
476 unsigned long val;
477 int err;
478
479 if (!capable(CAP_SYS_ADMIN))
480 return -EPERM;
481 err = kstrtoul(buf, 10, &val);
482 if (err)
483 return err;
484 if (val == 0)
485 return -EINVAL;
486 frontswap_hysteresis = val;
487 return count;
488}
489
490static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
491 show_frontswap_hysteresis, store_frontswap_hysteresis);
492
493#endif /* CONFIG_FRONTSWAP */
494
495static struct attribute *selfballoon_attrs[] = {
496 &dev_attr_selfballooning.attr,
497 &dev_attr_selfballoon_interval.attr,
498 &dev_attr_selfballoon_downhysteresis.attr,
499 &dev_attr_selfballoon_uphysteresis.attr,
500 &dev_attr_selfballoon_min_usable_mb.attr,
501 &dev_attr_selfballoon_reserved_mb.attr,
502#ifdef CONFIG_FRONTSWAP
503 &dev_attr_frontswap_selfshrinking.attr,
504 &dev_attr_frontswap_hysteresis.attr,
505 &dev_attr_frontswap_inertia.attr,
506#endif
507 NULL
508};
509
510static const struct attribute_group selfballoon_group = {
511 .name = "selfballoon",
512 .attrs = selfballoon_attrs
513};
514#endif
515
516int register_xen_selfballooning(struct device *dev)
517{
518 int error = -1;
519
520#ifdef CONFIG_SYSFS
521 error = sysfs_create_group(&dev->kobj, &selfballoon_group);
522#endif
523 return error;
524}
525EXPORT_SYMBOL(register_xen_selfballooning);
526
527int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
528{
529 bool enable = false;
530 unsigned long reserve_pages;
531
532 if (!xen_domain())
533 return -ENODEV;
534
535 if (xen_initial_domain()) {
536 pr_info("Xen selfballooning driver disabled for domain0\n");
537 return -ENODEV;
538 }
539
540 xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
541 if (xen_selfballooning_enabled) {
542 pr_info("Initializing Xen selfballooning driver\n");
543 enable = true;
544 }
545#ifdef CONFIG_FRONTSWAP
546 frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
547 if (frontswap_selfshrinking) {
548 pr_info("Initializing frontswap selfshrinking driver\n");
549 enable = true;
550 }
551#endif
552 if (!enable)
553 return -ENODEV;
554
555 /*
556 * Give selfballoon_reserved_mb a default value(10% of total ram pages)
557 * to make selfballoon not so aggressive.
558 *
559 * There are mainly two reasons:
560 * 1) The original goal_page didn't consider some pages used by kernel
561 * space, like slab pages and memory used by device drivers.
562 *
563 * 2) The balloon driver may not give back memory to guest OS fast
564 * enough when the workload suddenly aquries a lot of physical memory.
565 *
566 * In both cases, the guest OS will suffer from memory pressure and
567 * OOM killer may be triggered.
568 * By reserving extra 10% of total ram pages, we can keep the system
569 * much more reliably and response faster in some cases.
570 */
571 if (!selfballoon_reserved_mb) {
572 reserve_pages = totalram_pages() / 10;
573 selfballoon_reserved_mb = PAGES2MB(reserve_pages);
574 }
575 schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
576
577 return 0;
578}
579EXPORT_SYMBOL(xen_selfballoon_init);
generated by cgit v1.2.2 (git 2.25.0) at 2025-09-10 01:51:48 -0400