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                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 353                        phys_to_machine_mapping_valid(pfn));
 354
 355                 set_phys_to_machine(pfn, frame_list[i]);
 356
 357 #ifdef CONFIG_XEN_HAVE_PVMMU
 358                 /* Link back into the page tables if not highmem. */
 359                 if (xen_pv_domain() && !PageHighMem(page)) {
 360                         int ret;
 361                         ret = HYPERVISOR_update_va_mapping(
 362                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 363                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 364                                 0);
 365                         BUG_ON(ret);
 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                 if (xen_pv_domain() && !PageHighMem(page)) {
 417                         ret = HYPERVISOR_update_va_mapping(
 418                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 419                                 pfn_pte(page_to_pfn(__get_cpu_var(balloon_scratch_page)),
 420                                         PAGE_KERNEL_RO), 0);
 421                         BUG_ON(ret);
 422                 }
 423 #endif
 424         }
 425
 426         /* Ensure that ballooned highmem pages don't have kmaps. */
 427         kmap_flush_unused();
 428         flush_tlb_all();
 429
 430         /* No more mappings: invalidate P2M and add to balloon. */
 431         for (i = 0; i < nr_pages; i++) {
 432                 pfn = mfn_to_pfn(frame_list[i]);
 433                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 434                         unsigned long p;
 435                         struct page *pg;
 436                         pg = __get_cpu_var(balloon_scratch_page);
 437                         p = page_to_pfn(pg);
 438                         __set_phys_to_machine(pfn, pfn_to_mfn(p));
 439                 }
 440                 balloon_append(pfn_to_page(pfn));
 441         }
 442
 443         set_xen_guest_handle(reservation.extent_start, frame_list);
 444         reservation.nr_extents   = nr_pages;
 445         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 446         BUG_ON(ret != nr_pages);
 447
 448         balloon_stats.current_pages -= nr_pages;
 449
 450         return state;
 451 }
 452
 453 /*
 454  * We avoid multiple worker processes conflicting via the balloon mutex.
 455  * We may of course race updates of the target counts (which are protected
 456  * by the balloon lock), or with changes to the Xen hard limit, but we will
 457  * recover from these in time.
 458  */
 459 static void balloon_process(struct work_struct *work)
 460 {
 461         enum bp_state state = BP_DONE;
 462         long credit;
 463
 464         mutex_lock(&balloon_mutex);
 465
 466         do {
 467                 credit = current_credit();
 468
 469                 if (credit > 0) {
 470                         if (balloon_is_inflated())
 471                                 state = increase_reservation(credit);
 472                         else
 473                                 state = reserve_additional_memory(credit);
 474                 }
 475
 476                 if (credit < 0)
 477                         state = decrease_reservation(-credit, GFP_BALLOON);
 478
 479                 state = update_schedule(state);
 480
 481 #ifndef CONFIG_PREEMPT
 482                 if (need_resched())
 483                         schedule();
 484 #endif
 485         } while (credit && state == BP_DONE);
 486
 487         /* Schedule more work if there is some still to be done. */
 488         if (state == BP_EAGAIN)
 489                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 490
 491         mutex_unlock(&balloon_mutex);
 492 }
 493
 494 struct page *get_balloon_scratch_page(void)
 495 {
 496         struct page *ret = get_cpu_var(balloon_scratch_page);
 497         BUG_ON(ret == NULL);
 498         return ret;
 499 }
 500
 501 void put_balloon_scratch_page(void)
 502 {
 503         put_cpu_var(balloon_scratch_page);
 504 }
 505
 506 /* Resets the Xen limit, sets new target, and kicks off processing. */
 507 void balloon_set_new_target(unsigned long target)
 508 {
 509         /* No need for lock. Not read-modify-write updates. */
 510         balloon_stats.target_pages = target;
 511         schedule_delayed_work(&balloon_worker, 0);
 512 }
 513 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 514
 515 /**
 516  * alloc_xenballooned_pages - get pages that have been ballooned out
 517  * @nr_pages: Number of pages to get
 518  * @pages: pages returned
 519  * @highmem: allow highmem pages
 520  * @return 0 on success, error otherwise
 521  */
 522 int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
 523 {
 524         int pgno = 0;
 525         struct page *page;
 526         mutex_lock(&balloon_mutex);
 527         while (pgno < nr_pages) {
 528                 page = balloon_retrieve(highmem);
 529                 if (page && (highmem || !PageHighMem(page))) {
 530                         pages[pgno++] = page;
 531                 } else {
 532                         enum bp_state st;
 533                         if (page)
 534                                 balloon_append(page);
 535                         st = decrease_reservation(nr_pages - pgno,
 536                                         highmem ? GFP_HIGHUSER : GFP_USER);
 537                         if (st != BP_DONE)
 538                                 goto out_undo;
 539                 }
 540         }
 541         mutex_unlock(&balloon_mutex);
 542         return 0;
 543  out_undo:
 544         while (pgno)
 545                 balloon_append(pages[--pgno]);
 546         /* Free the memory back to the kernel soon */
 547         schedule_delayed_work(&balloon_worker, 0);
 548         mutex_unlock(&balloon_mutex);
 549         return -ENOMEM;
 550 }
 551 EXPORT_SYMBOL(alloc_xenballooned_pages);
 552
 553 /**
 554  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
 555  * @nr_pages: Number of pages
 556  * @pages: pages to return
 557  */
 558 void free_xenballooned_pages(int nr_pages, struct page **pages)
 559 {
 560         int i;
 561
 562         mutex_lock(&balloon_mutex);
 563
 564         for (i = 0; i < nr_pages; i++) {
 565                 if (pages[i])
 566                         balloon_append(pages[i]);
 567         }
 568
 569         /* The balloon may be too large now. Shrink it if needed. */
 570         if (current_credit())
 571                 schedule_delayed_work(&balloon_worker, 0);
 572
 573         mutex_unlock(&balloon_mutex);
 574 }
 575 EXPORT_SYMBOL(free_xenballooned_pages);
 576
 577 static void __init balloon_add_region(unsigned long start_pfn,
 578                                       unsigned long pages)
 579 {
 580         unsigned long pfn, extra_pfn_end;
 581         struct page *page;
 582
 583         /*
 584          * If the amount of usable memory has been limited (e.g., with
 585          * the 'mem' command line parameter), don't add pages beyond
 586          * this limit.
 587          */
 588         extra_pfn_end = min(max_pfn, start_pfn + pages);
 589
 590         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
 591                 page = pfn_to_page(pfn);
 592                 /* totalram_pages and totalhigh_pages do not
 593                    include the boot-time balloon extension, so
 594                    don't subtract from it. */
 595                 __balloon_append(page);
 596         }
 597 }
 598
 599 static int __cpuinit balloon_cpu_notify(struct notifier_block *self,
 600                                     unsigned long action, void *hcpu)
 601 {
 602         int cpu = (long)hcpu;
 603         switch (action) {
 604         case CPU_UP_PREPARE:
 605                 if (per_cpu(balloon_scratch_page, cpu) != NULL)
 606                         break;
 607                 per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
 608                 if (per_cpu(balloon_scratch_page, cpu) == NULL) {
 609                         pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
 610                         return NOTIFY_BAD;
 611                 }
 612                 break;
 613         default:
 614                 break;
 615         }
 616         return NOTIFY_OK;
 617 }
 618
 619 static struct notifier_block balloon_cpu_notifier __cpuinitdata = {
 620         .notifier_call  = balloon_cpu_notify,
 621 };
 622
 623 static int __init balloon_init(void)
 624 {
 625         int i, cpu;
 626
 627         if (!xen_domain())
 628                 return -ENODEV;
 629
 630         for_each_online_cpu(cpu)
 631         {
 632                 per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
 633                 if (per_cpu(balloon_scratch_page, cpu) == NULL) {
 634                         pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
 635                         return -ENOMEM;
 636                 }
 637         }
 638         register_cpu_notifier(&balloon_cpu_notifier);
 639
 640         pr_info("Initialising balloon driver\n");
 641
 642         balloon_stats.current_pages = xen_pv_domain()
 643                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
 644                 : max_pfn;
 645         balloon_stats.target_pages  = balloon_stats.current_pages;
 646         balloon_stats.balloon_low   = 0;
 647         balloon_stats.balloon_high  = 0;
 648
 649         balloon_stats.schedule_delay = 1;
 650         balloon_stats.max_schedule_delay = 32;
 651         balloon_stats.retry_count = 1;
 652         balloon_stats.max_retry_count = RETRY_UNLIMITED;
 653
 654 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 655         balloon_stats.hotplug_pages = 0;
 656         balloon_stats.balloon_hotplug = 0;
 657
 658         set_online_page_callback(&xen_online_page);
 659         register_memory_notifier(&xen_memory_nb);
 660 #endif
 661
 662         /*
 663          * Initialize the balloon with pages from the extra memory
 664          * regions (see arch/x86/xen/setup.c).
 665          */
 666         for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
 667                 if (xen_extra_mem[i].size)
 668                         balloon_add_region(PFN_UP(xen_extra_mem[i].start),
 669                                            PFN_DOWN(xen_extra_mem[i].size));
 670
 671         return 0;
 672 }
 673
 674 subsys_initcall(balloon_init);
 675
 676 static int __init balloon_clear(void)
 677 {
 678         int cpu;
 679
 680         for_each_possible_cpu(cpu)
 681                 per_cpu(balloon_scratch_page, cpu) = NULL;
 682
 683         return 0;
 684 }
 685 early_initcall(balloon_clear);
 686
 687 MODULE_LICENSE("GPL");