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. Note, that selfballooning should be disabled by default
  57  * if frontswap is not configured.  Similarly selfballooning should be enabled
  58  * by default if frontswap is configured and can be disabled with the
  59  * "tmem.selfballooning=0" kernel boot option.  Finally, when frontswap is
  60  * configured, frontswap-selfshrinking can be disabled  with the
  61  * "tmem.selfshrink=0" kernel boot option.
  62  *
  63  * Selfballooning is disallowed in domain0 and force-disabled.
  64  *
  65  */
  66
  67 #include <linux/kernel.h>
  68 #include <linux/bootmem.h>
  69 #include <linux/swap.h>
  70 #include <linux/mm.h>
  71 #include <linux/mman.h>
  72 #include <linux/module.h>
  73 #include <linux/workqueue.h>
  74 #include <linux/device.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 /*
  97  * Minimum usable RAM in MB for selfballooning target for balloon.
  98  * If non-zero, it is added to totalreserve_pages and self-ballooning
  99  * will not balloon below the sum.  If zero, a piecewise linear function
 100  * is calculated as a minimum and added to totalreserve_pages.  Note that
 101  * setting this value indiscriminately may cause OOMs and crashes.
 102  */
 103 static unsigned int selfballoon_min_usable_mb;
 104
 105 /*
 106  * Amount of RAM in MB to add to the target number of pages.
 107  * Can be used to reserve some more room for caches and the like.
 108  */
 109 static unsigned int selfballoon_reserved_mb;
 110
 111 static void selfballoon_process(struct work_struct *work);
 112 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
 113
 114 #ifdef CONFIG_FRONTSWAP
 115 #include <linux/frontswap.h>
 116
 117 /* Enable/disable with sysfs. */
 118 static bool frontswap_selfshrinking __read_mostly;
 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 #endif /* CONFIG_FRONTSWAP */
 174
 175 #define MB2PAGES(mb)    ((mb) << (20 - PAGE_SHIFT))
 176
 177 /*
 178  * Use current balloon size, the goal (vm_committed_as), and hysteresis
 179  * parameters to set a new target balloon size
 180  */
 181 static void selfballoon_process(struct work_struct *work)
 182 {
 183         unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
 184         unsigned long useful_pages;
 185         bool reset_timer = false;
 186
 187         if (xen_selfballooning_enabled) {
 188                 cur_pages = totalram_pages;
 189                 tgt_pages = cur_pages; /* default is no change */
 190                 goal_pages = vm_memory_committed() +
 191                                 totalreserve_pages +
 192                                 MB2PAGES(selfballoon_reserved_mb);
 193 #ifdef CONFIG_FRONTSWAP
 194                 /* allow space for frontswap pages to be repatriated */
 195                 if (frontswap_selfshrinking && frontswap_enabled)
 196                         goal_pages += frontswap_curr_pages();
 197 #endif
 198                 if (cur_pages > goal_pages)
 199                         tgt_pages = cur_pages -
 200                                 ((cur_pages - goal_pages) /
 201                                   selfballoon_downhysteresis);
 202                 else if (cur_pages < goal_pages)
 203                         tgt_pages = cur_pages +
 204                                 ((goal_pages - cur_pages) /
 205                                   selfballoon_uphysteresis);
 206                 /* else if cur_pages == goal_pages, no change */
 207                 useful_pages = max_pfn - totalreserve_pages;
 208                 if (selfballoon_min_usable_mb != 0)
 209                         floor_pages = totalreserve_pages +
 210                                         MB2PAGES(selfballoon_min_usable_mb);
 211                 /* piecewise linear function ending in ~3% slope */
 212                 else if (useful_pages < MB2PAGES(16))
 213                         floor_pages = max_pfn; /* not worth ballooning */
 214                 else if (useful_pages < MB2PAGES(64))
 215                         floor_pages = totalreserve_pages + MB2PAGES(16) +
 216                                         ((useful_pages - MB2PAGES(16)) >> 1);
 217                 else if (useful_pages < MB2PAGES(512))
 218                         floor_pages = totalreserve_pages + MB2PAGES(40) +
 219                                         ((useful_pages - MB2PAGES(40)) >> 3);
 220                 else /* useful_pages >= MB2PAGES(512) */
 221                         floor_pages = totalreserve_pages + MB2PAGES(99) +
 222                                         ((useful_pages - MB2PAGES(99)) >> 5);
 223                 if (tgt_pages < floor_pages)
 224                         tgt_pages = floor_pages;
 225                 balloon_set_new_target(tgt_pages +
 226                         balloon_stats.current_pages - totalram_pages);
 227                 reset_timer = true;
 228         }
 229 #ifdef CONFIG_FRONTSWAP
 230         if (frontswap_selfshrinking && frontswap_enabled) {
 231                 frontswap_selfshrink();
 232                 reset_timer = true;
 233         }
 234 #endif
 235         if (reset_timer)
 236                 schedule_delayed_work(&selfballoon_worker,
 237                         selfballoon_interval * HZ);
 238 }
 239
 240 #ifdef CONFIG_SYSFS
 241
 242 #include <linux/capability.h>
 243
 244 #define SELFBALLOON_SHOW(name, format, args...)                         \
 245         static ssize_t show_##name(struct device *dev,  \
 246                                           struct device_attribute *attr, \
 247                                           char *buf) \
 248         { \
 249                 return sprintf(buf, format, ##args); \
 250         }
 251
 252 SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
 253
 254 static ssize_t store_selfballooning(struct device *dev,
 255                             struct device_attribute *attr,
 256                             const char *buf,
 257                             size_t count)
 258 {
 259         bool was_enabled = xen_selfballooning_enabled;
 260         unsigned long tmp;
 261         int err;
 262
 263         if (!capable(CAP_SYS_ADMIN))
 264                 return -EPERM;
 265
 266         err = strict_strtoul(buf, 10, &tmp);
 267         if (err || ((tmp != 0) && (tmp != 1)))
 268                 return -EINVAL;
 269
 270         xen_selfballooning_enabled = !!tmp;
 271         if (!was_enabled && xen_selfballooning_enabled)
 272                 schedule_delayed_work(&selfballoon_worker,
 273                         selfballoon_interval * HZ);
 274
 275         return count;
 276 }
 277
 278 static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
 279                    show_selfballooning, store_selfballooning);
 280
 281 SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
 282
 283 static ssize_t store_selfballoon_interval(struct device *dev,
 284                                           struct device_attribute *attr,
 285                                           const char *buf,
 286                                           size_t count)
 287 {
 288         unsigned long val;
 289         int err;
 290
 291         if (!capable(CAP_SYS_ADMIN))
 292                 return -EPERM;
 293         err = strict_strtoul(buf, 10, &val);
 294         if (err || val == 0)
 295                 return -EINVAL;
 296         selfballoon_interval = val;
 297         return count;
 298 }
 299
 300 static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
 301                    show_selfballoon_interval, store_selfballoon_interval);
 302
 303 SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
 304
 305 static ssize_t store_selfballoon_downhys(struct device *dev,
 306                                          struct device_attribute *attr,
 307                                          const char *buf,
 308                                          size_t count)
 309 {
 310         unsigned long val;
 311         int err;
 312
 313         if (!capable(CAP_SYS_ADMIN))
 314                 return -EPERM;
 315         err = strict_strtoul(buf, 10, &val);
 316         if (err || val == 0)
 317                 return -EINVAL;
 318         selfballoon_downhysteresis = val;
 319         return count;
 320 }
 321
 322 static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
 323                    show_selfballoon_downhys, store_selfballoon_downhys);
 324
 325
 326 SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
 327
 328 static ssize_t store_selfballoon_uphys(struct device *dev,
 329                                        struct device_attribute *attr,
 330                                        const char *buf,
 331                                        size_t count)
 332 {
 333         unsigned long val;
 334         int err;
 335
 336         if (!capable(CAP_SYS_ADMIN))
 337                 return -EPERM;
 338         err = strict_strtoul(buf, 10, &val);
 339         if (err || val == 0)
 340                 return -EINVAL;
 341         selfballoon_uphysteresis = val;
 342         return count;
 343 }
 344
 345 static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
 346                    show_selfballoon_uphys, store_selfballoon_uphys);
 347
 348 SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
 349                                 selfballoon_min_usable_mb);
 350
 351 static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
 352                                                struct device_attribute *attr,
 353                                                const char *buf,
 354                                                size_t count)
 355 {
 356         unsigned long val;
 357         int err;
 358
 359         if (!capable(CAP_SYS_ADMIN))
 360                 return -EPERM;
 361         err = strict_strtoul(buf, 10, &val);
 362         if (err || val == 0)
 363                 return -EINVAL;
 364         selfballoon_min_usable_mb = val;
 365         return count;
 366 }
 367
 368 static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
 369                    show_selfballoon_min_usable_mb,
 370                    store_selfballoon_min_usable_mb);
 371
 372 SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
 373                                 selfballoon_reserved_mb);
 374
 375 static ssize_t store_selfballoon_reserved_mb(struct device *dev,
 376                                              struct device_attribute *attr,
 377                                              const char *buf,
 378                                              size_t count)
 379 {
 380         unsigned long val;
 381         int err;
 382
 383         if (!capable(CAP_SYS_ADMIN))
 384                 return -EPERM;
 385         err = strict_strtoul(buf, 10, &val);
 386         if (err || val == 0)
 387                 return -EINVAL;
 388         selfballoon_reserved_mb = val;
 389         return count;
 390 }
 391
 392 static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
 393                    show_selfballoon_reserved_mb,
 394                    store_selfballoon_reserved_mb);
 395
 396
 397 #ifdef CONFIG_FRONTSWAP
 398 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
 399
 400 static ssize_t store_frontswap_selfshrinking(struct device *dev,
 401                                              struct device_attribute *attr,
 402                                              const char *buf,
 403                                              size_t count)
 404 {
 405         bool was_enabled = frontswap_selfshrinking;
 406         unsigned long tmp;
 407         int err;
 408
 409         if (!capable(CAP_SYS_ADMIN))
 410                 return -EPERM;
 411         err = strict_strtoul(buf, 10, &tmp);
 412         if (err || ((tmp != 0) && (tmp != 1)))
 413                 return -EINVAL;
 414         frontswap_selfshrinking = !!tmp;
 415         if (!was_enabled && !xen_selfballooning_enabled &&
 416              frontswap_selfshrinking)
 417                 schedule_delayed_work(&selfballoon_worker,
 418                         selfballoon_interval * HZ);
 419
 420         return count;
 421 }
 422
 423 static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
 424                    show_frontswap_selfshrinking, store_frontswap_selfshrinking);
 425
 426 SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
 427
 428 static ssize_t store_frontswap_inertia(struct device *dev,
 429                                        struct device_attribute *attr,
 430                                        const char *buf,
 431                                        size_t count)
 432 {
 433         unsigned long val;
 434         int err;
 435
 436         if (!capable(CAP_SYS_ADMIN))
 437                 return -EPERM;
 438         err = strict_strtoul(buf, 10, &val);
 439         if (err || val == 0)
 440                 return -EINVAL;
 441         frontswap_inertia = val;
 442         frontswap_inertia_counter = val;
 443         return count;
 444 }
 445
 446 static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
 447                    show_frontswap_inertia, store_frontswap_inertia);
 448
 449 SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
 450
 451 static ssize_t store_frontswap_hysteresis(struct device *dev,
 452                                           struct device_attribute *attr,
 453                                           const char *buf,
 454                                           size_t count)
 455 {
 456         unsigned long val;
 457         int err;
 458
 459         if (!capable(CAP_SYS_ADMIN))
 460                 return -EPERM;
 461         err = strict_strtoul(buf, 10, &val);
 462         if (err || val == 0)
 463                 return -EINVAL;
 464         frontswap_hysteresis = val;
 465         return count;
 466 }
 467
 468 static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
 469                    show_frontswap_hysteresis, store_frontswap_hysteresis);
 470
 471 #endif /* CONFIG_FRONTSWAP */
 472
 473 static struct attribute *selfballoon_attrs[] = {
 474         &dev_attr_selfballooning.attr,
 475         &dev_attr_selfballoon_interval.attr,
 476         &dev_attr_selfballoon_downhysteresis.attr,
 477         &dev_attr_selfballoon_uphysteresis.attr,
 478         &dev_attr_selfballoon_min_usable_mb.attr,
 479         &dev_attr_selfballoon_reserved_mb.attr,
 480 #ifdef CONFIG_FRONTSWAP
 481         &dev_attr_frontswap_selfshrinking.attr,
 482         &dev_attr_frontswap_hysteresis.attr,
 483         &dev_attr_frontswap_inertia.attr,
 484 #endif
 485         NULL
 486 };
 487
 488 static const struct attribute_group selfballoon_group = {
 489         .name = "selfballoon",
 490         .attrs = selfballoon_attrs
 491 };
 492 #endif
 493
 494 int register_xen_selfballooning(struct device *dev)
 495 {
 496         int error = -1;
 497
 498 #ifdef CONFIG_SYSFS
 499         error = sysfs_create_group(&dev->kobj, &selfballoon_group);
 500 #endif
 501         return error;
 502 }
 503 EXPORT_SYMBOL(register_xen_selfballooning);
 504
 505 int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
 506 {
 507         bool enable = false;
 508
 509         if (!xen_domain())
 510                 return -ENODEV;
 511
 512         if (xen_initial_domain()) {
 513                 pr_info("xen/balloon: Xen selfballooning driver "
 514                                 "disabled for domain0.\n");
 515                 return -ENODEV;
 516         }
 517
 518         xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
 519         if (xen_selfballooning_enabled) {
 520                 pr_info("xen/balloon: Initializing Xen "
 521                                         "selfballooning driver.\n");
 522                 enable = true;
 523         }
 524 #ifdef CONFIG_FRONTSWAP
 525         frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
 526         if (frontswap_selfshrinking) {
 527                 pr_info("xen/balloon: Initializing frontswap "
 528                                         "selfshrinking driver.\n");
 529                 enable = true;
 530         }
 531 #endif
 532         if (!enable)
 533                 return -ENODEV;
 534
 535         schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
 536
 537         return 0;
 538 }
 539 EXPORT_SYMBOL(xen_selfballoon_init);