1 /******************************************************************************
2 * Xen selfballoon driver (and optional frontswap self-shrinking driver)
4 * Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.
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
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.
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.
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.
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.
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).
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.
66 * Selfballooning is disallowed in domain0 and force-disabled.
70 #include <linux/kernel.h>
71 #include <linux/bootmem.h>
72 #include <linux/swap.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>
82 /* Enable/disable with sysfs. */
83 static int xen_selfballooning_enabled __read_mostly;
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.
93 static unsigned int selfballoon_downhysteresis __read_mostly = 8;
94 static unsigned int selfballoon_uphysteresis __read_mostly = 1;
96 /* In HZ, controls frequency of worker invocation. */
97 static unsigned int selfballoon_interval __read_mostly = 5;
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.
106 static unsigned int selfballoon_min_usable_mb;
108 static void selfballoon_process(struct work_struct *work);
109 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
111 #ifdef CONFIG_FRONTSWAP
112 #include <linux/frontswap.h>
114 /* Enable/disable with sysfs. */
115 static bool frontswap_selfshrinking __read_mostly;
117 /* Enable/disable with kernel boot option. */
118 static bool use_frontswap_selfshrink __initdata = true;
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.
126 /* Control rate for frontswap shrinking. Higher hysteresis is slower. */
127 static unsigned int frontswap_hysteresis __read_mostly = 20;
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.
134 static unsigned int frontswap_inertia __read_mostly = 3;
136 /* Countdown to next invocation of frontswap_shrink() */
137 static unsigned long frontswap_inertia_counter;
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
150 static void frontswap_selfshrink(void)
152 static unsigned long cur_frontswap_pages;
153 static unsigned long last_frontswap_pages;
154 static unsigned long tgt_frontswap_pages;
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;
163 if (frontswap_inertia_counter && --frontswap_inertia_counter)
165 if (cur_frontswap_pages <= frontswap_hysteresis)
166 tgt_frontswap_pages = 0;
168 tgt_frontswap_pages = cur_frontswap_pages -
169 (cur_frontswap_pages / frontswap_hysteresis);
170 frontswap_shrink(tgt_frontswap_pages);
173 static int __init xen_nofrontswap_selfshrink_setup(char *s)
175 use_frontswap_selfshrink = false;
179 __setup("noselfshrink", xen_nofrontswap_selfshrink_setup);
181 /* Disable with kernel boot option. */
182 static bool use_selfballooning __initdata = true;
184 static int __init xen_noselfballooning_setup(char *s)
186 use_selfballooning = false;
190 __setup("noselfballooning", xen_noselfballooning_setup);
191 #else /* !CONFIG_FRONTSWAP */
192 /* Enable with kernel boot option. */
193 static bool use_selfballooning __initdata = false;
195 static int __init xen_selfballooning_setup(char *s)
197 use_selfballooning = true;
201 __setup("selfballooning", xen_selfballooning_setup);
202 #endif /* CONFIG_FRONTSWAP */
204 #define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
207 * Use current balloon size, the goal (vm_committed_as), and hysteresis
208 * parameters to set a new target balloon size
210 static void selfballoon_process(struct work_struct *work)
212 unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
213 unsigned long useful_pages;
214 bool reset_timer = false;
216 if (xen_selfballooning_enabled) {
217 cur_pages = totalram_pages;
218 tgt_pages = cur_pages; /* default is no change */
219 goal_pages = percpu_counter_read_positive(&vm_committed_as) +
221 #ifdef CONFIG_FRONTSWAP
222 /* allow space for frontswap pages to be repatriated */
223 if (frontswap_selfshrinking && frontswap_enabled)
224 goal_pages += frontswap_curr_pages();
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 */
235 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);
257 #ifdef CONFIG_FRONTSWAP
258 if (frontswap_selfshrinking && frontswap_enabled) {
259 frontswap_selfshrink();
264 schedule_delayed_work(&selfballoon_worker,
265 selfballoon_interval * HZ);
270 #include <linux/capability.h>
272 #define SELFBALLOON_SHOW(name, format, args...) \
273 static ssize_t show_##name(struct device *dev, \
274 struct device_attribute *attr, \
277 return sprintf(buf, format, ##args); \
280 SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
282 static ssize_t store_selfballooning(struct device *dev,
283 struct device_attribute *attr,
287 bool was_enabled = xen_selfballooning_enabled;
291 if (!capable(CAP_SYS_ADMIN))
294 err = strict_strtoul(buf, 10, &tmp);
295 if (err || ((tmp != 0) && (tmp != 1)))
298 xen_selfballooning_enabled = !!tmp;
299 if (!was_enabled && xen_selfballooning_enabled)
300 schedule_delayed_work(&selfballoon_worker,
301 selfballoon_interval * HZ);
306 static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
307 show_selfballooning, store_selfballooning);
309 SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
311 static ssize_t store_selfballoon_interval(struct device *dev,
312 struct device_attribute *attr,
319 if (!capable(CAP_SYS_ADMIN))
321 err = strict_strtoul(buf, 10, &val);
324 selfballoon_interval = val;
328 static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
329 show_selfballoon_interval, store_selfballoon_interval);
331 SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
333 static ssize_t store_selfballoon_downhys(struct device *dev,
334 struct device_attribute *attr,
341 if (!capable(CAP_SYS_ADMIN))
343 err = strict_strtoul(buf, 10, &val);
346 selfballoon_downhysteresis = val;
350 static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
351 show_selfballoon_downhys, store_selfballoon_downhys);
354 SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
356 static ssize_t store_selfballoon_uphys(struct device *dev,
357 struct device_attribute *attr,
364 if (!capable(CAP_SYS_ADMIN))
366 err = strict_strtoul(buf, 10, &val);
369 selfballoon_uphysteresis = val;
373 static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
374 show_selfballoon_uphys, store_selfballoon_uphys);
376 SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
377 selfballoon_min_usable_mb);
379 static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
380 struct device_attribute *attr,
387 if (!capable(CAP_SYS_ADMIN))
389 err = strict_strtoul(buf, 10, &val);
392 selfballoon_min_usable_mb = val;
396 static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
397 show_selfballoon_min_usable_mb,
398 store_selfballoon_min_usable_mb);
401 #ifdef CONFIG_FRONTSWAP
402 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
404 static ssize_t store_frontswap_selfshrinking(struct device *dev,
405 struct device_attribute *attr,
409 bool was_enabled = frontswap_selfshrinking;
413 if (!capable(CAP_SYS_ADMIN))
415 err = strict_strtoul(buf, 10, &tmp);
416 if (err || ((tmp != 0) && (tmp != 1)))
418 frontswap_selfshrinking = !!tmp;
419 if (!was_enabled && !xen_selfballooning_enabled &&
420 frontswap_selfshrinking)
421 schedule_delayed_work(&selfballoon_worker,
422 selfballoon_interval * HZ);
427 static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
428 show_frontswap_selfshrinking, store_frontswap_selfshrinking);
430 SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
432 static ssize_t store_frontswap_inertia(struct device *dev,
433 struct device_attribute *attr,
440 if (!capable(CAP_SYS_ADMIN))
442 err = strict_strtoul(buf, 10, &val);
445 frontswap_inertia = val;
446 frontswap_inertia_counter = val;
450 static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
451 show_frontswap_inertia, store_frontswap_inertia);
453 SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
455 static ssize_t store_frontswap_hysteresis(struct device *dev,
456 struct device_attribute *attr,
463 if (!capable(CAP_SYS_ADMIN))
465 err = strict_strtoul(buf, 10, &val);
468 frontswap_hysteresis = val;
472 static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
473 show_frontswap_hysteresis, store_frontswap_hysteresis);
475 #endif /* CONFIG_FRONTSWAP */
477 static struct attribute *selfballoon_attrs[] = {
478 &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,
483 #ifdef CONFIG_FRONTSWAP
484 &dev_attr_frontswap_selfshrinking.attr,
485 &dev_attr_frontswap_hysteresis.attr,
486 &dev_attr_frontswap_inertia.attr,
491 static const struct attribute_group selfballoon_group = {
492 .name = "selfballoon",
493 .attrs = selfballoon_attrs
497 int register_xen_selfballooning(struct device *dev)
502 error = sysfs_create_group(&dev->kobj, &selfballoon_group);
506 EXPORT_SYMBOL(register_xen_selfballooning);
508 static int __init xen_selfballoon_init(void)
515 if (xen_initial_domain()) {
516 pr_info("xen/balloon: Xen selfballooning driver "
517 "disabled for domain0.\n");
521 xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
522 if (xen_selfballooning_enabled) {
523 pr_info("xen/balloon: Initializing Xen "
524 "selfballooning driver.\n");
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");
538 schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
543 subsys_initcall(xen_selfballoon_init);
545 MODULE_LICENSE("GPL");