Root/drivers/xen/xen-selfballoon.c

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");
578

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