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_next_page(struct page *page)
 161 {
 162         struct list_head *next = page->lru.next;
 163         if (next == &ballooned_pages)
 164                 return NULL;
 165         return list_entry(next, struct page, lru);
 166 }
 167
 168 static enum bp_state update_schedule(enum bp_state state)
 169 {
 170         if (state == BP_ECANCELED)
 171                 return BP_ECANCELED;
 172
 173         if (state == BP_DONE) {
 174                 balloon_stats.schedule_delay = 1;
 175                 balloon_stats.retry_count = 1;
 176                 return BP_DONE;
 177         }
 178
 179         ++balloon_stats.retry_count;
 180
 181         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
 182                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
 183                 balloon_stats.schedule_delay = 1;
 184                 balloon_stats.retry_count = 1;
 185                 return BP_ECANCELED;
 186         }
 187
 188         balloon_stats.schedule_delay <<= 1;
 189
 190         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
 191                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
 192
 193         return BP_EAGAIN;
 194 }
 195
 196 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 197 static long current_credit(void)
 198 {
 199         return balloon_stats.target_pages - balloon_stats.current_pages -
 200                 balloon_stats.hotplug_pages;
 201 }
 202
 203 static bool balloon_is_inflated(void)
 204 {
 205         if (balloon_stats.balloon_low || balloon_stats.balloon_high ||
 206                         balloon_stats.balloon_hotplug)
 207                 return true;
 208         else
 209                 return false;
 210 }
 211
 212 /*
 213  * reserve_additional_memory() adds memory region of size >= credit above
 214  * max_pfn. New region is section aligned and size is modified to be multiple
 215  * of section size. Those features allow optimal use of address space and
 216  * establish proper alignment when this function is called first time after
 217  * boot (last section not fully populated at boot time contains unused memory
 218  * pages with PG_reserved bit not set; online_pages_range() does not allow page
 219  * onlining in whole range if first onlined page does not have PG_reserved
 220  * bit set). Real size of added memory is established at page onlining stage.
 221  */
 222
 223 static enum bp_state reserve_additional_memory(long credit)
 224 {
 225         int nid, rc;
 226         u64 hotplug_start_paddr;
 227         unsigned long balloon_hotplug = credit;
 228
 229         hotplug_start_paddr = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
 230         balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
 231         nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
 232
 233         rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);
 234
 235         if (rc) {
 236                 pr_warn("Cannot add additional memory (%i)\n", rc);
 237                 return BP_ECANCELED;
 238         }
 239
 240         balloon_hotplug -= credit;
 241
 242         balloon_stats.hotplug_pages += credit;
 243         balloon_stats.balloon_hotplug = balloon_hotplug;
 244
 245         return BP_DONE;
 246 }
 247
 248 static void xen_online_page(struct page *page)
 249 {
 250         __online_page_set_limits(page);
 251
 252         mutex_lock(&balloon_mutex);
 253
 254         __balloon_append(page);
 255
 256         if (balloon_stats.hotplug_pages)
 257                 --balloon_stats.hotplug_pages;
 258         else
 259                 --balloon_stats.balloon_hotplug;
 260
 261         mutex_unlock(&balloon_mutex);
 262 }
 263
 264 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 265 {
 266         if (val == MEM_ONLINE)
 267                 schedule_delayed_work(&balloon_worker, 0);
 268
 269         return NOTIFY_OK;
 270 }
 271
 272 static struct notifier_block xen_memory_nb = {
 273         .notifier_call = xen_memory_notifier,
 274         .priority = 0
 275 };
 276 #else
 277 static long current_credit(void)
 278 {
 279         unsigned long target = balloon_stats.target_pages;
 280
 281         target = min(target,
 282                      balloon_stats.current_pages +
 283                      balloon_stats.balloon_low +
 284                      balloon_stats.balloon_high);
 285
 286         return target - balloon_stats.current_pages;
 287 }
 288
 289 static bool balloon_is_inflated(void)
 290 {
 291         if (balloon_stats.balloon_low || balloon_stats.balloon_high)
 292                 return true;
 293         else
 294                 return false;
 295 }
 296
 297 static enum bp_state reserve_additional_memory(long credit)
 298 {
 299         balloon_stats.target_pages = balloon_stats.current_pages;
 300         return BP_DONE;
 301 }
 302 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 303
 304 static enum bp_state increase_reservation(unsigned long nr_pages)
 305 {
 306         int rc;
 307         unsigned long  pfn, i;
 308         struct page   *page;
 309         struct xen_memory_reservation reservation = {
 310                 .address_bits = 0,
 311                 .extent_order = 0,
 312                 .domid        = DOMID_SELF
 313         };
 314
 315 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 316         if (!balloon_stats.balloon_low && !balloon_stats.balloon_high) {
 317                 nr_pages = min(nr_pages, balloon_stats.balloon_hotplug);
 318                 balloon_stats.hotplug_pages += nr_pages;
 319                 balloon_stats.balloon_hotplug -= nr_pages;
 320                 return BP_DONE;
 321         }
 322 #endif
 323
 324         if (nr_pages > ARRAY_SIZE(frame_list))
 325                 nr_pages = ARRAY_SIZE(frame_list);
 326
 327         page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
 328         for (i = 0; i < nr_pages; i++) {
 329                 if (!page) {
 330                         nr_pages = i;
 331                         break;
 332                 }
 333                 frame_list[i] = page_to_pfn(page);
 334                 page = balloon_next_page(page);
 335         }
 336
 337         set_xen_guest_handle(reservation.extent_start, frame_list);
 338         reservation.nr_extents = nr_pages;
 339         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 340         if (rc <= 0)
 341                 return BP_EAGAIN;
 342
 343         for (i = 0; i < rc; i++) {
 344                 page = balloon_retrieve(false);
 345                 BUG_ON(page == NULL);
 346
 347                 pfn = page_to_pfn(page);
 348
 349 #ifdef CONFIG_XEN_HAVE_PVMMU
 350                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 351                         set_phys_to_machine(pfn, frame_list[i]);
 352
 353                         /* Link back into the page tables if not highmem. */
 354                         if (!PageHighMem(page)) {
 355                                 int ret;
 356                                 ret = HYPERVISOR_update_va_mapping(
 357                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 358                                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 359                                                 0);
 360                                 BUG_ON(ret);
 361                         }
 362                 }
 363 #endif
 364
 365                 /* Relinquish the page back to the allocator. */
 366                 __free_reserved_page(page);
 367         }
 368
 369         balloon_stats.current_pages += rc;
 370
 371         return BP_DONE;
 372 }
 373
 374 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 375 {
 376         enum bp_state state = BP_DONE;
 377         unsigned long  pfn, i;
 378         struct page   *page;
 379         int ret;
 380         struct xen_memory_reservation reservation = {
 381                 .address_bits = 0,
 382                 .extent_order = 0,
 383                 .domid        = DOMID_SELF
 384         };
 385
 386 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 387         if (balloon_stats.hotplug_pages) {
 388                 nr_pages = min(nr_pages, balloon_stats.hotplug_pages);
 389                 balloon_stats.hotplug_pages -= nr_pages;
 390                 balloon_stats.balloon_hotplug += nr_pages;
 391                 return BP_DONE;
 392         }
 393 #endif
 394
 395         if (nr_pages > ARRAY_SIZE(frame_list))
 396                 nr_pages = ARRAY_SIZE(frame_list);
 397
 398         for (i = 0; i < nr_pages; i++) {
 399                 page = alloc_page(gfp);
 400                 if (page == NULL) {
 401                         nr_pages = i;
 402                         state = BP_EAGAIN;
 403                         break;
 404                 }
 405                 scrub_page(page);
 406
 407                 frame_list[i] = page_to_pfn(page);
 408         }
 409
 410         /*
 411          * Ensure that ballooned highmem pages don't have kmaps.
 412          *
 413          * Do this before changing the p2m as kmap_flush_unused()
 414          * reads PTEs to obtain pages (and hence needs the original
 415          * p2m entry).
 416          */
 417         kmap_flush_unused();
 418
 419         /* Update direct mapping, invalidate P2M, and add to balloon. */
 420         for (i = 0; i < nr_pages; i++) {
 421                 pfn = frame_list[i];
 422                 frame_list[i] = pfn_to_mfn(pfn);
 423                 page = pfn_to_page(pfn);
 424
 425 #ifdef CONFIG_XEN_HAVE_PVMMU
 426                 /*
 427                  * Ballooned out frames are effectively replaced with
 428                  * a scratch frame.  Ensure direct mappings and the
 429                  * p2m are consistent.
 430                  */
 431                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 432                         if (!PageHighMem(page)) {
 433                                 struct page *scratch_page = get_balloon_scratch_page();
 434
 435                                 ret = HYPERVISOR_update_va_mapping(
 436                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 437                                                 pfn_pte(page_to_pfn(scratch_page),
 438                                                         PAGE_KERNEL_RO), 0);
 439                                 BUG_ON(ret);
 440
 441                                 put_balloon_scratch_page();
 442                         }
 443                         __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 444                 }
 445 #endif
 446
 447                 balloon_append(page);
 448         }
 449
 450         flush_tlb_all();
 451
 452         set_xen_guest_handle(reservation.extent_start, frame_list);
 453         reservation.nr_extents   = nr_pages;
 454         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 455         BUG_ON(ret != nr_pages);
 456
 457         balloon_stats.current_pages -= nr_pages;
 458
 459         return state;
 460 }
 461
 462 /*
 463  * We avoid multiple worker processes conflicting via the balloon mutex.
 464  * We may of course race updates of the target counts (which are protected
 465  * by the balloon lock), or with changes to the Xen hard limit, but we will
 466  * recover from these in time.
 467  */
 468 static void balloon_process(struct work_struct *work)
 469 {
 470         enum bp_state state = BP_DONE;
 471         long credit;
 472
 473         mutex_lock(&balloon_mutex);
 474
 475         do {
 476                 credit = current_credit();
 477
 478                 if (credit > 0) {
 479                         if (balloon_is_inflated())
 480                                 state = increase_reservation(credit);
 481                         else
 482                                 state = reserve_additional_memory(credit);
 483                 }
 484
 485                 if (credit < 0)
 486                         state = decrease_reservation(-credit, GFP_BALLOON);
 487
 488                 state = update_schedule(state);
 489
 490 #ifndef CONFIG_PREEMPT
 491                 if (need_resched())
 492                         schedule();
 493 #endif
 494         } while (credit && state == BP_DONE);
 495
 496         /* Schedule more work if there is some still to be done. */
 497         if (state == BP_EAGAIN)
 498                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 499
 500         mutex_unlock(&balloon_mutex);
 501 }
 502
 503 struct page *get_balloon_scratch_page(void)
 504 {
 505         struct page *ret = get_cpu_var(balloon_scratch_page);
 506         BUG_ON(ret == NULL);
 507         return ret;
 508 }
 509
 510 void put_balloon_scratch_page(void)
 511 {
 512         put_cpu_var(balloon_scratch_page);
 513 }
 514
 515 /* Resets the Xen limit, sets new target, and kicks off processing. */
 516 void balloon_set_new_target(unsigned long target)
 517 {
 518         /* No need for lock. Not read-modify-write updates. */
 519         balloon_stats.target_pages = target;
 520         schedule_delayed_work(&balloon_worker, 0);
 521 }
 522 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 523
 524 /**
 525  * alloc_xenballooned_pages - get pages that have been ballooned out
 526  * @nr_pages: Number of pages to get
 527  * @pages: pages returned
 528  * @highmem: allow highmem pages
 529  * @return 0 on success, error otherwise
 530  */
 531 int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
 532 {
 533         int pgno = 0;
 534         struct page *page;
 535         mutex_lock(&balloon_mutex);
 536         while (pgno < nr_pages) {
 537                 page = balloon_retrieve(highmem);
 538                 if (page && (highmem || !PageHighMem(page))) {
 539                         pages[pgno++] = page;
 540                 } else {
 541                         enum bp_state st;
 542                         if (page)
 543                                 balloon_append(page);
 544                         st = decrease_reservation(nr_pages - pgno,
 545                                         highmem ? GFP_HIGHUSER : GFP_USER);
 546                         if (st != BP_DONE)
 547                                 goto out_undo;
 548                 }
 549         }
 550         mutex_unlock(&balloon_mutex);
 551         return 0;
 552  out_undo:
 553         while (pgno)
 554                 balloon_append(pages[--pgno]);
 555         /* Free the memory back to the kernel soon */
 556         schedule_delayed_work(&balloon_worker, 0);
 557         mutex_unlock(&balloon_mutex);
 558         return -ENOMEM;
 559 }
 560 EXPORT_SYMBOL(alloc_xenballooned_pages);
 561
 562 /**
 563  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
 564  * @nr_pages: Number of pages
 565  * @pages: pages to return
 566  */
 567 void free_xenballooned_pages(int nr_pages, struct page **pages)
 568 {
 569         int i;
 570
 571         mutex_lock(&balloon_mutex);
 572
 573         for (i = 0; i < nr_pages; i++) {
 574                 if (pages[i])
 575                         balloon_append(pages[i]);
 576         }
 577
 578         /* The balloon may be too large now. Shrink it if needed. */
 579         if (current_credit())
 580                 schedule_delayed_work(&balloon_worker, 0);
 581
 582         mutex_unlock(&balloon_mutex);
 583 }
 584 EXPORT_SYMBOL(free_xenballooned_pages);
 585
 586 static void __init balloon_add_region(unsigned long start_pfn,
 587                                       unsigned long pages)
 588 {
 589         unsigned long pfn, extra_pfn_end;
 590         struct page *page;
 591
 592         /*
 593          * If the amount of usable memory has been limited (e.g., with
 594          * the 'mem' command line parameter), don't add pages beyond
 595          * this limit.
 596          */
 597         extra_pfn_end = min(max_pfn, start_pfn + pages);
 598
 599         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
 600                 page = pfn_to_page(pfn);
 601                 /* totalram_pages and totalhigh_pages do not
 602                    include the boot-time balloon extension, so
 603                    don't subtract from it. */
 604                 __balloon_append(page);
 605         }
 606 }
 607
 608 static int alloc_balloon_scratch_page(int cpu)
 609 {
 610         if (per_cpu(balloon_scratch_page, cpu) != NULL)
 611                 return 0;
 612
 613         per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
 614         if (per_cpu(balloon_scratch_page, cpu) == NULL) {
 615                 pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
 616                 return -ENOMEM;
 617         }
 618
 619         return 0;
 620 }
 621
 622
 623 static int balloon_cpu_notify(struct notifier_block *self,
 624                                     unsigned long action, void *hcpu)
 625 {
 626         int cpu = (long)hcpu;
 627         switch (action) {
 628         case CPU_UP_PREPARE:
 629                 if (alloc_balloon_scratch_page(cpu))
 630                         return NOTIFY_BAD;
 631                 break;
 632         default:
 633                 break;
 634         }
 635         return NOTIFY_OK;
 636 }
 637
 638 static struct notifier_block balloon_cpu_notifier = {
 639         .notifier_call  = balloon_cpu_notify,
 640 };
 641
 642 static int __init balloon_init(void)
 643 {
 644         int i, cpu;
 645
 646         if (!xen_domain())
 647                 return -ENODEV;
 648
 649         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 650                 register_cpu_notifier(&balloon_cpu_notifier);
 651
 652                 get_online_cpus();
 653                 for_each_online_cpu(cpu) {
 654                         if (alloc_balloon_scratch_page(cpu)) {
 655                                 put_online_cpus();
 656                                 unregister_cpu_notifier(&balloon_cpu_notifier);
 657                                 return -ENOMEM;
 658                         }
 659                 }
 660                 put_online_cpus();
 661         }
 662
 663         pr_info("Initialising balloon driver\n");
 664
 665         balloon_stats.current_pages = xen_pv_domain()
 666                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
 667                 : get_num_physpages();
 668         balloon_stats.target_pages  = balloon_stats.current_pages;
 669         balloon_stats.balloon_low   = 0;
 670         balloon_stats.balloon_high  = 0;
 671
 672         balloon_stats.schedule_delay = 1;
 673         balloon_stats.max_schedule_delay = 32;
 674         balloon_stats.retry_count = 1;
 675         balloon_stats.max_retry_count = RETRY_UNLIMITED;
 676
 677 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 678         balloon_stats.hotplug_pages = 0;
 679         balloon_stats.balloon_hotplug = 0;
 680
 681         set_online_page_callback(&xen_online_page);
 682         register_memory_notifier(&xen_memory_nb);
 683 #endif
 684
 685         /*
 686          * Initialize the balloon with pages from the extra memory
 687          * regions (see arch/x86/xen/setup.c).
 688          */
 689         for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
 690                 if (xen_extra_mem[i].size)
 691                         balloon_add_region(PFN_UP(xen_extra_mem[i].start),
 692                                            PFN_DOWN(xen_extra_mem[i].size));
 693
 694         return 0;
 695 }
 696
 697 subsys_initcall(balloon_init);
 698
 699 static int __init balloon_clear(void)
 700 {
 701         int cpu;
 702
 703         for_each_possible_cpu(cpu)
 704                 per_cpu(balloon_scratch_page, cpu) = NULL;
 705
 706         return 0;
 707 }
 708 early_initcall(balloon_clear);
 709
 710 MODULE_LICENSE("GPL");