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/mm.h>
  72 #include <linux/mman.h>
  73 #include <linux/module.h>
  74 #include <linux/workqueue.h>
  75 #include <xen/balloon.h>
  76 #include <xen/tmem.h>
  77 #include <xen/xen.h>
  78
  79 /* Enable/disable with sysfs. */
  80 static int xen_selfballooning_enabled __read_mostly;
  81
  82 /*
  83  * Controls rate at which memory target (this iteration) approaches
  84  * ultimate goal when memory need is increasing (up-hysteresis) or
  85  * decreasing (down-hysteresis). Higher values of hysteresis cause
  86  * slower increases/decreases. The default values for the various
  87  * parameters were deemed reasonable by experimentation, may be
  88  * workload-dependent, and can all be adjusted via sysfs.
  89  */
  90 static unsigned int selfballoon_downhysteresis __read_mostly = 8;
  91 static unsigned int selfballoon_uphysteresis __read_mostly = 1;
  92
  93 /* In HZ, controls frequency of worker invocation. */
  94 static unsigned int selfballoon_interval __read_mostly = 5;
  95
  96 static void selfballoon_process(struct work_struct *work);
  97 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
  98
  99 #ifdef CONFIG_FRONTSWAP
 100 #include <linux/frontswap.h>
 101
 102 /* Enable/disable with sysfs. */
 103 static bool frontswap_selfshrinking __read_mostly;
 104
 105 /* Enable/disable with kernel boot option. */
 106 static bool use_frontswap_selfshrink __initdata = true;
 107
 108 /*
 109  * The default values for the following parameters were deemed reasonable
 110  * by experimentation, may be workload-dependent, and can all be
 111  * adjusted via sysfs.
 112  */
 113
 114 /* Control rate for frontswap shrinking. Higher hysteresis is slower. */
 115 static unsigned int frontswap_hysteresis __read_mostly = 20;
 116
 117 /*
 118  * Number of selfballoon worker invocations to wait before observing that
 119  * frontswap selfshrinking should commence. Note that selfshrinking does
 120  * not use a separate worker thread.
 121  */
 122 static unsigned int frontswap_inertia __read_mostly = 3;
 123
 124 /* Countdown to next invocation of frontswap_shrink() */
 125 static unsigned long frontswap_inertia_counter;
 126
 127 /*
 128  * Invoked by the selfballoon worker thread, uses current number of pages
 129  * in frontswap (frontswap_curr_pages()), previous status, and control
 130  * values (hysteresis and inertia) to determine if frontswap should be
 131  * shrunk and what the new frontswap size should be.  Note that
 132  * frontswap_shrink is essentially a partial swapoff that immediately
 133  * transfers pages from the "swap device" (frontswap) back into kernel
 134  * RAM; despite the name, frontswap "shrinking" is very different from
 135  * the "shrinker" interface used by the kernel MM subsystem to reclaim
 136  * memory.
 137  */
 138 static void frontswap_selfshrink(void)
 139 {
 140         static unsigned long cur_frontswap_pages;
 141         static unsigned long last_frontswap_pages;
 142         static unsigned long tgt_frontswap_pages;
 143
 144         last_frontswap_pages = cur_frontswap_pages;
 145         cur_frontswap_pages = frontswap_curr_pages();
 146         if (!cur_frontswap_pages ||
 147                         (cur_frontswap_pages > last_frontswap_pages)) {
 148                 frontswap_inertia_counter = frontswap_inertia;
 149                 return;
 150         }
 151         if (frontswap_inertia_counter && --frontswap_inertia_counter)
 152                 return;
 153         if (cur_frontswap_pages <= frontswap_hysteresis)
 154                 tgt_frontswap_pages = 0;
 155         else
 156                 tgt_frontswap_pages = cur_frontswap_pages -
 157                         (cur_frontswap_pages / frontswap_hysteresis);
 158         frontswap_shrink(tgt_frontswap_pages);
 159 }
 160
 161 static int __init xen_nofrontswap_selfshrink_setup(char *s)
 162 {
 163         use_frontswap_selfshrink = false;
 164         return 1;
 165 }
 166
 167 __setup("noselfshrink", xen_nofrontswap_selfshrink_setup);
 168
 169 /* Disable with kernel boot option. */
 170 static bool use_selfballooning __initdata = true;
 171
 172 static int __init xen_noselfballooning_setup(char *s)
 173 {
 174         use_selfballooning = false;
 175         return 1;
 176 }
 177
 178 __setup("noselfballooning", xen_noselfballooning_setup);
 179 #else /* !CONFIG_FRONTSWAP */
 180 /* Enable with kernel boot option. */
 181 static bool use_selfballooning __initdata = false;
 182
 183 static int __init xen_selfballooning_setup(char *s)
 184 {
 185         use_selfballooning = true;
 186         return 1;
 187 }
 188
 189 __setup("selfballooning", xen_selfballooning_setup);
 190 #endif /* CONFIG_FRONTSWAP */
 191
 192 /*
 193  * Use current balloon size, the goal (vm_committed_as), and hysteresis
 194  * parameters to set a new target balloon size
 195  */
 196 static void selfballoon_process(struct work_struct *work)
 197 {
 198         unsigned long cur_pages, goal_pages, tgt_pages;
 199         bool reset_timer = false;
 200
 201         if (xen_selfballooning_enabled) {
 202                 cur_pages = balloon_stats.current_pages;
 203                 tgt_pages = cur_pages; /* default is no change */
 204                 goal_pages = percpu_counter_read_positive(&vm_committed_as) +
 205                         balloon_stats.current_pages - totalram_pages;
 206 #ifdef CONFIG_FRONTSWAP
 207                 /* allow space for frontswap pages to be repatriated */
 208                 if (frontswap_selfshrinking && frontswap_enabled)
 209                         goal_pages += frontswap_curr_pages();
 210 #endif
 211                 if (cur_pages > goal_pages)
 212                         tgt_pages = cur_pages -
 213                                 ((cur_pages - goal_pages) /
 214                                   selfballoon_downhysteresis);
 215                 else if (cur_pages < goal_pages)
 216                         tgt_pages = cur_pages +
 217                                 ((goal_pages - cur_pages) /
 218                                   selfballoon_uphysteresis);
 219                 /* else if cur_pages == goal_pages, no change */
 220                 balloon_set_new_target(tgt_pages);
 221                 reset_timer = true;
 222         }
 223 #ifdef CONFIG_FRONTSWAP
 224         if (frontswap_selfshrinking && frontswap_enabled) {
 225                 frontswap_selfshrink();
 226                 reset_timer = true;
 227         }
 228 #endif
 229         if (reset_timer)
 230                 schedule_delayed_work(&selfballoon_worker,
 231                         selfballoon_interval * HZ);
 232 }
 233
 234 #ifdef CONFIG_SYSFS
 235
 236 #include <linux/sysdev.h>
 237 #include <linux/capability.h>
 238
 239 #define SELFBALLOON_SHOW(name, format, args...)                         \
 240         static ssize_t show_##name(struct sys_device *dev,      \
 241                                            struct sysdev_attribute *attr, \
 242                                            char *buf) \
 243         { \
 244                 return sprintf(buf, format, ##args); \
 245         }
 246
 247 SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
 248
 249 static ssize_t store_selfballooning(struct sys_device *dev,
 250                             struct sysdev_attribute *attr,
 251                             const char *buf,
 252                             size_t count)
 253 {
 254         bool was_enabled = xen_selfballooning_enabled;
 255         unsigned long tmp;
 256         int err;
 257
 258         if (!capable(CAP_SYS_ADMIN))
 259                 return -EPERM;
 260
 261         err = strict_strtoul(buf, 10, &tmp);
 262         if (err || ((tmp != 0) && (tmp != 1)))
 263                 return -EINVAL;
 264
 265         xen_selfballooning_enabled = !!tmp;
 266         if (!was_enabled && xen_selfballooning_enabled)
 267                 schedule_delayed_work(&selfballoon_worker,
 268                         selfballoon_interval * HZ);
 269
 270         return count;
 271 }
 272
 273 static SYSDEV_ATTR(selfballooning, S_IRUGO | S_IWUSR,
 274                    show_selfballooning, store_selfballooning);
 275
 276 SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
 277
 278 static ssize_t store_selfballoon_interval(struct sys_device *dev,
 279                                           struct sysdev_attribute *attr,
 280                                           const char *buf,
 281                                           size_t count)
 282 {
 283         unsigned long val;
 284         int err;
 285
 286         if (!capable(CAP_SYS_ADMIN))
 287                 return -EPERM;
 288         err = strict_strtoul(buf, 10, &val);
 289         if (err || val == 0)
 290                 return -EINVAL;
 291         selfballoon_interval = val;
 292         return count;
 293 }
 294
 295 static SYSDEV_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
 296                    show_selfballoon_interval, store_selfballoon_interval);
 297
 298 SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
 299
 300 static ssize_t store_selfballoon_downhys(struct sys_device *dev,
 301                                          struct sysdev_attribute *attr,
 302                                          const char *buf,
 303                                          size_t count)
 304 {
 305         unsigned long val;
 306         int err;
 307
 308         if (!capable(CAP_SYS_ADMIN))
 309                 return -EPERM;
 310         err = strict_strtoul(buf, 10, &val);
 311         if (err || val == 0)
 312                 return -EINVAL;
 313         selfballoon_downhysteresis = val;
 314         return count;
 315 }
 316
 317 static SYSDEV_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
 318                    show_selfballoon_downhys, store_selfballoon_downhys);
 319
 320
 321 SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
 322
 323 static ssize_t store_selfballoon_uphys(struct sys_device *dev,
 324                                        struct sysdev_attribute *attr,
 325                                        const char *buf,
 326                                        size_t count)
 327 {
 328         unsigned long val;
 329         int err;
 330
 331         if (!capable(CAP_SYS_ADMIN))
 332                 return -EPERM;
 333         err = strict_strtoul(buf, 10, &val);
 334         if (err || val == 0)
 335                 return -EINVAL;
 336         selfballoon_uphysteresis = val;
 337         return count;
 338 }
 339
 340 static SYSDEV_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
 341                    show_selfballoon_uphys, store_selfballoon_uphys);
 342
 343 #ifdef CONFIG_FRONTSWAP
 344 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
 345
 346 static ssize_t store_frontswap_selfshrinking(struct sys_device *dev,
 347                                              struct sysdev_attribute *attr,
 348                                              const char *buf,
 349                                              size_t count)
 350 {
 351         bool was_enabled = frontswap_selfshrinking;
 352         unsigned long tmp;
 353         int err;
 354
 355         if (!capable(CAP_SYS_ADMIN))
 356                 return -EPERM;
 357         err = strict_strtoul(buf, 10, &tmp);
 358         if (err || ((tmp != 0) && (tmp != 1)))
 359                 return -EINVAL;
 360         frontswap_selfshrinking = !!tmp;
 361         if (!was_enabled && !xen_selfballooning_enabled &&
 362              frontswap_selfshrinking)
 363                 schedule_delayed_work(&selfballoon_worker,
 364                         selfballoon_interval * HZ);
 365
 366         return count;
 367 }
 368
 369 static SYSDEV_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
 370                    show_frontswap_selfshrinking, store_frontswap_selfshrinking);
 371
 372 SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
 373
 374 static ssize_t store_frontswap_inertia(struct sys_device *dev,
 375                                        struct sysdev_attribute *attr,
 376                                        const char *buf,
 377                                        size_t count)
 378 {
 379         unsigned long val;
 380         int err;
 381
 382         if (!capable(CAP_SYS_ADMIN))
 383                 return -EPERM;
 384         err = strict_strtoul(buf, 10, &val);
 385         if (err || val == 0)
 386                 return -EINVAL;
 387         frontswap_inertia = val;
 388         frontswap_inertia_counter = val;
 389         return count;
 390 }
 391
 392 static SYSDEV_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
 393                    show_frontswap_inertia, store_frontswap_inertia);
 394
 395 SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
 396
 397 static ssize_t store_frontswap_hysteresis(struct sys_device *dev,
 398                                           struct sysdev_attribute *attr,
 399                                           const char *buf,
 400                                           size_t count)
 401 {
 402         unsigned long val;
 403         int err;
 404
 405         if (!capable(CAP_SYS_ADMIN))
 406                 return -EPERM;
 407         err = strict_strtoul(buf, 10, &val);
 408         if (err || val == 0)
 409                 return -EINVAL;
 410         frontswap_hysteresis = val;
 411         return count;
 412 }
 413
 414 static SYSDEV_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
 415                    show_frontswap_hysteresis, store_frontswap_hysteresis);
 416
 417 #endif /* CONFIG_FRONTSWAP */
 418
 419 static struct attribute *selfballoon_attrs[] = {
 420         &attr_selfballooning.attr,
 421         &attr_selfballoon_interval.attr,
 422         &attr_selfballoon_downhysteresis.attr,
 423         &attr_selfballoon_uphysteresis.attr,
 424 #ifdef CONFIG_FRONTSWAP
 425         &attr_frontswap_selfshrinking.attr,
 426         &attr_frontswap_hysteresis.attr,
 427         &attr_frontswap_inertia.attr,
 428 #endif
 429         NULL
 430 };
 431
 432 static struct attribute_group selfballoon_group = {
 433         .name = "selfballoon",
 434         .attrs = selfballoon_attrs
 435 };
 436 #endif
 437
 438 int register_xen_selfballooning(struct sys_device *sysdev)
 439 {
 440         int error = -1;
 441
 442 #ifdef CONFIG_SYSFS
 443         error = sysfs_create_group(&sysdev->kobj, &selfballoon_group);
 444 #endif
 445         return error;
 446 }
 447 EXPORT_SYMBOL(register_xen_selfballooning);
 448
 449 static int __init xen_selfballoon_init(void)
 450 {
 451         bool enable = false;
 452
 453         if (!xen_domain())
 454                 return -ENODEV;
 455
 456         if (xen_initial_domain()) {
 457                 pr_info("xen/balloon: Xen selfballooning driver "
 458                                 "disabled for domain0.\n");
 459                 return -ENODEV;
 460         }
 461
 462         xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
 463         if (xen_selfballooning_enabled) {
 464                 pr_info("xen/balloon: Initializing Xen "
 465                                         "selfballooning driver.\n");
 466                 enable = true;
 467         }
 468 #ifdef CONFIG_FRONTSWAP
 469         frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
 470         if (frontswap_selfshrinking) {
 471                 pr_info("xen/balloon: Initializing frontswap "
 472                                         "selfshrinking driver.\n");
 473                 enable = true;
 474         }
 475 #endif
 476         if (!enable)
 477                 return -ENODEV;
 478
 479         schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
 480
 481         return 0;
 482 }
 483
 484 subsys_initcall(xen_selfballoon_init);
 485
 486 MODULE_LICENSE("GPL");