drivers/xen/balloon.c

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