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/errno.h>
  45 #include <linux/module.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
  58 #include <asm/page.h>
  59 #include <asm/pgalloc.h>
  60 #include <asm/pgtable.h>
  61 #include <asm/tlb.h>
  62
  63 #include <asm/xen/hypervisor.h>
  64 #include <asm/xen/hypercall.h>
  65
  66 #include <xen/xen.h>
  67 #include <xen/interface/xen.h>
  68 #include <xen/interface/memory.h>
  69 #include <xen/balloon.h>
  70 #include <xen/features.h>
  71 #include <xen/page.h>
  72
  73 /*
  74  * balloon_process() state:
  75  *
  76  * BP_DONE: done or nothing to do,
  77  * BP_EAGAIN: error, go to sleep,
  78  * BP_ECANCELED: error, balloon operation canceled.
  79  */
  80
  81 enum bp_state {
  82         BP_DONE,
  83         BP_EAGAIN,
  84         BP_ECANCELED
  85 };
  86
  87
  88 static DEFINE_MUTEX(balloon_mutex);
  89
  90 struct balloon_stats balloon_stats;
  91 EXPORT_SYMBOL_GPL(balloon_stats);
  92
  93 /* We increase/decrease in batches which fit in a page */
  94 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(unsigned long)];
  95 static DEFINE_PER_CPU(struct page *, balloon_scratch_page);
  96
  97
  98 /* List of ballooned pages, threaded through the mem_map array. */
  99 static LIST_HEAD(ballooned_pages);
 100
 101 /* Main work function, always executed in process context. */
 102 static void balloon_process(struct work_struct *work);
 103 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
 104
 105 /* When ballooning out (allocating memory to return to Xen) we don't really
 106    want the kernel to try too hard since that can trigger the oom killer. */
 107 #define GFP_BALLOON \
 108         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 109
 110 static void scrub_page(struct page *page)
 111 {
 112 #ifdef CONFIG_XEN_SCRUB_PAGES
 113         clear_highpage(page);
 114 #endif
 115 }
 116
 117 /* balloon_append: add the given page to the balloon. */
 118 static void __balloon_append(struct page *page)
 119 {
 120         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 121         if (PageHighMem(page)) {
 122                 list_add_tail(&page->lru, &ballooned_pages);
 123                 balloon_stats.balloon_high++;
 124         } else {
 125                 list_add(&page->lru, &ballooned_pages);
 126                 balloon_stats.balloon_low++;
 127         }
 128 }
 129
 130 static void balloon_append(struct page *page)
 131 {
 132         __balloon_append(page);
 133         adjust_managed_page_count(page, -1);
 134 }
 135
 136 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 137 static struct page *balloon_retrieve(bool prefer_highmem)
 138 {
 139         struct page *page;
 140
 141         if (list_empty(&ballooned_pages))
 142                 return NULL;
 143
 144         if (prefer_highmem)
 145                 page = list_entry(ballooned_pages.prev, struct page, lru);
 146         else
 147                 page = list_entry(ballooned_pages.next, struct page, lru);
 148         list_del(&page->lru);
 149
 150         if (PageHighMem(page))
 151                 balloon_stats.balloon_high--;
 152         else
 153                 balloon_stats.balloon_low--;
 154
 155         adjust_managed_page_count(page, 1);
 156
 157         return page;
 158 }
 159
 160 static struct page *balloon_first_page(void)
 161 {
 162         if (list_empty(&ballooned_pages))
 163                 return NULL;
 164         return list_entry(ballooned_pages.next, struct page, lru);
 165 }
 166
 167 static struct page *balloon_next_page(struct page *page)
 168 {
 169         struct list_head *next = page->lru.next;
 170         if (next == &ballooned_pages)
 171                 return NULL;
 172         return list_entry(next, struct page, lru);
 173 }
 174
 175 static enum bp_state update_schedule(enum bp_state state)
 176 {
 177         if (state == BP_DONE) {
 178                 balloon_stats.schedule_delay = 1;
 179                 balloon_stats.retry_count = 1;
 180                 return BP_DONE;
 181         }
 182
 183         ++balloon_stats.retry_count;
 184
 185         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
 186                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
 187                 balloon_stats.schedule_delay = 1;
 188                 balloon_stats.retry_count = 1;
 189                 return BP_ECANCELED;
 190         }
 191
 192         balloon_stats.schedule_delay <<= 1;
 193
 194         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
 195                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
 196
 197         return BP_EAGAIN;
 198 }
 199
 200 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 201 static long current_credit(void)
 202 {
 203         return balloon_stats.target_pages - balloon_stats.current_pages -
 204                 balloon_stats.hotplug_pages;
 205 }
 206
 207 static bool balloon_is_inflated(void)
 208 {
 209         if (balloon_stats.balloon_low || balloon_stats.balloon_high ||
 210                         balloon_stats.balloon_hotplug)
 211                 return true;
 212         else
 213                 return false;
 214 }
 215
 216 /*
 217  * reserve_additional_memory() adds memory region of size >= credit above
 218  * max_pfn. New region is section aligned and size is modified to be multiple
 219  * of section size. Those features allow optimal use of address space and
 220  * establish proper alignment when this function is called first time after
 221  * boot (last section not fully populated at boot time contains unused memory
 222  * pages with PG_reserved bit not set; online_pages_range() does not allow page
 223  * onlining in whole range if first onlined page does not have PG_reserved
 224  * bit set). Real size of added memory is established at page onlining stage.
 225  */
 226
 227 static enum bp_state reserve_additional_memory(long credit)
 228 {
 229         int nid, rc;
 230         u64 hotplug_start_paddr;
 231         unsigned long balloon_hotplug = credit;
 232
 233         hotplug_start_paddr = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
 234         balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
 235         nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
 236
 237         rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);
 238
 239         if (rc) {
 240                 pr_info("%s: add_memory() failed: %i\n", __func__, rc);
 241                 return BP_EAGAIN;
 242         }
 243
 244         balloon_hotplug -= credit;
 245
 246         balloon_stats.hotplug_pages += credit;
 247         balloon_stats.balloon_hotplug = balloon_hotplug;
 248
 249         return BP_DONE;
 250 }
 251
 252 static void xen_online_page(struct page *page)
 253 {
 254         __online_page_set_limits(page);
 255
 256         mutex_lock(&balloon_mutex);
 257
 258         __balloon_append(page);
 259
 260         if (balloon_stats.hotplug_pages)
 261                 --balloon_stats.hotplug_pages;
 262         else
 263                 --balloon_stats.balloon_hotplug;
 264
 265         mutex_unlock(&balloon_mutex);
 266 }
 267
 268 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 269 {
 270         if (val == MEM_ONLINE)
 271                 schedule_delayed_work(&balloon_worker, 0);
 272
 273         return NOTIFY_OK;
 274 }
 275
 276 static struct notifier_block xen_memory_nb = {
 277         .notifier_call = xen_memory_notifier,
 278         .priority = 0
 279 };
 280 #else
 281 static long current_credit(void)
 282 {
 283         unsigned long target = balloon_stats.target_pages;
 284
 285         target = min(target,
 286                      balloon_stats.current_pages +
 287                      balloon_stats.balloon_low +
 288                      balloon_stats.balloon_high);
 289
 290         return target - balloon_stats.current_pages;
 291 }
 292
 293 static bool balloon_is_inflated(void)
 294 {
 295         if (balloon_stats.balloon_low || balloon_stats.balloon_high)
 296                 return true;
 297         else
 298                 return false;
 299 }
 300
 301 static enum bp_state reserve_additional_memory(long credit)
 302 {
 303         balloon_stats.target_pages = balloon_stats.current_pages;
 304         return BP_DONE;
 305 }
 306 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 307
 308 static enum bp_state increase_reservation(unsigned long nr_pages)
 309 {
 310         int rc;
 311         unsigned long  pfn, i;
 312         struct page   *page;
 313         struct xen_memory_reservation reservation = {
 314                 .address_bits = 0,
 315                 .extent_order = 0,
 316                 .domid        = DOMID_SELF
 317         };
 318
 319 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 320         if (!balloon_stats.balloon_low && !balloon_stats.balloon_high) {
 321                 nr_pages = min(nr_pages, balloon_stats.balloon_hotplug);
 322                 balloon_stats.hotplug_pages += nr_pages;
 323                 balloon_stats.balloon_hotplug -= nr_pages;
 324                 return BP_DONE;
 325         }
 326 #endif
 327
 328         if (nr_pages > ARRAY_SIZE(frame_list))
 329                 nr_pages = ARRAY_SIZE(frame_list);
 330
 331         page = balloon_first_page();
 332         for (i = 0; i < nr_pages; i++) {
 333                 if (!page) {
 334                         nr_pages = i;
 335                         break;
 336                 }
 337                 frame_list[i] = page_to_pfn(page);
 338                 page = balloon_next_page(page);
 339         }
 340
 341         set_xen_guest_handle(reservation.extent_start, frame_list);
 342         reservation.nr_extents = nr_pages;
 343         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 344         if (rc <= 0)
 345                 return BP_EAGAIN;
 346
 347         for (i = 0; i < rc; i++) {
 348                 page = balloon_retrieve(false);
 349                 BUG_ON(page == NULL);
 350
 351                 pfn = page_to_pfn(page);
 352
 353 #ifdef CONFIG_XEN_HAVE_PVMMU
 354                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 355                         set_phys_to_machine(pfn, frame_list[i]);
 356
 357                         /* Link back into the page tables if not highmem. */
 358                         if (!PageHighMem(page)) {
 359                                 int ret;
 360                                 ret = HYPERVISOR_update_va_mapping(
 361                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 362                                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 363                                                 0);
 364                                 BUG_ON(ret);
 365                         }
 366                 }
 367 #endif
 368
 369                 /* Relinquish the page back to the allocator. */
 370                 __free_reserved_page(page);
 371         }
 372
 373         balloon_stats.current_pages += rc;
 374
 375         return BP_DONE;
 376 }
 377
 378 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 379 {
 380         enum bp_state state = BP_DONE;
 381         unsigned long  pfn, i;
 382         struct page   *page;
 383         int ret;
 384         struct xen_memory_reservation reservation = {
 385                 .address_bits = 0,
 386                 .extent_order = 0,
 387                 .domid        = DOMID_SELF
 388         };
 389
 390 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 391         if (balloon_stats.hotplug_pages) {
 392                 nr_pages = min(nr_pages, balloon_stats.hotplug_pages);
 393                 balloon_stats.hotplug_pages -= nr_pages;
 394                 balloon_stats.balloon_hotplug += nr_pages;
 395                 return BP_DONE;
 396         }
 397 #endif
 398
 399         if (nr_pages > ARRAY_SIZE(frame_list))
 400                 nr_pages = ARRAY_SIZE(frame_list);
 401
 402         for (i = 0; i < nr_pages; i++) {
 403                 page = alloc_page(gfp);
 404                 if (page == NULL) {
 405                         nr_pages = i;
 406                         state = BP_EAGAIN;
 407                         break;
 408                 }
 409
 410                 pfn = page_to_pfn(page);
 411                 frame_list[i] = pfn_to_mfn(pfn);
 412
 413                 scrub_page(page);
 414
 415 #ifdef CONFIG_XEN_HAVE_PVMMU
 416                 /*
 417                  * Ballooned out frames are effectively replaced with
 418                  * a scratch frame.  Ensure direct mappings and the
 419                  * p2m are consistent.
 420                  */
 421                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 422                         unsigned long p;
 423                         struct page   *scratch_page = get_balloon_scratch_page();
 424
 425                         if (!PageHighMem(page)) {
 426                                 ret = HYPERVISOR_update_va_mapping(
 427                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 428                                                 pfn_pte(page_to_pfn(scratch_page),
 429                                                         PAGE_KERNEL_RO), 0);
 430                                 BUG_ON(ret);
 431                         }
 432                         p = page_to_pfn(scratch_page);
 433                         __set_phys_to_machine(pfn, pfn_to_mfn(p));
 434
 435                         put_balloon_scratch_page();
 436                 }
 437 #endif
 438
 439                 balloon_append(pfn_to_page(pfn));
 440         }
 441
 442         /* Ensure that ballooned highmem pages don't have kmaps. */
 443         kmap_flush_unused();
 444         flush_tlb_all();
 445
 446         set_xen_guest_handle(reservation.extent_start, frame_list);
 447         reservation.nr_extents   = nr_pages;
 448         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 449         BUG_ON(ret != nr_pages);
 450
 451         balloon_stats.current_pages -= nr_pages;
 452
 453         return state;
 454 }
 455
 456 /*
 457  * We avoid multiple worker processes conflicting via the balloon mutex.
 458  * We may of course race updates of the target counts (which are protected
 459  * by the balloon lock), or with changes to the Xen hard limit, but we will
 460  * recover from these in time.
 461  */
 462 static void balloon_process(struct work_struct *work)
 463 {
 464         enum bp_state state = BP_DONE;
 465         long credit;
 466
 467         mutex_lock(&balloon_mutex);
 468
 469         do {
 470                 credit = current_credit();
 471
 472                 if (credit > 0) {
 473                         if (balloon_is_inflated())
 474                                 state = increase_reservation(credit);
 475                         else
 476                                 state = reserve_additional_memory(credit);
 477                 }
 478
 479                 if (credit < 0)
 480                         state = decrease_reservation(-credit, GFP_BALLOON);
 481
 482                 state = update_schedule(state);
 483
 484 #ifndef CONFIG_PREEMPT
 485                 if (need_resched())
 486                         schedule();
 487 #endif
 488         } while (credit && state == BP_DONE);
 489
 490         /* Schedule more work if there is some still to be done. */
 491         if (state == BP_EAGAIN)
 492                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 493
 494         mutex_unlock(&balloon_mutex);
 495 }
 496
 497 struct page *get_balloon_scratch_page(void)
 498 {
 499         struct page *ret = get_cpu_var(balloon_scratch_page);
 500         BUG_ON(ret == NULL);
 501         return ret;
 502 }
 503
 504 void put_balloon_scratch_page(void)
 505 {
 506         put_cpu_var(balloon_scratch_page);
 507 }
 508
 509 /* Resets the Xen limit, sets new target, and kicks off processing. */
 510 void balloon_set_new_target(unsigned long target)
 511 {
 512         /* No need for lock. Not read-modify-write updates. */
 513         balloon_stats.target_pages = target;
 514         schedule_delayed_work(&balloon_worker, 0);
 515 }
 516 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 517
 518 /**
 519  * alloc_xenballooned_pages - get pages that have been ballooned out
 520  * @nr_pages: Number of pages to get
 521  * @pages: pages returned
 522  * @highmem: allow highmem pages
 523  * @return 0 on success, error otherwise
 524  */
 525 int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
 526 {
 527         int pgno = 0;
 528         struct page *page;
 529         mutex_lock(&balloon_mutex);
 530         while (pgno < nr_pages) {
 531                 page = balloon_retrieve(highmem);
 532                 if (page && (highmem || !PageHighMem(page))) {
 533                         pages[pgno++] = page;
 534                 } else {
 535                         enum bp_state st;
 536                         if (page)
 537                                 balloon_append(page);
 538                         st = decrease_reservation(nr_pages - pgno,
 539                                         highmem ? GFP_HIGHUSER : GFP_USER);
 540                         if (st != BP_DONE)
 541                                 goto out_undo;
 542                 }
 543         }
 544         mutex_unlock(&balloon_mutex);
 545         return 0;
 546  out_undo:
 547         while (pgno)
 548                 balloon_append(pages[--pgno]);
 549         /* Free the memory back to the kernel soon */
 550         schedule_delayed_work(&balloon_worker, 0);
 551         mutex_unlock(&balloon_mutex);
 552         return -ENOMEM;
 553 }
 554 EXPORT_SYMBOL(alloc_xenballooned_pages);
 555
 556 /**
 557  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
 558  * @nr_pages: Number of pages
 559  * @pages: pages to return
 560  */
 561 void free_xenballooned_pages(int nr_pages, struct page **pages)
 562 {
 563         int i;
 564
 565         mutex_lock(&balloon_mutex);
 566
 567         for (i = 0; i < nr_pages; i++) {
 568                 if (pages[i])
 569                         balloon_append(pages[i]);
 570         }
 571
 572         /* The balloon may be too large now. Shrink it if needed. */
 573         if (current_credit())
 574                 schedule_delayed_work(&balloon_worker, 0);
 575
 576         mutex_unlock(&balloon_mutex);
 577 }
 578 EXPORT_SYMBOL(free_xenballooned_pages);
 579
 580 static void __init balloon_add_region(unsigned long start_pfn,
 581                                       unsigned long pages)
 582 {
 583         unsigned long pfn, extra_pfn_end;
 584         struct page *page;
 585
 586         /*
 587          * If the amount of usable memory has been limited (e.g., with
 588          * the 'mem' command line parameter), don't add pages beyond
 589          * this limit.
 590          */
 591         extra_pfn_end = min(max_pfn, start_pfn + pages);
 592
 593         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
 594                 page = pfn_to_page(pfn);
 595                 /* totalram_pages and totalhigh_pages do not
 596                    include the boot-time balloon extension, so
 597                    don't subtract from it. */
 598                 __balloon_append(page);
 599         }
 600 }
 601
 602 static int balloon_cpu_notify(struct notifier_block *self,
 603                                     unsigned long action, void *hcpu)
 604 {
 605         int cpu = (long)hcpu;
 606         switch (action) {
 607         case CPU_UP_PREPARE:
 608                 if (per_cpu(balloon_scratch_page, cpu) != NULL)
 609                         break;
 610                 per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
 611                 if (per_cpu(balloon_scratch_page, cpu) == NULL) {
 612                         pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
 613                         return NOTIFY_BAD;
 614                 }
 615                 break;
 616         default:
 617                 break;
 618         }
 619         return NOTIFY_OK;
 620 }
 621
 622 static struct notifier_block balloon_cpu_notifier = {
 623         .notifier_call  = balloon_cpu_notify,
 624 };
 625
 626 static int __init balloon_init(void)
 627 {
 628         int i, cpu;
 629
 630         if (!xen_domain())
 631                 return -ENODEV;
 632
 633         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 634                 for_each_online_cpu(cpu)
 635                 {
 636                         per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
 637                         if (per_cpu(balloon_scratch_page, cpu) == NULL) {
 638                                 pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
 639                                 return -ENOMEM;
 640                         }
 641                 }
 642                 register_cpu_notifier(&balloon_cpu_notifier);
 643         }
 644
 645         pr_info("Initialising balloon driver\n");
 646
 647         balloon_stats.current_pages = xen_pv_domain()
 648                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
 649                 : get_num_physpages();
 650         balloon_stats.target_pages  = balloon_stats.current_pages;
 651         balloon_stats.balloon_low   = 0;
 652         balloon_stats.balloon_high  = 0;
 653
 654         balloon_stats.schedule_delay = 1;
 655         balloon_stats.max_schedule_delay = 32;
 656         balloon_stats.retry_count = 1;
 657         balloon_stats.max_retry_count = RETRY_UNLIMITED;
 658
 659 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 660         balloon_stats.hotplug_pages = 0;
 661         balloon_stats.balloon_hotplug = 0;
 662
 663         set_online_page_callback(&xen_online_page);
 664         register_memory_notifier(&xen_memory_nb);
 665 #endif
 666
 667         /*
 668          * Initialize the balloon with pages from the extra memory
 669          * regions (see arch/x86/xen/setup.c).
 670          */
 671         for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
 672                 if (xen_extra_mem[i].size)
 673                         balloon_add_region(PFN_UP(xen_extra_mem[i].start),
 674                                            PFN_DOWN(xen_extra_mem[i].size));
 675
 676         return 0;
 677 }
 678
 679 subsys_initcall(balloon_init);
 680
 681 static int __init balloon_clear(void)
 682 {
 683         int cpu;
 684
 685         for_each_possible_cpu(cpu)
 686                 per_cpu(balloon_scratch_page, cpu) = NULL;
 687
 688         return 0;
 689 }
 690 early_initcall(balloon_clear);
 691
 692 MODULE_LICENSE("GPL");