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/mm.h> 46 #include <linux/bootmem.h> 47 #include <linux/pagemap.h> 48 #include <linux/highmem.h> 49 #include <linux/mutex.h> 50 #include <linux/list.h> 51 #include <linux/gfp.h> 52 #include <linux/notifier.h> 53 #include <linux/memory.h> 54 #include <linux/memory_hotplug.h> 55 #include <linux/percpu-defs.h> 56 #include <linux/slab.h> 57 #include <linux/sysctl.h> 58 59 #include <asm/page.h> 60 #include <asm/pgalloc.h> 61 #include <asm/pgtable.h> 62 #include <asm/tlb.h> 63 64 #include <asm/xen/hypervisor.h> 65 #include <asm/xen/hypercall.h> 66 67 #include <xen/xen.h> 68 #include <xen/interface/xen.h> 69 #include <xen/interface/memory.h> 70 #include <xen/balloon.h> 71 #include <xen/features.h> 72 #include <xen/page.h> 73 74 static int xen_hotplug_unpopulated; 75 76 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG 77 78 static int zero; 79 static int one = 1; 80 81 static struct ctl_table balloon_table[] = { 82 { 83 .procname = "hotplug_unpopulated", 84 .data = &xen_hotplug_unpopulated, 85 .maxlen = sizeof(int), 86 .mode = 0644, 87 .proc_handler = proc_dointvec_minmax, 88 .extra1 = &zero, 89 .extra2 = &one, 90 }, 91 { } 92 }; 93 94 static struct ctl_table balloon_root[] = { 95 { 96 .procname = "balloon", 97 .mode = 0555, 98 .child = balloon_table, 99 }, 100 { } 101 }; 102 103 static struct ctl_table xen_root[] = { 104 { 105 .procname = "xen", 106 .mode = 0555, 107 .child = balloon_root, 108 }, 109 { } 110 }; 111 112 #endif 113 114 /* 115 * Use one extent per PAGE_SIZE to avoid to break down the page into 116 * multiple frame. 117 */ 118 #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1) 119 120 /* 121 * balloon_process() state: 122 * 123 * BP_DONE: done or nothing to do, 124 * BP_WAIT: wait to be rescheduled, 125 * BP_EAGAIN: error, go to sleep, 126 * BP_ECANCELED: error, balloon operation canceled. 127 */ 128 129 enum bp_state { 130 BP_DONE, 131 BP_WAIT, 132 BP_EAGAIN, 133 BP_ECANCELED 134 }; 135 136 137 static DEFINE_MUTEX(balloon_mutex); 138 139 struct balloon_stats balloon_stats; 140 EXPORT_SYMBOL_GPL(balloon_stats); 141 142 /* We increase/decrease in batches which fit in a page */ 143 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)]; 144 145 146 /* List of ballooned pages, threaded through the mem_map array. */ 147 static LIST_HEAD(ballooned_pages); 148 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq); 149 150 /* Main work function, always executed in process context. */ 151 static void balloon_process(struct work_struct *work); 152 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process); 153 154 static void release_memory_resource(struct resource *resource); 155 156 /* When ballooning out (allocating memory to return to Xen) we don't really 157 want the kernel to try too hard since that can trigger the oom killer. */ 158 #define GFP_BALLOON \ 159 (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC) 160 161 static void scrub_page(struct page *page) 162 { 163 #ifdef CONFIG_XEN_SCRUB_PAGES 164 clear_highpage(page); 165 #endif 166 } 167 168 /* balloon_append: add the given page to the balloon. */ 169 static void __balloon_append(struct page *page) 170 { 171 /* Lowmem is re-populated first, so highmem pages go at list tail. */ 172 if (PageHighMem(page)) { 173 list_add_tail(&page->lru, &ballooned_pages); 174 balloon_stats.balloon_high++; 175 } else { 176 list_add(&page->lru, &ballooned_pages); 177 balloon_stats.balloon_low++; 178 } 179 wake_up(&balloon_wq); 180 } 181 182 static void balloon_append(struct page *page) 183 { 184 __balloon_append(page); 185 adjust_managed_page_count(page, -1); 186 } 187 188 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */ 189 static struct page *balloon_retrieve(bool require_lowmem) 190 { 191 struct page *page; 192 193 if (list_empty(&ballooned_pages)) 194 return NULL; 195 196 page = list_entry(ballooned_pages.next, struct page, lru); 197 if (require_lowmem && PageHighMem(page)) 198 return NULL; 199 list_del(&page->lru); 200 201 if (PageHighMem(page)) 202 balloon_stats.balloon_high--; 203 else 204 balloon_stats.balloon_low--; 205 206 adjust_managed_page_count(page, 1); 207 208 return page; 209 } 210 211 static struct page *balloon_next_page(struct page *page) 212 { 213 struct list_head *next = page->lru.next; 214 if (next == &ballooned_pages) 215 return NULL; 216 return list_entry(next, struct page, lru); 217 } 218 219 static enum bp_state update_schedule(enum bp_state state) 220 { 221 if (state == BP_WAIT) 222 return BP_WAIT; 223 224 if (state == BP_ECANCELED) 225 return BP_ECANCELED; 226 227 if (state == BP_DONE) { 228 balloon_stats.schedule_delay = 1; 229 balloon_stats.retry_count = 1; 230 return BP_DONE; 231 } 232 233 ++balloon_stats.retry_count; 234 235 if (balloon_stats.max_retry_count != RETRY_UNLIMITED && 236 balloon_stats.retry_count > balloon_stats.max_retry_count) { 237 balloon_stats.schedule_delay = 1; 238 balloon_stats.retry_count = 1; 239 return BP_ECANCELED; 240 } 241 242 balloon_stats.schedule_delay <<= 1; 243 244 if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay) 245 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay; 246 247 return BP_EAGAIN; 248 } 249 250 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG 251 static struct resource *additional_memory_resource(phys_addr_t size) 252 { 253 struct resource *res; 254 int ret; 255 256 res = kzalloc(sizeof(*res), GFP_KERNEL); 257 if (!res) 258 return NULL; 259 260 res->name = "System RAM"; 261 res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY; 262 263 ret = allocate_resource(&iomem_resource, res, 264 size, 0, -1, 265 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); 266 if (ret < 0) { 267 pr_err("Cannot allocate new System RAM resource\n"); 268 kfree(res); 269 return NULL; 270 } 271 272 #ifdef CONFIG_SPARSEMEM 273 { 274 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT); 275 unsigned long pfn = res->start >> PAGE_SHIFT; 276 277 if (pfn > limit) { 278 pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n", 279 pfn, limit); 280 release_memory_resource(res); 281 return NULL; 282 } 283 } 284 #endif 285 286 return res; 287 } 288 289 static void release_memory_resource(struct resource *resource) 290 { 291 if (!resource) 292 return; 293 294 /* 295 * No need to reset region to identity mapped since we now 296 * know that no I/O can be in this region 297 */ 298 release_resource(resource); 299 kfree(resource); 300 } 301 302 static enum bp_state reserve_additional_memory(void) 303 { 304 long credit; 305 struct resource *resource; 306 int nid, rc; 307 unsigned long balloon_hotplug; 308 309 credit = balloon_stats.target_pages + balloon_stats.target_unpopulated 310 - balloon_stats.total_pages; 311 312 /* 313 * Already hotplugged enough pages? Wait for them to be 314 * onlined. 315 */ 316 if (credit <= 0) 317 return BP_WAIT; 318 319 balloon_hotplug = round_up(credit, PAGES_PER_SECTION); 320 321 resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE); 322 if (!resource) 323 goto err; 324 325 nid = memory_add_physaddr_to_nid(resource->start); 326 327 #ifdef CONFIG_XEN_HAVE_PVMMU 328 /* 329 * We don't support PV MMU when Linux and Xen is using 330 * different page granularity. 331 */ 332 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); 333 334 /* 335 * add_memory() will build page tables for the new memory so 336 * the p2m must contain invalid entries so the correct 337 * non-present PTEs will be written. 338 * 339 * If a failure occurs, the original (identity) p2m entries 340 * are not restored since this region is now known not to 341 * conflict with any devices. 342 */ 343 if (!xen_feature(XENFEAT_auto_translated_physmap)) { 344 unsigned long pfn, i; 345 346 pfn = PFN_DOWN(resource->start); 347 for (i = 0; i < balloon_hotplug; i++) { 348 if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) { 349 pr_warn("set_phys_to_machine() failed, no memory added\n"); 350 goto err; 351 } 352 } 353 } 354 #endif 355 356 /* 357 * add_memory_resource() will call online_pages() which in its turn 358 * will call xen_online_page() callback causing deadlock if we don't 359 * release balloon_mutex here. Unlocking here is safe because the 360 * callers drop the mutex before trying again. 361 */ 362 mutex_unlock(&balloon_mutex); 363 rc = add_memory_resource(nid, resource, memhp_auto_online); 364 mutex_lock(&balloon_mutex); 365 366 if (rc) { 367 pr_warn("Cannot add additional memory (%i)\n", rc); 368 goto err; 369 } 370 371 balloon_stats.total_pages += balloon_hotplug; 372 373 return BP_WAIT; 374 err: 375 release_memory_resource(resource); 376 return BP_ECANCELED; 377 } 378 379 static void xen_online_page(struct page *page) 380 { 381 __online_page_set_limits(page); 382 383 mutex_lock(&balloon_mutex); 384 385 __balloon_append(page); 386 387 mutex_unlock(&balloon_mutex); 388 } 389 390 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v) 391 { 392 if (val == MEM_ONLINE) 393 schedule_delayed_work(&balloon_worker, 0); 394 395 return NOTIFY_OK; 396 } 397 398 static struct notifier_block xen_memory_nb = { 399 .notifier_call = xen_memory_notifier, 400 .priority = 0 401 }; 402 #else 403 static enum bp_state reserve_additional_memory(void) 404 { 405 balloon_stats.target_pages = balloon_stats.current_pages; 406 return BP_ECANCELED; 407 } 408 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */ 409 410 static long current_credit(void) 411 { 412 return balloon_stats.target_pages - balloon_stats.current_pages; 413 } 414 415 static bool balloon_is_inflated(void) 416 { 417 return balloon_stats.balloon_low || balloon_stats.balloon_high; 418 } 419 420 static enum bp_state increase_reservation(unsigned long nr_pages) 421 { 422 int rc; 423 unsigned long i; 424 struct page *page; 425 struct xen_memory_reservation reservation = { 426 .address_bits = 0, 427 .extent_order = EXTENT_ORDER, 428 .domid = DOMID_SELF 429 }; 430 431 if (nr_pages > ARRAY_SIZE(frame_list)) 432 nr_pages = ARRAY_SIZE(frame_list); 433 434 page = list_first_entry_or_null(&ballooned_pages, struct page, lru); 435 for (i = 0; i < nr_pages; i++) { 436 if (!page) { 437 nr_pages = i; 438 break; 439 } 440 441 /* XENMEM_populate_physmap requires a PFN based on Xen 442 * granularity. 443 */ 444 frame_list[i] = page_to_xen_pfn(page); 445 page = balloon_next_page(page); 446 } 447 448 set_xen_guest_handle(reservation.extent_start, frame_list); 449 reservation.nr_extents = nr_pages; 450 rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation); 451 if (rc <= 0) 452 return BP_EAGAIN; 453 454 for (i = 0; i < rc; i++) { 455 page = balloon_retrieve(false); 456 BUG_ON(page == NULL); 457 458 #ifdef CONFIG_XEN_HAVE_PVMMU 459 /* 460 * We don't support PV MMU when Linux and Xen is using 461 * different page granularity. 462 */ 463 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); 464 465 if (!xen_feature(XENFEAT_auto_translated_physmap)) { 466 unsigned long pfn = page_to_pfn(page); 467 468 set_phys_to_machine(pfn, frame_list[i]); 469 470 /* Link back into the page tables if not highmem. */ 471 if (!PageHighMem(page)) { 472 int ret; 473 ret = HYPERVISOR_update_va_mapping( 474 (unsigned long)__va(pfn << PAGE_SHIFT), 475 mfn_pte(frame_list[i], PAGE_KERNEL), 476 0); 477 BUG_ON(ret); 478 } 479 } 480 #endif 481 482 /* Relinquish the page back to the allocator. */ 483 __free_reserved_page(page); 484 } 485 486 balloon_stats.current_pages += rc; 487 488 return BP_DONE; 489 } 490 491 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) 492 { 493 enum bp_state state = BP_DONE; 494 unsigned long i; 495 struct page *page, *tmp; 496 int ret; 497 struct xen_memory_reservation reservation = { 498 .address_bits = 0, 499 .extent_order = EXTENT_ORDER, 500 .domid = DOMID_SELF 501 }; 502 LIST_HEAD(pages); 503 504 if (nr_pages > ARRAY_SIZE(frame_list)) 505 nr_pages = ARRAY_SIZE(frame_list); 506 507 for (i = 0; i < nr_pages; i++) { 508 page = alloc_page(gfp); 509 if (page == NULL) { 510 nr_pages = i; 511 state = BP_EAGAIN; 512 break; 513 } 514 scrub_page(page); 515 list_add(&page->lru, &pages); 516 } 517 518 /* 519 * Ensure that ballooned highmem pages don't have kmaps. 520 * 521 * Do this before changing the p2m as kmap_flush_unused() 522 * reads PTEs to obtain pages (and hence needs the original 523 * p2m entry). 524 */ 525 kmap_flush_unused(); 526 527 /* 528 * Setup the frame, update direct mapping, invalidate P2M, 529 * and add to balloon. 530 */ 531 i = 0; 532 list_for_each_entry_safe(page, tmp, &pages, lru) { 533 /* XENMEM_decrease_reservation requires a GFN */ 534 frame_list[i++] = xen_page_to_gfn(page); 535 536 #ifdef CONFIG_XEN_HAVE_PVMMU 537 /* 538 * We don't support PV MMU when Linux and Xen is using 539 * different page granularity. 540 */ 541 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); 542 543 if (!xen_feature(XENFEAT_auto_translated_physmap)) { 544 unsigned long pfn = page_to_pfn(page); 545 546 if (!PageHighMem(page)) { 547 ret = HYPERVISOR_update_va_mapping( 548 (unsigned long)__va(pfn << PAGE_SHIFT), 549 __pte_ma(0), 0); 550 BUG_ON(ret); 551 } 552 __set_phys_to_machine(pfn, INVALID_P2M_ENTRY); 553 } 554 #endif 555 list_del(&page->lru); 556 557 balloon_append(page); 558 } 559 560 flush_tlb_all(); 561 562 set_xen_guest_handle(reservation.extent_start, frame_list); 563 reservation.nr_extents = nr_pages; 564 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation); 565 BUG_ON(ret != nr_pages); 566 567 balloon_stats.current_pages -= nr_pages; 568 569 return state; 570 } 571 572 /* 573 * As this is a work item it is guaranteed to run as a single instance only. 574 * We may of course race updates of the target counts (which are protected 575 * by the balloon lock), or with changes to the Xen hard limit, but we will 576 * recover from these in time. 577 */ 578 static void balloon_process(struct work_struct *work) 579 { 580 enum bp_state state = BP_DONE; 581 long credit; 582 583 584 do { 585 mutex_lock(&balloon_mutex); 586 587 credit = current_credit(); 588 589 if (credit > 0) { 590 if (balloon_is_inflated()) 591 state = increase_reservation(credit); 592 else 593 state = reserve_additional_memory(); 594 } 595 596 if (credit < 0) 597 state = decrease_reservation(-credit, GFP_BALLOON); 598 599 state = update_schedule(state); 600 601 mutex_unlock(&balloon_mutex); 602 603 cond_resched(); 604 605 } while (credit && state == BP_DONE); 606 607 /* Schedule more work if there is some still to be done. */ 608 if (state == BP_EAGAIN) 609 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ); 610 } 611 612 /* Resets the Xen limit, sets new target, and kicks off processing. */ 613 void balloon_set_new_target(unsigned long target) 614 { 615 /* No need for lock. Not read-modify-write updates. */ 616 balloon_stats.target_pages = target; 617 schedule_delayed_work(&balloon_worker, 0); 618 } 619 EXPORT_SYMBOL_GPL(balloon_set_new_target); 620 621 static int add_ballooned_pages(int nr_pages) 622 { 623 enum bp_state st; 624 625 if (xen_hotplug_unpopulated) { 626 st = reserve_additional_memory(); 627 if (st != BP_ECANCELED) { 628 mutex_unlock(&balloon_mutex); 629 wait_event(balloon_wq, 630 !list_empty(&ballooned_pages)); 631 mutex_lock(&balloon_mutex); 632 return 0; 633 } 634 } 635 636 st = decrease_reservation(nr_pages, GFP_USER); 637 if (st != BP_DONE) 638 return -ENOMEM; 639 640 return 0; 641 } 642 643 /** 644 * alloc_xenballooned_pages - get pages that have been ballooned out 645 * @nr_pages: Number of pages to get 646 * @pages: pages returned 647 * @return 0 on success, error otherwise 648 */ 649 int alloc_xenballooned_pages(int nr_pages, struct page **pages) 650 { 651 int pgno = 0; 652 struct page *page; 653 int ret; 654 655 mutex_lock(&balloon_mutex); 656 657 balloon_stats.target_unpopulated += nr_pages; 658 659 while (pgno < nr_pages) { 660 page = balloon_retrieve(true); 661 if (page) { 662 pages[pgno++] = page; 663 #ifdef CONFIG_XEN_HAVE_PVMMU 664 /* 665 * We don't support PV MMU when Linux and Xen is using 666 * different page granularity. 667 */ 668 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); 669 670 ret = xen_alloc_p2m_entry(page_to_pfn(page)); 671 if (ret < 0) 672 goto out_undo; 673 #endif 674 } else { 675 ret = add_ballooned_pages(nr_pages - pgno); 676 if (ret < 0) 677 goto out_undo; 678 } 679 } 680 mutex_unlock(&balloon_mutex); 681 return 0; 682 out_undo: 683 mutex_unlock(&balloon_mutex); 684 free_xenballooned_pages(pgno, pages); 685 return ret; 686 } 687 EXPORT_SYMBOL(alloc_xenballooned_pages); 688 689 /** 690 * free_xenballooned_pages - return pages retrieved with get_ballooned_pages 691 * @nr_pages: Number of pages 692 * @pages: pages to return 693 */ 694 void free_xenballooned_pages(int nr_pages, struct page **pages) 695 { 696 int i; 697 698 mutex_lock(&balloon_mutex); 699 700 for (i = 0; i < nr_pages; i++) { 701 if (pages[i]) 702 balloon_append(pages[i]); 703 } 704 705 balloon_stats.target_unpopulated -= nr_pages; 706 707 /* The balloon may be too large now. Shrink it if needed. */ 708 if (current_credit()) 709 schedule_delayed_work(&balloon_worker, 0); 710 711 mutex_unlock(&balloon_mutex); 712 } 713 EXPORT_SYMBOL(free_xenballooned_pages); 714 715 static void __init balloon_add_region(unsigned long start_pfn, 716 unsigned long pages) 717 { 718 unsigned long pfn, extra_pfn_end; 719 struct page *page; 720 721 /* 722 * If the amount of usable memory has been limited (e.g., with 723 * the 'mem' command line parameter), don't add pages beyond 724 * this limit. 725 */ 726 extra_pfn_end = min(max_pfn, start_pfn + pages); 727 728 for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) { 729 page = pfn_to_page(pfn); 730 /* totalram_pages and totalhigh_pages do not 731 include the boot-time balloon extension, so 732 don't subtract from it. */ 733 __balloon_append(page); 734 } 735 736 balloon_stats.total_pages += extra_pfn_end - start_pfn; 737 } 738 739 static int __init balloon_init(void) 740 { 741 int i; 742 743 if (!xen_domain()) 744 return -ENODEV; 745 746 pr_info("Initialising balloon driver\n"); 747 748 balloon_stats.current_pages = xen_pv_domain() 749 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn) 750 : get_num_physpages(); 751 balloon_stats.target_pages = balloon_stats.current_pages; 752 balloon_stats.balloon_low = 0; 753 balloon_stats.balloon_high = 0; 754 balloon_stats.total_pages = balloon_stats.current_pages; 755 756 balloon_stats.schedule_delay = 1; 757 balloon_stats.max_schedule_delay = 32; 758 balloon_stats.retry_count = 1; 759 balloon_stats.max_retry_count = RETRY_UNLIMITED; 760 761 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG 762 set_online_page_callback(&xen_online_page); 763 register_memory_notifier(&xen_memory_nb); 764 register_sysctl_table(xen_root); 765 #endif 766 767 /* 768 * Initialize the balloon with pages from the extra memory 769 * regions (see arch/x86/xen/setup.c). 770 */ 771 for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) 772 if (xen_extra_mem[i].n_pfns) 773 balloon_add_region(xen_extra_mem[i].start_pfn, 774 xen_extra_mem[i].n_pfns); 775 776 return 0; 777 } 778 subsys_initcall(balloon_init); 779