drivers/xen/xen-selfballoon.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /******************************************************************************
   3  * Xen selfballoon driver (and optional frontswap self-shrinking driver)
   4  *
   5  * Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.
   6  *
   7  * This code complements the cleancache and frontswap patchsets to optimize
   8  * support for Xen Transcendent Memory ("tmem").  The policy it implements
   9  * is rudimentary and will likely improve over time, but it does work well
  10  * enough today.
  11  *
  12  * Two functionalities are implemented here which both use "control theory"
  13  * (feedback) to optimize memory utilization. In a virtualized environment
  14  * such as Xen, RAM is often a scarce resource and we would like to ensure
  15  * that each of a possibly large number of virtual machines is using RAM
  16  * efficiently, i.e. using as little as possible when under light load
  17  * and obtaining as much as possible when memory demands are high.
  18  * Since RAM needs vary highly dynamically and sometimes dramatically,
  19  * "hysteresis" is used, that is, memory target is determined not just
  20  * on current data but also on past data stored in the system.
  21  *
  22  * "Selfballooning" creates memory pressure by managing the Xen balloon
  23  * driver to decrease and increase available kernel memory, driven
  24  * largely by the target value of "Committed_AS" (see /proc/meminfo).
  25  * Since Committed_AS does not account for clean mapped pages (i.e. pages
  26  * in RAM that are identical to pages on disk), selfballooning has the
  27  * affect of pushing less frequently used clean pagecache pages out of
  28  * kernel RAM and, presumably using cleancache, into Xen tmem where
  29  * Xen can more efficiently optimize RAM utilization for such pages.
  30  *
  31  * When kernel memory demand unexpectedly increases faster than Xen, via
  32  * the selfballoon driver, is able to (or chooses to) provide usable RAM,
  33  * the kernel may invoke swapping.  In most cases, frontswap is able
  34  * to absorb this swapping into Xen tmem.  However, due to the fact
  35  * that the kernel swap subsystem assumes swapping occurs to a disk,
  36  * swapped pages may sit on the disk for a very long time; even if
  37  * the kernel knows the page will never be used again.  This is because
  38  * the disk space costs very little and can be overwritten when
  39  * necessary.  When such stale pages are in frontswap, however, they
  40  * are taking up valuable real estate.  "Frontswap selfshrinking" works
  41  * to resolve this:  When frontswap activity is otherwise stable
  42  * and the guest kernel is not under memory pressure, the "frontswap
  43  * selfshrinking" accounts for this by providing pressure to remove some
  44  * pages from frontswap and return them to kernel memory.
  45  *
  46  * For both "selfballooning" and "frontswap-selfshrinking", a worker
  47  * thread is used and sysfs tunables are provided to adjust the frequency
  48  * and rate of adjustments to achieve the goal, as well as to disable one
  49  * or both functions independently.
  50  *
  51  * While some argue that this functionality can and should be implemented
  52  * in userspace, it has been observed that bad things happen (e.g. OOMs).
  53  *
  54  * System configuration note: Selfballooning should not be enabled on
  55  * systems without a sufficiently large swap device configured; for best
  56  * results, it is recommended that total swap be increased by the size
  57  * of the guest memory. Note, that selfballooning should be disabled by default
  58  * if frontswap is not configured.  Similarly selfballooning should be enabled
  59  * by default if frontswap is configured and can be disabled with the
  60  * "tmem.selfballooning=0" kernel boot option.  Finally, when frontswap is
  61  * configured, frontswap-selfshrinking can be disabled  with the
  62  * "tmem.selfshrink=0" kernel boot option.
  63  *
  64  * Selfballooning is disallowed in domain0 and force-disabled.
  65  *
  66  */
  67
  68 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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/workqueue.h>
  76 #include <linux/device.h>
  77 #include <xen/balloon.h>
  78 #include <xen/tmem.h>
  79 #include <xen/xen.h>
  80
  81 /* Enable/disable with sysfs. */
  82 static int xen_selfballooning_enabled __read_mostly;
  83
  84 /*
  85  * Controls rate at which memory target (this iteration) approaches
  86  * ultimate goal when memory need is increasing (up-hysteresis) or
  87  * decreasing (down-hysteresis). Higher values of hysteresis cause
  88  * slower increases/decreases. The default values for the various
  89  * parameters were deemed reasonable by experimentation, may be
  90  * workload-dependent, and can all be adjusted via sysfs.
  91  */
  92 static unsigned int selfballoon_downhysteresis __read_mostly = 8;
  93 static unsigned int selfballoon_uphysteresis __read_mostly = 1;
  94
  95 /* In HZ, controls frequency of worker invocation. */
  96 static unsigned int selfballoon_interval __read_mostly = 5;
  97
  98 /*
  99  * Minimum usable RAM in MB for selfballooning target for balloon.
 100  * If non-zero, it is added to totalreserve_pages and self-ballooning
 101  * will not balloon below the sum.  If zero, a piecewise linear function
 102  * is calculated as a minimum and added to totalreserve_pages.  Note that
 103  * setting this value indiscriminately may cause OOMs and crashes.
 104  */
 105 static unsigned int selfballoon_min_usable_mb;
 106
 107 /*
 108  * Amount of RAM in MB to add to the target number of pages.
 109  * Can be used to reserve some more room for caches and the like.
 110  */
 111 static unsigned int selfballoon_reserved_mb;
 112
 113 static void selfballoon_process(struct work_struct *work);
 114 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
 115
 116 #ifdef CONFIG_FRONTSWAP
 117 #include <linux/frontswap.h>
 118
 119 /* Enable/disable with sysfs. */
 120 static bool frontswap_selfshrinking __read_mostly;
 121
 122 /*
 123  * The default values for the following parameters were deemed reasonable
 124  * by experimentation, may be workload-dependent, and can all be
 125  * adjusted via sysfs.
 126  */
 127
 128 /* Control rate for frontswap shrinking. Higher hysteresis is slower. */
 129 static unsigned int frontswap_hysteresis __read_mostly = 20;
 130
 131 /*
 132  * Number of selfballoon worker invocations to wait before observing that
 133  * frontswap selfshrinking should commence. Note that selfshrinking does
 134  * not use a separate worker thread.
 135  */
 136 static unsigned int frontswap_inertia __read_mostly = 3;
 137
 138 /* Countdown to next invocation of frontswap_shrink() */
 139 static unsigned long frontswap_inertia_counter;
 140
 141 /*
 142  * Invoked by the selfballoon worker thread, uses current number of pages
 143  * in frontswap (frontswap_curr_pages()), previous status, and control
 144  * values (hysteresis and inertia) to determine if frontswap should be
 145  * shrunk and what the new frontswap size should be.  Note that
 146  * frontswap_shrink is essentially a partial swapoff that immediately
 147  * transfers pages from the "swap device" (frontswap) back into kernel
 148  * RAM; despite the name, frontswap "shrinking" is very different from
 149  * the "shrinker" interface used by the kernel MM subsystem to reclaim
 150  * memory.
 151  */
 152 static void frontswap_selfshrink(void)
 153 {
 154         static unsigned long cur_frontswap_pages;
 155         unsigned long last_frontswap_pages;
 156         unsigned long tgt_frontswap_pages;
 157
 158         last_frontswap_pages = cur_frontswap_pages;
 159         cur_frontswap_pages = frontswap_curr_pages();
 160         if (!cur_frontswap_pages ||
 161                         (cur_frontswap_pages > last_frontswap_pages)) {
 162                 frontswap_inertia_counter = frontswap_inertia;
 163                 return;
 164         }
 165         if (frontswap_inertia_counter && --frontswap_inertia_counter)
 166                 return;
 167         if (cur_frontswap_pages <= frontswap_hysteresis)
 168                 tgt_frontswap_pages = 0;
 169         else
 170                 tgt_frontswap_pages = cur_frontswap_pages -
 171                         (cur_frontswap_pages / frontswap_hysteresis);
 172         frontswap_shrink(tgt_frontswap_pages);
 173         frontswap_inertia_counter = frontswap_inertia;
 174 }
 175
 176 #endif /* CONFIG_FRONTSWAP */
 177
 178 #define MB2PAGES(mb)    ((mb) << (20 - PAGE_SHIFT))
 179 #define PAGES2MB(pages) ((pages) >> (20 - PAGE_SHIFT))
 180
 181 /*
 182  * Use current balloon size, the goal (vm_committed_as), and hysteresis
 183  * parameters to set a new target balloon size
 184  */
 185 static void selfballoon_process(struct work_struct *work)
 186 {
 187         unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
 188         unsigned long useful_pages;
 189         bool reset_timer = false;
 190
 191         if (xen_selfballooning_enabled) {
 192                 cur_pages = totalram_pages;
 193                 tgt_pages = cur_pages; /* default is no change */
 194                 goal_pages = vm_memory_committed() +
 195                                 totalreserve_pages +
 196                                 MB2PAGES(selfballoon_reserved_mb);
 197 #ifdef CONFIG_FRONTSWAP
 198                 /* allow space for frontswap pages to be repatriated */
 199                 if (frontswap_selfshrinking)
 200                         goal_pages += frontswap_curr_pages();
 201 #endif
 202                 if (cur_pages > goal_pages)
 203                         tgt_pages = cur_pages -
 204                                 ((cur_pages - goal_pages) /
 205                                   selfballoon_downhysteresis);
 206                 else if (cur_pages < goal_pages)
 207                         tgt_pages = cur_pages +
 208                                 ((goal_pages - cur_pages) /
 209                                   selfballoon_uphysteresis);
 210                 /* else if cur_pages == goal_pages, no change */
 211                 useful_pages = max_pfn - totalreserve_pages;
 212                 if (selfballoon_min_usable_mb != 0)
 213                         floor_pages = totalreserve_pages +
 214                                         MB2PAGES(selfballoon_min_usable_mb);
 215                 /* piecewise linear function ending in ~3% slope */
 216                 else if (useful_pages < MB2PAGES(16))
 217                         floor_pages = max_pfn; /* not worth ballooning */
 218                 else if (useful_pages < MB2PAGES(64))
 219                         floor_pages = totalreserve_pages + MB2PAGES(16) +
 220                                         ((useful_pages - MB2PAGES(16)) >> 1);
 221                 else if (useful_pages < MB2PAGES(512))
 222                         floor_pages = totalreserve_pages + MB2PAGES(40) +
 223                                         ((useful_pages - MB2PAGES(40)) >> 3);
 224                 else /* useful_pages >= MB2PAGES(512) */
 225                         floor_pages = totalreserve_pages + MB2PAGES(99) +
 226                                         ((useful_pages - MB2PAGES(99)) >> 5);
 227                 if (tgt_pages < floor_pages)
 228                         tgt_pages = floor_pages;
 229                 balloon_set_new_target(tgt_pages +
 230                         balloon_stats.current_pages - totalram_pages);
 231                 reset_timer = true;
 232         }
 233 #ifdef CONFIG_FRONTSWAP
 234         if (frontswap_selfshrinking) {
 235                 frontswap_selfshrink();
 236                 reset_timer = true;
 237         }
 238 #endif
 239         if (reset_timer)
 240                 schedule_delayed_work(&selfballoon_worker,
 241                         selfballoon_interval * HZ);
 242 }
 243
 244 #ifdef CONFIG_SYSFS
 245
 246 #include <linux/capability.h>
 247
 248 #define SELFBALLOON_SHOW(name, format, args...)                         \
 249         static ssize_t show_##name(struct device *dev,  \
 250                                           struct device_attribute *attr, \
 251                                           char *buf) \
 252         { \
 253                 return sprintf(buf, format, ##args); \
 254         }
 255
 256 SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
 257
 258 static ssize_t store_selfballooning(struct device *dev,
 259                             struct device_attribute *attr,
 260                             const char *buf,
 261                             size_t count)
 262 {
 263         bool was_enabled = xen_selfballooning_enabled;
 264         unsigned long tmp;
 265         int err;
 266
 267         if (!capable(CAP_SYS_ADMIN))
 268                 return -EPERM;
 269
 270         err = kstrtoul(buf, 10, &tmp);
 271         if (err)
 272                 return err;
 273         if ((tmp != 0) && (tmp != 1))
 274                 return -EINVAL;
 275
 276         xen_selfballooning_enabled = !!tmp;
 277         if (!was_enabled && xen_selfballooning_enabled)
 278                 schedule_delayed_work(&selfballoon_worker,
 279                         selfballoon_interval * HZ);
 280
 281         return count;
 282 }
 283
 284 static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
 285                    show_selfballooning, store_selfballooning);
 286
 287 SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
 288
 289 static ssize_t store_selfballoon_interval(struct device *dev,
 290                                           struct device_attribute *attr,
 291                                           const char *buf,
 292                                           size_t count)
 293 {
 294         unsigned long val;
 295         int err;
 296
 297         if (!capable(CAP_SYS_ADMIN))
 298                 return -EPERM;
 299         err = kstrtoul(buf, 10, &val);
 300         if (err)
 301                 return err;
 302         if (val == 0)
 303                 return -EINVAL;
 304         selfballoon_interval = val;
 305         return count;
 306 }
 307
 308 static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
 309                    show_selfballoon_interval, store_selfballoon_interval);
 310
 311 SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
 312
 313 static ssize_t store_selfballoon_downhys(struct device *dev,
 314                                          struct device_attribute *attr,
 315                                          const char *buf,
 316                                          size_t count)
 317 {
 318         unsigned long val;
 319         int err;
 320
 321         if (!capable(CAP_SYS_ADMIN))
 322                 return -EPERM;
 323         err = kstrtoul(buf, 10, &val);
 324         if (err)
 325                 return err;
 326         if (val == 0)
 327                 return -EINVAL;
 328         selfballoon_downhysteresis = val;
 329         return count;
 330 }
 331
 332 static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
 333                    show_selfballoon_downhys, store_selfballoon_downhys);
 334
 335
 336 SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
 337
 338 static ssize_t store_selfballoon_uphys(struct device *dev,
 339                                        struct device_attribute *attr,
 340                                        const char *buf,
 341                                        size_t count)
 342 {
 343         unsigned long val;
 344         int err;
 345
 346         if (!capable(CAP_SYS_ADMIN))
 347                 return -EPERM;
 348         err = kstrtoul(buf, 10, &val);
 349         if (err)
 350                 return err;
 351         if (val == 0)
 352                 return -EINVAL;
 353         selfballoon_uphysteresis = val;
 354         return count;
 355 }
 356
 357 static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
 358                    show_selfballoon_uphys, store_selfballoon_uphys);
 359
 360 SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
 361                                 selfballoon_min_usable_mb);
 362
 363 static ssize_t store_selfballoon_min_usable_mb(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 = kstrtoul(buf, 10, &val);
 374         if (err)
 375                 return err;
 376         if (val == 0)
 377                 return -EINVAL;
 378         selfballoon_min_usable_mb = val;
 379         return count;
 380 }
 381
 382 static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
 383                    show_selfballoon_min_usable_mb,
 384                    store_selfballoon_min_usable_mb);
 385
 386 SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
 387                                 selfballoon_reserved_mb);
 388
 389 static ssize_t store_selfballoon_reserved_mb(struct device *dev,
 390                                              struct device_attribute *attr,
 391                                              const char *buf,
 392                                              size_t count)
 393 {
 394         unsigned long val;
 395         int err;
 396
 397         if (!capable(CAP_SYS_ADMIN))
 398                 return -EPERM;
 399         err = kstrtoul(buf, 10, &val);
 400         if (err)
 401                 return err;
 402         if (val == 0)
 403                 return -EINVAL;
 404         selfballoon_reserved_mb = val;
 405         return count;
 406 }
 407
 408 static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
 409                    show_selfballoon_reserved_mb,
 410                    store_selfballoon_reserved_mb);
 411
 412
 413 #ifdef CONFIG_FRONTSWAP
 414 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
 415
 416 static ssize_t store_frontswap_selfshrinking(struct device *dev,
 417                                              struct device_attribute *attr,
 418                                              const char *buf,
 419                                              size_t count)
 420 {
 421         bool was_enabled = frontswap_selfshrinking;
 422         unsigned long tmp;
 423         int err;
 424
 425         if (!capable(CAP_SYS_ADMIN))
 426                 return -EPERM;
 427         err = kstrtoul(buf, 10, &tmp);
 428         if (err)
 429                 return err;
 430         if ((tmp != 0) && (tmp != 1))
 431                 return -EINVAL;
 432         frontswap_selfshrinking = !!tmp;
 433         if (!was_enabled && !xen_selfballooning_enabled &&
 434              frontswap_selfshrinking)
 435                 schedule_delayed_work(&selfballoon_worker,
 436                         selfballoon_interval * HZ);
 437
 438         return count;
 439 }
 440
 441 static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
 442                    show_frontswap_selfshrinking, store_frontswap_selfshrinking);
 443
 444 SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
 445
 446 static ssize_t store_frontswap_inertia(struct device *dev,
 447                                        struct device_attribute *attr,
 448                                        const char *buf,
 449                                        size_t count)
 450 {
 451         unsigned long val;
 452         int err;
 453
 454         if (!capable(CAP_SYS_ADMIN))
 455                 return -EPERM;
 456         err = kstrtoul(buf, 10, &val);
 457         if (err)
 458                 return err;
 459         if (val == 0)
 460                 return -EINVAL;
 461         frontswap_inertia = val;
 462         frontswap_inertia_counter = val;
 463         return count;
 464 }
 465
 466 static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
 467                    show_frontswap_inertia, store_frontswap_inertia);
 468
 469 SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
 470
 471 static ssize_t store_frontswap_hysteresis(struct device *dev,
 472                                           struct device_attribute *attr,
 473                                           const char *buf,
 474                                           size_t count)
 475 {
 476         unsigned long val;
 477         int err;
 478
 479         if (!capable(CAP_SYS_ADMIN))
 480                 return -EPERM;
 481         err = kstrtoul(buf, 10, &val);
 482         if (err)
 483                 return err;
 484         if (val == 0)
 485                 return -EINVAL;
 486         frontswap_hysteresis = val;
 487         return count;
 488 }
 489
 490 static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
 491                    show_frontswap_hysteresis, store_frontswap_hysteresis);
 492
 493 #endif /* CONFIG_FRONTSWAP */
 494
 495 static struct attribute *selfballoon_attrs[] = {
 496         &dev_attr_selfballooning.attr,
 497         &dev_attr_selfballoon_interval.attr,
 498         &dev_attr_selfballoon_downhysteresis.attr,
 499         &dev_attr_selfballoon_uphysteresis.attr,
 500         &dev_attr_selfballoon_min_usable_mb.attr,
 501         &dev_attr_selfballoon_reserved_mb.attr,
 502 #ifdef CONFIG_FRONTSWAP
 503         &dev_attr_frontswap_selfshrinking.attr,
 504         &dev_attr_frontswap_hysteresis.attr,
 505         &dev_attr_frontswap_inertia.attr,
 506 #endif
 507         NULL
 508 };
 509
 510 static const struct attribute_group selfballoon_group = {
 511         .name = "selfballoon",
 512         .attrs = selfballoon_attrs
 513 };
 514 #endif
 515
 516 int register_xen_selfballooning(struct device *dev)
 517 {
 518         int error = -1;
 519
 520 #ifdef CONFIG_SYSFS
 521         error = sysfs_create_group(&dev->kobj, &selfballoon_group);
 522 #endif
 523         return error;
 524 }
 525 EXPORT_SYMBOL(register_xen_selfballooning);
 526
 527 int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
 528 {
 529         bool enable = false;
 530         unsigned long reserve_pages;
 531
 532         if (!xen_domain())
 533                 return -ENODEV;
 534
 535         if (xen_initial_domain()) {
 536                 pr_info("Xen selfballooning driver disabled for domain0\n");
 537                 return -ENODEV;
 538         }
 539
 540         xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
 541         if (xen_selfballooning_enabled) {
 542                 pr_info("Initializing Xen selfballooning driver\n");
 543                 enable = true;
 544         }
 545 #ifdef CONFIG_FRONTSWAP
 546         frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
 547         if (frontswap_selfshrinking) {
 548                 pr_info("Initializing frontswap selfshrinking driver\n");
 549                 enable = true;
 550         }
 551 #endif
 552         if (!enable)
 553                 return -ENODEV;
 554
 555         /*
 556          * Give selfballoon_reserved_mb a default value(10% of total ram pages)
 557          * to make selfballoon not so aggressive.
 558          *
 559          * There are mainly two reasons:
 560          * 1) The original goal_page didn't consider some pages used by kernel
 561          *    space, like slab pages and memory used by device drivers.
 562          *
 563          * 2) The balloon driver may not give back memory to guest OS fast
 564          *    enough when the workload suddenly aquries a lot of physical memory.
 565          *
 566          * In both cases, the guest OS will suffer from memory pressure and
 567          * OOM killer may be triggered.
 568          * By reserving extra 10% of total ram pages, we can keep the system
 569          * much more reliably and response faster in some cases.
 570          */
 571         if (!selfballoon_reserved_mb) {
 572                 reserve_pages = totalram_pages / 10;
 573                 selfballoon_reserved_mb = PAGES2MB(reserve_pages);
 574         }
 575         schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
 576
 577         return 0;
 578 }
 579 EXPORT_SYMBOL(xen_selfballoon_init);