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 /*
 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  */
 112 static unsigned int selfballoon_reserved_mb;
 113
 114 static void selfballoon_process(struct work_struct *work);
 115 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
 116
 117 #ifdef CONFIG_FRONTSWAP
 118 #include <linux/frontswap.h>
 119
 120 /* Enable/disable with sysfs. */
 121 static bool frontswap_selfshrinking __read_mostly;
 122
 123 /* Enable/disable with kernel boot option. */
 124 static 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. */
 133 static 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  */
 140 static unsigned int frontswap_inertia __read_mostly = 3;
 141
 142 /* Countdown to next invocation of frontswap_shrink() */
 143 static 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  */
 156 static 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
 179 static 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. */
 188 static bool use_selfballooning __initdata = true;
 189
 190 static 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. */
 199 static bool use_selfballooning __initdata = false;
 200
 201 static 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  */
 216 static 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
 287 SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
 288
 289 static 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
 313 static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
 314                    show_selfballooning, store_selfballooning);
 315
 316 SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
 317
 318 static 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
 335 static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
 336                    show_selfballoon_interval, store_selfballoon_interval);
 337
 338 SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
 339
 340 static 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
 357 static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
 358                    show_selfballoon_downhys, store_selfballoon_downhys);
 359
 360
 361 SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
 362
 363 static 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
 380 static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
 381                    show_selfballoon_uphys, store_selfballoon_uphys);
 382
 383 SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
 384                                 selfballoon_min_usable_mb);
 385
 386 static 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
 403 static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
 404                    show_selfballoon_min_usable_mb,
 405                    store_selfballoon_min_usable_mb);
 406
 407 SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
 408                                 selfballoon_reserved_mb);
 409
 410 static 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
 427 static 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
 433 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
 434
 435 static 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
 458 static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
 459                    show_frontswap_selfshrinking, store_frontswap_selfshrinking);
 460
 461 SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
 462
 463 static 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
 481 static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
 482                    show_frontswap_inertia, store_frontswap_inertia);
 483
 484 SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
 485
 486 static 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
 503 static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
 504                    show_frontswap_hysteresis, store_frontswap_hysteresis);
 505
 506 #endif /* CONFIG_FRONTSWAP */
 507
 508 static 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
 523 static const struct attribute_group selfballoon_group = {
 524         .name = "selfballoon",
 525         .attrs = selfballoon_attrs
 526 };
 527 #endif
 528
 529 int 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 }
 538 EXPORT_SYMBOL(register_xen_selfballooning);
 539
 540 static 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
 575 subsys_initcall(xen_selfballoon_init);
 576
 577 MODULE_LICENSE("GPL");