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