Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
[linux-2.6.git] / 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. */
83 static 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  */
93 static unsigned int selfballoon_downhysteresis __read_mostly = 8;
94 static unsigned int selfballoon_uphysteresis __read_mostly = 1;
95
96 /* In HZ, controls frequency of worker invocation. */
97 static 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  */
106 static unsigned int selfballoon_min_usable_mb;
107
108 static void selfballoon_process(struct work_struct *work);
109 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
110
111 #ifdef CONFIG_FRONTSWAP
112 #include <linux/frontswap.h>
113
114 /* Enable/disable with sysfs. */
115 static bool frontswap_selfshrinking __read_mostly;
116
117 /* Enable/disable with kernel boot option. */
118 static bool use_frontswap_selfshrink __initdata = true;
119
120 /*
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.
124  */
125
126 /* Control rate for frontswap shrinking. Higher hysteresis is slower. */
127 static unsigned int frontswap_hysteresis __read_mostly = 20;
128
129 /*
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.
133  */
134 static unsigned int frontswap_inertia __read_mostly = 3;
135
136 /* Countdown to next invocation of frontswap_shrink() */
137 static unsigned long frontswap_inertia_counter;
138
139 /*
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
148  * memory.
149  */
150 static void frontswap_selfshrink(void)
151 {
152         static unsigned long cur_frontswap_pages;
153         static unsigned long last_frontswap_pages;
154         static unsigned long tgt_frontswap_pages;
155
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;
161                 return;
162         }
163         if (frontswap_inertia_counter && --frontswap_inertia_counter)
164                 return;
165         if (cur_frontswap_pages <= frontswap_hysteresis)
166                 tgt_frontswap_pages = 0;
167         else
168                 tgt_frontswap_pages = cur_frontswap_pages -
169                         (cur_frontswap_pages / frontswap_hysteresis);
170         frontswap_shrink(tgt_frontswap_pages);
171 }
172
173 static int __init xen_nofrontswap_selfshrink_setup(char *s)
174 {
175         use_frontswap_selfshrink = false;
176         return 1;
177 }
178
179 __setup("noselfshrink", xen_nofrontswap_selfshrink_setup);
180
181 /* Disable with kernel boot option. */
182 static bool use_selfballooning __initdata = true;
183
184 static int __init xen_noselfballooning_setup(char *s)
185 {
186         use_selfballooning = false;
187         return 1;
188 }
189
190 __setup("noselfballooning", xen_noselfballooning_setup);
191 #else /* !CONFIG_FRONTSWAP */
192 /* Enable with kernel boot option. */
193 static bool use_selfballooning __initdata = false;
194
195 static int __init xen_selfballooning_setup(char *s)
196 {
197         use_selfballooning = true;
198         return 1;
199 }
200
201 __setup("selfballooning", xen_selfballooning_setup);
202 #endif /* CONFIG_FRONTSWAP */
203
204 #define MB2PAGES(mb)    ((mb) << (20 - PAGE_SHIFT))
205
206 /*
207  * Use current balloon size, the goal (vm_committed_as), and hysteresis
208  * parameters to set a new target balloon size
209  */
210 static void selfballoon_process(struct work_struct *work)
211 {
212         unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
213         unsigned long useful_pages;
214         bool reset_timer = false;
215
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) +
220                                 totalreserve_pages;
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();
225 #endif
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);
255                 reset_timer = true;
256         }
257 #ifdef CONFIG_FRONTSWAP
258         if (frontswap_selfshrinking && frontswap_enabled) {
259                 frontswap_selfshrink();
260                 reset_timer = true;
261         }
262 #endif
263         if (reset_timer)
264                 schedule_delayed_work(&selfballoon_worker,
265                         selfballoon_interval * HZ);
266 }
267
268 #ifdef CONFIG_SYSFS
269
270 #include <linux/capability.h>
271
272 #define SELFBALLOON_SHOW(name, format, args...)                         \
273         static ssize_t show_##name(struct device *dev,  \
274                                           struct device_attribute *attr, \
275                                           char *buf) \
276         { \
277                 return sprintf(buf, format, ##args); \
278         }
279
280 SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
281
282 static ssize_t store_selfballooning(struct device *dev,
283                             struct device_attribute *attr,
284                             const char *buf,
285                             size_t count)
286 {
287         bool was_enabled = xen_selfballooning_enabled;
288         unsigned long tmp;
289         int err;
290
291         if (!capable(CAP_SYS_ADMIN))
292                 return -EPERM;
293
294         err = strict_strtoul(buf, 10, &tmp);
295         if (err || ((tmp != 0) && (tmp != 1)))
296                 return -EINVAL;
297
298         xen_selfballooning_enabled = !!tmp;
299         if (!was_enabled && xen_selfballooning_enabled)
300                 schedule_delayed_work(&selfballoon_worker,
301                         selfballoon_interval * HZ);
302
303         return count;
304 }
305
306 static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
307                    show_selfballooning, store_selfballooning);
308
309 SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
310
311 static ssize_t store_selfballoon_interval(struct device *dev,
312                                           struct device_attribute *attr,
313                                           const char *buf,
314                                           size_t count)
315 {
316         unsigned long val;
317         int err;
318
319         if (!capable(CAP_SYS_ADMIN))
320                 return -EPERM;
321         err = strict_strtoul(buf, 10, &val);
322         if (err || val == 0)
323                 return -EINVAL;
324         selfballoon_interval = val;
325         return count;
326 }
327
328 static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
329                    show_selfballoon_interval, store_selfballoon_interval);
330
331 SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
332
333 static ssize_t store_selfballoon_downhys(struct device *dev,
334                                          struct device_attribute *attr,
335                                          const char *buf,
336                                          size_t count)
337 {
338         unsigned long val;
339         int err;
340
341         if (!capable(CAP_SYS_ADMIN))
342                 return -EPERM;
343         err = strict_strtoul(buf, 10, &val);
344         if (err || val == 0)
345                 return -EINVAL;
346         selfballoon_downhysteresis = val;
347         return count;
348 }
349
350 static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
351                    show_selfballoon_downhys, store_selfballoon_downhys);
352
353
354 SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
355
356 static ssize_t store_selfballoon_uphys(struct device *dev,
357                                        struct device_attribute *attr,
358                                        const char *buf,
359                                        size_t count)
360 {
361         unsigned long val;
362         int err;
363
364         if (!capable(CAP_SYS_ADMIN))
365                 return -EPERM;
366         err = strict_strtoul(buf, 10, &val);
367         if (err || val == 0)
368                 return -EINVAL;
369         selfballoon_uphysteresis = val;
370         return count;
371 }
372
373 static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
374                    show_selfballoon_uphys, store_selfballoon_uphys);
375
376 SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
377                                 selfballoon_min_usable_mb);
378
379 static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
380                                                struct device_attribute *attr,
381                                                const char *buf,
382                                                size_t count)
383 {
384         unsigned long val;
385         int err;
386
387         if (!capable(CAP_SYS_ADMIN))
388                 return -EPERM;
389         err = strict_strtoul(buf, 10, &val);
390         if (err || val == 0)
391                 return -EINVAL;
392         selfballoon_min_usable_mb = val;
393         return count;
394 }
395
396 static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
397                    show_selfballoon_min_usable_mb,
398                    store_selfballoon_min_usable_mb);
399
400
401 #ifdef CONFIG_FRONTSWAP
402 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
403
404 static ssize_t store_frontswap_selfshrinking(struct device *dev,
405                                              struct device_attribute *attr,
406                                              const char *buf,
407                                              size_t count)
408 {
409         bool was_enabled = frontswap_selfshrinking;
410         unsigned long tmp;
411         int err;
412
413         if (!capable(CAP_SYS_ADMIN))
414                 return -EPERM;
415         err = strict_strtoul(buf, 10, &tmp);
416         if (err || ((tmp != 0) && (tmp != 1)))
417                 return -EINVAL;
418         frontswap_selfshrinking = !!tmp;
419         if (!was_enabled && !xen_selfballooning_enabled &&
420              frontswap_selfshrinking)
421                 schedule_delayed_work(&selfballoon_worker,
422                         selfballoon_interval * HZ);
423
424         return count;
425 }
426
427 static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
428                    show_frontswap_selfshrinking, store_frontswap_selfshrinking);
429
430 SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
431
432 static ssize_t store_frontswap_inertia(struct device *dev,
433                                        struct device_attribute *attr,
434                                        const char *buf,
435                                        size_t count)
436 {
437         unsigned long val;
438         int err;
439
440         if (!capable(CAP_SYS_ADMIN))
441                 return -EPERM;
442         err = strict_strtoul(buf, 10, &val);
443         if (err || val == 0)
444                 return -EINVAL;
445         frontswap_inertia = val;
446         frontswap_inertia_counter = val;
447         return count;
448 }
449
450 static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
451                    show_frontswap_inertia, store_frontswap_inertia);
452
453 SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
454
455 static ssize_t store_frontswap_hysteresis(struct device *dev,
456                                           struct device_attribute *attr,
457                                           const char *buf,
458                                           size_t count)
459 {
460         unsigned long val;
461         int err;
462
463         if (!capable(CAP_SYS_ADMIN))
464                 return -EPERM;
465         err = strict_strtoul(buf, 10, &val);
466         if (err || val == 0)
467                 return -EINVAL;
468         frontswap_hysteresis = val;
469         return count;
470 }
471
472 static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
473                    show_frontswap_hysteresis, store_frontswap_hysteresis);
474
475 #endif /* CONFIG_FRONTSWAP */
476
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,
487 #endif
488         NULL
489 };
490
491 static struct attribute_group selfballoon_group = {
492         .name = "selfballoon",
493         .attrs = selfballoon_attrs
494 };
495 #endif
496
497 int register_xen_selfballooning(struct device *dev)
498 {
499         int error = -1;
500
501 #ifdef CONFIG_SYSFS
502         error = sysfs_create_group(&dev->kobj, &selfballoon_group);
503 #endif
504         return error;
505 }
506 EXPORT_SYMBOL(register_xen_selfballooning);
507
508 static int __init xen_selfballoon_init(void)
509 {
510         bool enable = false;
511
512         if (!xen_domain())
513                 return -ENODEV;
514
515         if (xen_initial_domain()) {
516                 pr_info("xen/balloon: Xen selfballooning driver "
517                                 "disabled for domain0.\n");
518                 return -ENODEV;
519         }
520
521         xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
522         if (xen_selfballooning_enabled) {
523                 pr_info("xen/balloon: Initializing Xen "
524                                         "selfballooning driver.\n");
525                 enable = true;
526         }
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");
532                 enable = true;
533         }
534 #endif
535         if (!enable)
536                 return -ENODEV;
537
538         schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
539
540         return 0;
541 }
542
543 subsys_initcall(xen_selfballoon_init);
544
545 MODULE_LICENSE("GPL");