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