drivers/xen/balloon.c

   1 /******************************************************************************
   2  * Xen balloon driver - enables returning/claiming memory to/from Xen.
   3  *
   4  * Copyright (c) 2003, B Dragovic
   5  * Copyright (c) 2003-2004, M Williamson, K Fraser
   6  * Copyright (c) 2005 Dan M. Smith, IBM Corporation
   7  * Copyright (c) 2010 Daniel Kiper
   8  *
   9  * Memory hotplug support was written by Daniel Kiper. Work on
  10  * it was sponsored by Google under Google Summer of Code 2010
  11  * program. Jeremy Fitzhardinge from Citrix was the mentor for
  12  * this project.
  13  *
  14  * This program is free software; you can redistribute it and/or
  15  * modify it under the terms of the GNU General Public License version 2
  16  * as published by the Free Software Foundation; or, when distributed
  17  * separately from the Linux kernel or incorporated into other
  18  * software packages, subject to the following license:
  19  *
  20  * Permission is hereby granted, free of charge, to any person obtaining a copy
  21  * of this source file (the "Software"), to deal in the Software without
  22  * restriction, including without limitation the rights to use, copy, modify,
  23  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
  24  * and to permit persons to whom the Software is furnished to do so, subject to
  25  * the following conditions:
  26  *
  27  * The above copyright notice and this permission notice shall be included in
  28  * all copies or substantial portions of the Software.
  29  *
  30  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  31  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  32  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  33  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  34  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  35  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  36  * IN THE SOFTWARE.
  37  */
  38
  39 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
  40
  41 #include <linux/cpu.h>
  42 #include <linux/kernel.h>
  43 #include <linux/sched.h>
  44 #include <linux/cred.h>
  45 #include <linux/errno.h>
  46 #include <linux/mm.h>
  47 #include <linux/bootmem.h>
  48 #include <linux/pagemap.h>
  49 #include <linux/highmem.h>
  50 #include <linux/mutex.h>
  51 #include <linux/list.h>
  52 #include <linux/gfp.h>
  53 #include <linux/notifier.h>
  54 #include <linux/memory.h>
  55 #include <linux/memory_hotplug.h>
  56 #include <linux/percpu-defs.h>
  57 #include <linux/slab.h>
  58 #include <linux/sysctl.h>
  59
  60 #include <asm/page.h>
  61 #include <asm/pgalloc.h>
  62 #include <asm/pgtable.h>
  63 #include <asm/tlb.h>
  64
  65 #include <asm/xen/hypervisor.h>
  66 #include <asm/xen/hypercall.h>
  67
  68 #include <xen/xen.h>
  69 #include <xen/interface/xen.h>
  70 #include <xen/interface/memory.h>
  71 #include <xen/balloon.h>
  72 #include <xen/features.h>
  73 #include <xen/page.h>
  74 #include <xen/mem-reservation.h>
  75
  76 static int xen_hotplug_unpopulated;
  77
  78 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
  79
  80 static int zero;
  81 static int one = 1;
  82
  83 static struct ctl_table balloon_table[] = {
  84         {
  85                 .procname       = "hotplug_unpopulated",
  86                 .data           = &xen_hotplug_unpopulated,
  87                 .maxlen         = sizeof(int),
  88                 .mode           = 0644,
  89                 .proc_handler   = proc_dointvec_minmax,
  90                 .extra1         = &zero,
  91                 .extra2         = &one,
  92         },
  93         { }
  94 };
  95
  96 static struct ctl_table balloon_root[] = {
  97         {
  98                 .procname       = "balloon",
  99                 .mode           = 0555,
 100                 .child          = balloon_table,
 101         },
 102         { }
 103 };
 104
 105 static struct ctl_table xen_root[] = {
 106         {
 107                 .procname       = "xen",
 108                 .mode           = 0555,
 109                 .child          = balloon_root,
 110         },
 111         { }
 112 };
 113
 114 #endif
 115
 116 /*
 117  * Use one extent per PAGE_SIZE to avoid to break down the page into
 118  * multiple frame.
 119  */
 120 #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
 121
 122 /*
 123  * balloon_process() state:
 124  *
 125  * BP_DONE: done or nothing to do,
 126  * BP_WAIT: wait to be rescheduled,
 127  * BP_EAGAIN: error, go to sleep,
 128  * BP_ECANCELED: error, balloon operation canceled.
 129  */
 130
 131 enum bp_state {
 132         BP_DONE,
 133         BP_WAIT,
 134         BP_EAGAIN,
 135         BP_ECANCELED
 136 };
 137
 138
 139 static DEFINE_MUTEX(balloon_mutex);
 140
 141 struct balloon_stats balloon_stats;
 142 EXPORT_SYMBOL_GPL(balloon_stats);
 143
 144 /* We increase/decrease in batches which fit in a page */
 145 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
 146
 147
 148 /* List of ballooned pages, threaded through the mem_map array. */
 149 static LIST_HEAD(ballooned_pages);
 150 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
 151
 152 /* Main work function, always executed in process context. */
 153 static void balloon_process(struct work_struct *work);
 154 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
 155
 156 /* When ballooning out (allocating memory to return to Xen) we don't really
 157    want the kernel to try too hard since that can trigger the oom killer. */
 158 #define GFP_BALLOON \
 159         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 160
 161 /* balloon_append: add the given page to the balloon. */
 162 static void __balloon_append(struct page *page)
 163 {
 164         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 165         if (PageHighMem(page)) {
 166                 list_add_tail(&page->lru, &ballooned_pages);
 167                 balloon_stats.balloon_high++;
 168         } else {
 169                 list_add(&page->lru, &ballooned_pages);
 170                 balloon_stats.balloon_low++;
 171         }
 172         wake_up(&balloon_wq);
 173 }
 174
 175 static void balloon_append(struct page *page)
 176 {
 177         __balloon_append(page);
 178 }
 179
 180 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 181 static struct page *balloon_retrieve(bool require_lowmem)
 182 {
 183         struct page *page;
 184
 185         if (list_empty(&ballooned_pages))
 186                 return NULL;
 187
 188         page = list_entry(ballooned_pages.next, struct page, lru);
 189         if (require_lowmem && PageHighMem(page))
 190                 return NULL;
 191         list_del(&page->lru);
 192
 193         if (PageHighMem(page))
 194                 balloon_stats.balloon_high--;
 195         else
 196                 balloon_stats.balloon_low--;
 197
 198         return page;
 199 }
 200
 201 static struct page *balloon_next_page(struct page *page)
 202 {
 203         struct list_head *next = page->lru.next;
 204         if (next == &ballooned_pages)
 205                 return NULL;
 206         return list_entry(next, struct page, lru);
 207 }
 208
 209 static enum bp_state update_schedule(enum bp_state state)
 210 {
 211         if (state == BP_WAIT)
 212                 return BP_WAIT;
 213
 214         if (state == BP_ECANCELED)
 215                 return BP_ECANCELED;
 216
 217         if (state == BP_DONE) {
 218                 balloon_stats.schedule_delay = 1;
 219                 balloon_stats.retry_count = 1;
 220                 return BP_DONE;
 221         }
 222
 223         ++balloon_stats.retry_count;
 224
 225         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
 226                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
 227                 balloon_stats.schedule_delay = 1;
 228                 balloon_stats.retry_count = 1;
 229                 return BP_ECANCELED;
 230         }
 231
 232         balloon_stats.schedule_delay <<= 1;
 233
 234         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
 235                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
 236
 237         return BP_EAGAIN;
 238 }
 239
 240 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 241 static void release_memory_resource(struct resource *resource)
 242 {
 243         if (!resource)
 244                 return;
 245
 246         /*
 247          * No need to reset region to identity mapped since we now
 248          * know that no I/O can be in this region
 249          */
 250         release_resource(resource);
 251         kfree(resource);
 252 }
 253
 254 static struct resource *additional_memory_resource(phys_addr_t size)
 255 {
 256         struct resource *res;
 257         int ret;
 258
 259         res = kzalloc(sizeof(*res), GFP_KERNEL);
 260         if (!res)
 261                 return NULL;
 262
 263         res->name = "System RAM";
 264         res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
 265
 266         ret = allocate_resource(&iomem_resource, res,
 267                                 size, 0, -1,
 268                                 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
 269         if (ret < 0) {
 270                 pr_err("Cannot allocate new System RAM resource\n");
 271                 kfree(res);
 272                 return NULL;
 273         }
 274
 275 #ifdef CONFIG_SPARSEMEM
 276         {
 277                 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
 278                 unsigned long pfn = res->start >> PAGE_SHIFT;
 279
 280                 if (pfn > limit) {
 281                         pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n",
 282                                pfn, limit);
 283                         release_memory_resource(res);
 284                         return NULL;
 285                 }
 286         }
 287 #endif
 288
 289         return res;
 290 }
 291
 292 static enum bp_state reserve_additional_memory(void)
 293 {
 294         long credit;
 295         struct resource *resource;
 296         int nid, rc;
 297         unsigned long balloon_hotplug;
 298
 299         credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
 300                 - balloon_stats.total_pages;
 301
 302         /*
 303          * Already hotplugged enough pages?  Wait for them to be
 304          * onlined.
 305          */
 306         if (credit <= 0)
 307                 return BP_WAIT;
 308
 309         balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
 310
 311         resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
 312         if (!resource)
 313                 goto err;
 314
 315         nid = memory_add_physaddr_to_nid(resource->start);
 316
 317 #ifdef CONFIG_XEN_HAVE_PVMMU
 318         /*
 319          * We don't support PV MMU when Linux and Xen is using
 320          * different page granularity.
 321          */
 322         BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
 323
 324         /*
 325          * add_memory() will build page tables for the new memory so
 326          * the p2m must contain invalid entries so the correct
 327          * non-present PTEs will be written.
 328          *
 329          * If a failure occurs, the original (identity) p2m entries
 330          * are not restored since this region is now known not to
 331          * conflict with any devices.
 332          */
 333         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 334                 unsigned long pfn, i;
 335
 336                 pfn = PFN_DOWN(resource->start);
 337                 for (i = 0; i < balloon_hotplug; i++) {
 338                         if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
 339                                 pr_warn("set_phys_to_machine() failed, no memory added\n");
 340                                 goto err;
 341                         }
 342                 }
 343         }
 344 #endif
 345
 346         /*
 347          * add_memory_resource() will call online_pages() which in its turn
 348          * will call xen_online_page() callback causing deadlock if we don't
 349          * release balloon_mutex here. Unlocking here is safe because the
 350          * callers drop the mutex before trying again.
 351          */
 352         mutex_unlock(&balloon_mutex);
 353         /* add_memory_resource() requires the device_hotplug lock */
 354         lock_device_hotplug();
 355         rc = add_memory_resource(nid, resource, memhp_auto_online);
 356         unlock_device_hotplug();
 357         mutex_lock(&balloon_mutex);
 358
 359         if (rc) {
 360                 pr_warn("Cannot add additional memory (%i)\n", rc);
 361                 goto err;
 362         }
 363
 364         balloon_stats.total_pages += balloon_hotplug;
 365
 366         return BP_WAIT;
 367   err:
 368         release_memory_resource(resource);
 369         return BP_ECANCELED;
 370 }
 371
 372 static void xen_online_page(struct page *page)
 373 {
 374         __online_page_set_limits(page);
 375
 376         mutex_lock(&balloon_mutex);
 377
 378         __balloon_append(page);
 379
 380         mutex_unlock(&balloon_mutex);
 381 }
 382
 383 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 384 {
 385         if (val == MEM_ONLINE)
 386                 schedule_delayed_work(&balloon_worker, 0);
 387
 388         return NOTIFY_OK;
 389 }
 390
 391 static struct notifier_block xen_memory_nb = {
 392         .notifier_call = xen_memory_notifier,
 393         .priority = 0
 394 };
 395 #else
 396 static enum bp_state reserve_additional_memory(void)
 397 {
 398         balloon_stats.target_pages = balloon_stats.current_pages +
 399                                      balloon_stats.target_unpopulated;
 400         return BP_ECANCELED;
 401 }
 402 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 403
 404 static long current_credit(void)
 405 {
 406         return balloon_stats.target_pages - balloon_stats.current_pages;
 407 }
 408
 409 static bool balloon_is_inflated(void)
 410 {
 411         return balloon_stats.balloon_low || balloon_stats.balloon_high;
 412 }
 413
 414 static enum bp_state increase_reservation(unsigned long nr_pages)
 415 {
 416         int rc;
 417         unsigned long i;
 418         struct page   *page;
 419
 420         if (nr_pages > ARRAY_SIZE(frame_list))
 421                 nr_pages = ARRAY_SIZE(frame_list);
 422
 423         page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
 424         for (i = 0; i < nr_pages; i++) {
 425                 if (!page) {
 426                         nr_pages = i;
 427                         break;
 428                 }
 429
 430                 frame_list[i] = page_to_xen_pfn(page);
 431                 page = balloon_next_page(page);
 432         }
 433
 434         rc = xenmem_reservation_increase(nr_pages, frame_list);
 435         if (rc <= 0)
 436                 return BP_EAGAIN;
 437
 438         for (i = 0; i < rc; i++) {
 439                 page = balloon_retrieve(false);
 440                 BUG_ON(page == NULL);
 441
 442                 xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
 443
 444                 /* Relinquish the page back to the allocator. */
 445                 free_reserved_page(page);
 446         }
 447
 448         balloon_stats.current_pages += rc;
 449
 450         return BP_DONE;
 451 }
 452
 453 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 454 {
 455         enum bp_state state = BP_DONE;
 456         unsigned long i;
 457         struct page *page, *tmp;
 458         int ret;
 459         LIST_HEAD(pages);
 460
 461         if (nr_pages > ARRAY_SIZE(frame_list))
 462                 nr_pages = ARRAY_SIZE(frame_list);
 463
 464         for (i = 0; i < nr_pages; i++) {
 465                 page = alloc_page(gfp);
 466                 if (page == NULL) {
 467                         nr_pages = i;
 468                         state = BP_EAGAIN;
 469                         break;
 470                 }
 471                 adjust_managed_page_count(page, -1);
 472                 xenmem_reservation_scrub_page(page);
 473                 list_add(&page->lru, &pages);
 474         }
 475
 476         /*
 477          * Ensure that ballooned highmem pages don't have kmaps.
 478          *
 479          * Do this before changing the p2m as kmap_flush_unused()
 480          * reads PTEs to obtain pages (and hence needs the original
 481          * p2m entry).
 482          */
 483         kmap_flush_unused();
 484
 485         /*
 486          * Setup the frame, update direct mapping, invalidate P2M,
 487          * and add to balloon.
 488          */
 489         i = 0;
 490         list_for_each_entry_safe(page, tmp, &pages, lru) {
 491                 frame_list[i++] = xen_page_to_gfn(page);
 492
 493                 xenmem_reservation_va_mapping_reset(1, &page);
 494
 495                 list_del(&page->lru);
 496
 497                 balloon_append(page);
 498         }
 499
 500         flush_tlb_all();
 501
 502         ret = xenmem_reservation_decrease(nr_pages, frame_list);
 503         BUG_ON(ret != nr_pages);
 504
 505         balloon_stats.current_pages -= nr_pages;
 506
 507         return state;
 508 }
 509
 510 /*
 511  * As this is a work item it is guaranteed to run as a single instance only.
 512  * We may of course race updates of the target counts (which are protected
 513  * by the balloon lock), or with changes to the Xen hard limit, but we will
 514  * recover from these in time.
 515  */
 516 static void balloon_process(struct work_struct *work)
 517 {
 518         enum bp_state state = BP_DONE;
 519         long credit;
 520
 521
 522         do {
 523                 mutex_lock(&balloon_mutex);
 524
 525                 credit = current_credit();
 526
 527                 if (credit > 0) {
 528                         if (balloon_is_inflated())
 529                                 state = increase_reservation(credit);
 530                         else
 531                                 state = reserve_additional_memory();
 532                 }
 533
 534                 if (credit < 0) {
 535                         long n_pages;
 536
 537                         n_pages = min(-credit, si_mem_available());
 538                         state = decrease_reservation(n_pages, GFP_BALLOON);
 539                         if (state == BP_DONE && n_pages != -credit &&
 540                             n_pages < totalreserve_pages)
 541                                 state = BP_EAGAIN;
 542                 }
 543
 544                 state = update_schedule(state);
 545
 546                 mutex_unlock(&balloon_mutex);
 547
 548                 cond_resched();
 549
 550         } while (credit && state == BP_DONE);
 551
 552         /* Schedule more work if there is some still to be done. */
 553         if (state == BP_EAGAIN)
 554                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 555 }
 556
 557 /* Resets the Xen limit, sets new target, and kicks off processing. */
 558 void balloon_set_new_target(unsigned long target)
 559 {
 560         /* No need for lock. Not read-modify-write updates. */
 561         balloon_stats.target_pages = target;
 562         schedule_delayed_work(&balloon_worker, 0);
 563 }
 564 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 565
 566 static int add_ballooned_pages(int nr_pages)
 567 {
 568         enum bp_state st;
 569
 570         if (xen_hotplug_unpopulated) {
 571                 st = reserve_additional_memory();
 572                 if (st != BP_ECANCELED) {
 573                         mutex_unlock(&balloon_mutex);
 574                         wait_event(balloon_wq,
 575                                    !list_empty(&ballooned_pages));
 576                         mutex_lock(&balloon_mutex);
 577                         return 0;
 578                 }
 579         }
 580
 581         if (si_mem_available() < nr_pages)
 582                 return -ENOMEM;
 583
 584         st = decrease_reservation(nr_pages, GFP_USER);
 585         if (st != BP_DONE)
 586                 return -ENOMEM;
 587
 588         return 0;
 589 }
 590
 591 /**
 592  * alloc_xenballooned_pages - get pages that have been ballooned out
 593  * @nr_pages: Number of pages to get
 594  * @pages: pages returned
 595  * @return 0 on success, error otherwise
 596  */
 597 int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 598 {
 599         int pgno = 0;
 600         struct page *page;
 601         int ret;
 602
 603         mutex_lock(&balloon_mutex);
 604
 605         balloon_stats.target_unpopulated += nr_pages;
 606
 607         while (pgno < nr_pages) {
 608                 page = balloon_retrieve(true);
 609                 if (page) {
 610                         pages[pgno++] = page;
 611 #ifdef CONFIG_XEN_HAVE_PVMMU
 612                         /*
 613                          * We don't support PV MMU when Linux and Xen is using
 614                          * different page granularity.
 615                          */
 616                         BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
 617
 618                         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 619                                 ret = xen_alloc_p2m_entry(page_to_pfn(page));
 620                                 if (ret < 0)
 621                                         goto out_undo;
 622                         }
 623 #endif
 624                 } else {
 625                         ret = add_ballooned_pages(nr_pages - pgno);
 626                         if (ret < 0)
 627                                 goto out_undo;
 628                 }
 629         }
 630         mutex_unlock(&balloon_mutex);
 631         return 0;
 632  out_undo:
 633         mutex_unlock(&balloon_mutex);
 634         free_xenballooned_pages(pgno, pages);
 635         return ret;
 636 }
 637 EXPORT_SYMBOL(alloc_xenballooned_pages);
 638
 639 /**
 640  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
 641  * @nr_pages: Number of pages
 642  * @pages: pages to return
 643  */
 644 void free_xenballooned_pages(int nr_pages, struct page **pages)
 645 {
 646         int i;
 647
 648         mutex_lock(&balloon_mutex);
 649
 650         for (i = 0; i < nr_pages; i++) {
 651                 if (pages[i])
 652                         balloon_append(pages[i]);
 653         }
 654
 655         balloon_stats.target_unpopulated -= nr_pages;
 656
 657         /* The balloon may be too large now. Shrink it if needed. */
 658         if (current_credit())
 659                 schedule_delayed_work(&balloon_worker, 0);
 660
 661         mutex_unlock(&balloon_mutex);
 662 }
 663 EXPORT_SYMBOL(free_xenballooned_pages);
 664
 665 #ifdef CONFIG_XEN_PV
 666 static void __init balloon_add_region(unsigned long start_pfn,
 667                                       unsigned long pages)
 668 {
 669         unsigned long pfn, extra_pfn_end;
 670         struct page *page;
 671
 672         /*
 673          * If the amount of usable memory has been limited (e.g., with
 674          * the 'mem' command line parameter), don't add pages beyond
 675          * this limit.
 676          */
 677         extra_pfn_end = min(max_pfn, start_pfn + pages);
 678
 679         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
 680                 page = pfn_to_page(pfn);
 681                 /* totalram_pages and totalhigh_pages do not
 682                    include the boot-time balloon extension, so
 683                    don't subtract from it. */
 684                 __balloon_append(page);
 685         }
 686
 687         balloon_stats.total_pages += extra_pfn_end - start_pfn;
 688 }
 689 #endif
 690
 691 static int __init balloon_init(void)
 692 {
 693         if (!xen_domain())
 694                 return -ENODEV;
 695
 696         pr_info("Initialising balloon driver\n");
 697
 698 #ifdef CONFIG_XEN_PV
 699         balloon_stats.current_pages = xen_pv_domain()
 700                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
 701                 : get_num_physpages();
 702 #else
 703         balloon_stats.current_pages = get_num_physpages();
 704 #endif
 705         balloon_stats.target_pages  = balloon_stats.current_pages;
 706         balloon_stats.balloon_low   = 0;
 707         balloon_stats.balloon_high  = 0;
 708         balloon_stats.total_pages   = balloon_stats.current_pages;
 709
 710         balloon_stats.schedule_delay = 1;
 711         balloon_stats.max_schedule_delay = 32;
 712         balloon_stats.retry_count = 1;
 713         balloon_stats.max_retry_count = 4;
 714
 715 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 716         set_online_page_callback(&xen_online_page);
 717         register_memory_notifier(&xen_memory_nb);
 718         register_sysctl_table(xen_root);
 719 #endif
 720
 721 #ifdef CONFIG_XEN_PV
 722         {
 723                 int i;
 724
 725                 /*
 726                  * Initialize the balloon with pages from the extra memory
 727                  * regions (see arch/x86/xen/setup.c).
 728                  */
 729                 for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
 730                         if (xen_extra_mem[i].n_pfns)
 731                                 balloon_add_region(xen_extra_mem[i].start_pfn,
 732                                                    xen_extra_mem[i].n_pfns);
 733         }
 734 #endif
 735
 736         /* Init the xen-balloon driver. */
 737         xen_balloon_init();
 738
 739         return 0;
 740 }
 741 subsys_initcall(balloon_init);