a6d4378eb8d9fc8aeea4fe1961f5c0f030ce2060
[muen/linux.git] / 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/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 #include <linux/slab.h>
58 #include <linux/sysctl.h>
59
60 #include <asm/page.h>
61 #include <asm/pgalloc.h>
62 #include <asm/pgtable.h>
63 #include <asm/tlb.h>
64
65 #include <asm/xen/hypervisor.h>
66 #include <asm/xen/hypercall.h>
67
68 #include <xen/xen.h>
69 #include <xen/interface/xen.h>
70 #include <xen/interface/memory.h>
71 #include <xen/balloon.h>
72 #include <xen/features.h>
73 #include <xen/page.h>
74
75 static int xen_hotplug_unpopulated;
76
77 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
78
79 static int zero;
80 static int one = 1;
81
82 static struct ctl_table balloon_table[] = {
83         {
84                 .procname       = "hotplug_unpopulated",
85                 .data           = &xen_hotplug_unpopulated,
86                 .maxlen         = sizeof(int),
87                 .mode           = 0644,
88                 .proc_handler   = proc_dointvec_minmax,
89                 .extra1         = &zero,
90                 .extra2         = &one,
91         },
92         { }
93 };
94
95 static struct ctl_table balloon_root[] = {
96         {
97                 .procname       = "balloon",
98                 .mode           = 0555,
99                 .child          = balloon_table,
100         },
101         { }
102 };
103
104 static struct ctl_table xen_root[] = {
105         {
106                 .procname       = "xen",
107                 .mode           = 0555,
108                 .child          = balloon_root,
109         },
110         { }
111 };
112
113 #endif
114
115 /*
116  * Use one extent per PAGE_SIZE to avoid to break down the page into
117  * multiple frame.
118  */
119 #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
120
121 /*
122  * balloon_process() state:
123  *
124  * BP_DONE: done or nothing to do,
125  * BP_WAIT: wait to be rescheduled,
126  * BP_EAGAIN: error, go to sleep,
127  * BP_ECANCELED: error, balloon operation canceled.
128  */
129
130 enum bp_state {
131         BP_DONE,
132         BP_WAIT,
133         BP_EAGAIN,
134         BP_ECANCELED
135 };
136
137
138 static DEFINE_MUTEX(balloon_mutex);
139
140 struct balloon_stats balloon_stats;
141 EXPORT_SYMBOL_GPL(balloon_stats);
142
143 /* We increase/decrease in batches which fit in a page */
144 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
145
146
147 /* List of ballooned pages, threaded through the mem_map array. */
148 static LIST_HEAD(ballooned_pages);
149 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
150
151 /* Main work function, always executed in process context. */
152 static void balloon_process(struct work_struct *work);
153 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
154
155 /* When ballooning out (allocating memory to return to Xen) we don't really
156    want the kernel to try too hard since that can trigger the oom killer. */
157 #define GFP_BALLOON \
158         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
159
160 static void scrub_page(struct page *page)
161 {
162 #ifdef CONFIG_XEN_SCRUB_PAGES
163         clear_highpage(page);
164 #endif
165 }
166
167 /* balloon_append: add the given page to the balloon. */
168 static void __balloon_append(struct page *page)
169 {
170         /* Lowmem is re-populated first, so highmem pages go at list tail. */
171         if (PageHighMem(page)) {
172                 list_add_tail(&page->lru, &ballooned_pages);
173                 balloon_stats.balloon_high++;
174         } else {
175                 list_add(&page->lru, &ballooned_pages);
176                 balloon_stats.balloon_low++;
177         }
178         wake_up(&balloon_wq);
179 }
180
181 static void balloon_append(struct page *page)
182 {
183         __balloon_append(page);
184 }
185
186 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
187 static struct page *balloon_retrieve(bool require_lowmem)
188 {
189         struct page *page;
190
191         if (list_empty(&ballooned_pages))
192                 return NULL;
193
194         page = list_entry(ballooned_pages.next, struct page, lru);
195         if (require_lowmem && PageHighMem(page))
196                 return NULL;
197         list_del(&page->lru);
198
199         if (PageHighMem(page))
200                 balloon_stats.balloon_high--;
201         else
202                 balloon_stats.balloon_low--;
203
204         return page;
205 }
206
207 static struct page *balloon_next_page(struct page *page)
208 {
209         struct list_head *next = page->lru.next;
210         if (next == &ballooned_pages)
211                 return NULL;
212         return list_entry(next, struct page, lru);
213 }
214
215 static enum bp_state update_schedule(enum bp_state state)
216 {
217         if (state == BP_WAIT)
218                 return BP_WAIT;
219
220         if (state == BP_ECANCELED)
221                 return BP_ECANCELED;
222
223         if (state == BP_DONE) {
224                 balloon_stats.schedule_delay = 1;
225                 balloon_stats.retry_count = 1;
226                 return BP_DONE;
227         }
228
229         ++balloon_stats.retry_count;
230
231         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
232                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
233                 balloon_stats.schedule_delay = 1;
234                 balloon_stats.retry_count = 1;
235                 return BP_ECANCELED;
236         }
237
238         balloon_stats.schedule_delay <<= 1;
239
240         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
241                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
242
243         return BP_EAGAIN;
244 }
245
246 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
247 static void release_memory_resource(struct resource *resource)
248 {
249         if (!resource)
250                 return;
251
252         /*
253          * No need to reset region to identity mapped since we now
254          * know that no I/O can be in this region
255          */
256         release_resource(resource);
257         kfree(resource);
258 }
259
260 static struct resource *additional_memory_resource(phys_addr_t size)
261 {
262         struct resource *res;
263         int ret;
264
265         res = kzalloc(sizeof(*res), GFP_KERNEL);
266         if (!res)
267                 return NULL;
268
269         res->name = "System RAM";
270         res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
271
272         ret = allocate_resource(&iomem_resource, res,
273                                 size, 0, -1,
274                                 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
275         if (ret < 0) {
276                 pr_err("Cannot allocate new System RAM resource\n");
277                 kfree(res);
278                 return NULL;
279         }
280
281 #ifdef CONFIG_SPARSEMEM
282         {
283                 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
284                 unsigned long pfn = res->start >> PAGE_SHIFT;
285
286                 if (pfn > limit) {
287                         pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n",
288                                pfn, limit);
289                         release_memory_resource(res);
290                         return NULL;
291                 }
292         }
293 #endif
294
295         return res;
296 }
297
298 static enum bp_state reserve_additional_memory(void)
299 {
300         long credit;
301         struct resource *resource;
302         int nid, rc;
303         unsigned long balloon_hotplug;
304
305         credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
306                 - balloon_stats.total_pages;
307
308         /*
309          * Already hotplugged enough pages?  Wait for them to be
310          * onlined.
311          */
312         if (credit <= 0)
313                 return BP_WAIT;
314
315         balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
316
317         resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
318         if (!resource)
319                 goto err;
320
321         nid = memory_add_physaddr_to_nid(resource->start);
322
323 #ifdef CONFIG_XEN_HAVE_PVMMU
324         /*
325          * We don't support PV MMU when Linux and Xen is using
326          * different page granularity.
327          */
328         BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
329
330         /*
331          * add_memory() will build page tables for the new memory so
332          * the p2m must contain invalid entries so the correct
333          * non-present PTEs will be written.
334          *
335          * If a failure occurs, the original (identity) p2m entries
336          * are not restored since this region is now known not to
337          * conflict with any devices.
338          */ 
339         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
340                 unsigned long pfn, i;
341
342                 pfn = PFN_DOWN(resource->start);
343                 for (i = 0; i < balloon_hotplug; i++) {
344                         if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
345                                 pr_warn("set_phys_to_machine() failed, no memory added\n");
346                                 goto err;
347                         }
348                 }
349         }
350 #endif
351
352         /*
353          * add_memory_resource() will call online_pages() which in its turn
354          * will call xen_online_page() callback causing deadlock if we don't
355          * release balloon_mutex here. Unlocking here is safe because the
356          * callers drop the mutex before trying again.
357          */
358         mutex_unlock(&balloon_mutex);
359         rc = add_memory_resource(nid, resource, memhp_auto_online);
360         mutex_lock(&balloon_mutex);
361
362         if (rc) {
363                 pr_warn("Cannot add additional memory (%i)\n", rc);
364                 goto err;
365         }
366
367         balloon_stats.total_pages += balloon_hotplug;
368
369         return BP_WAIT;
370   err:
371         release_memory_resource(resource);
372         return BP_ECANCELED;
373 }
374
375 static void xen_online_page(struct page *page)
376 {
377         __online_page_set_limits(page);
378
379         mutex_lock(&balloon_mutex);
380
381         __balloon_append(page);
382
383         mutex_unlock(&balloon_mutex);
384 }
385
386 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
387 {
388         if (val == MEM_ONLINE)
389                 schedule_delayed_work(&balloon_worker, 0);
390
391         return NOTIFY_OK;
392 }
393
394 static struct notifier_block xen_memory_nb = {
395         .notifier_call = xen_memory_notifier,
396         .priority = 0
397 };
398 #else
399 static enum bp_state reserve_additional_memory(void)
400 {
401         balloon_stats.target_pages = balloon_stats.current_pages;
402         return BP_ECANCELED;
403 }
404 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
405
406 static long current_credit(void)
407 {
408         return balloon_stats.target_pages - balloon_stats.current_pages;
409 }
410
411 static bool balloon_is_inflated(void)
412 {
413         return balloon_stats.balloon_low || balloon_stats.balloon_high;
414 }
415
416 static enum bp_state increase_reservation(unsigned long nr_pages)
417 {
418         int rc;
419         unsigned long i;
420         struct page   *page;
421         struct xen_memory_reservation reservation = {
422                 .address_bits = 0,
423                 .extent_order = EXTENT_ORDER,
424                 .domid        = DOMID_SELF
425         };
426
427         if (nr_pages > ARRAY_SIZE(frame_list))
428                 nr_pages = ARRAY_SIZE(frame_list);
429
430         page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
431         for (i = 0; i < nr_pages; i++) {
432                 if (!page) {
433                         nr_pages = i;
434                         break;
435                 }
436
437                 /* XENMEM_populate_physmap requires a PFN based on Xen
438                  * granularity.
439                  */
440                 frame_list[i] = page_to_xen_pfn(page);
441                 page = balloon_next_page(page);
442         }
443
444         set_xen_guest_handle(reservation.extent_start, frame_list);
445         reservation.nr_extents = nr_pages;
446         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
447         if (rc <= 0)
448                 return BP_EAGAIN;
449
450         for (i = 0; i < rc; i++) {
451                 page = balloon_retrieve(false);
452                 BUG_ON(page == NULL);
453
454 #ifdef CONFIG_XEN_HAVE_PVMMU
455                 /*
456                  * We don't support PV MMU when Linux and Xen is using
457                  * different page granularity.
458                  */
459                 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
460
461                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
462                         unsigned long pfn = page_to_pfn(page);
463
464                         set_phys_to_machine(pfn, frame_list[i]);
465
466                         /* Link back into the page tables if not highmem. */
467                         if (!PageHighMem(page)) {
468                                 int ret;
469                                 ret = HYPERVISOR_update_va_mapping(
470                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
471                                                 mfn_pte(frame_list[i], PAGE_KERNEL),
472                                                 0);
473                                 BUG_ON(ret);
474                         }
475                 }
476 #endif
477
478                 /* Relinquish the page back to the allocator. */
479                 free_reserved_page(page);
480         }
481
482         balloon_stats.current_pages += rc;
483
484         return BP_DONE;
485 }
486
487 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
488 {
489         enum bp_state state = BP_DONE;
490         unsigned long i;
491         struct page *page, *tmp;
492         int ret;
493         struct xen_memory_reservation reservation = {
494                 .address_bits = 0,
495                 .extent_order = EXTENT_ORDER,
496                 .domid        = DOMID_SELF
497         };
498         LIST_HEAD(pages);
499
500         if (nr_pages > ARRAY_SIZE(frame_list))
501                 nr_pages = ARRAY_SIZE(frame_list);
502
503         for (i = 0; i < nr_pages; i++) {
504                 page = alloc_page(gfp);
505                 if (page == NULL) {
506                         nr_pages = i;
507                         state = BP_EAGAIN;
508                         break;
509                 }
510                 adjust_managed_page_count(page, -1);
511                 scrub_page(page);
512                 list_add(&page->lru, &pages);
513         }
514
515         /*
516          * Ensure that ballooned highmem pages don't have kmaps.
517          *
518          * Do this before changing the p2m as kmap_flush_unused()
519          * reads PTEs to obtain pages (and hence needs the original
520          * p2m entry).
521          */
522         kmap_flush_unused();
523
524         /*
525          * Setup the frame, update direct mapping, invalidate P2M,
526          * and add to balloon.
527          */
528         i = 0;
529         list_for_each_entry_safe(page, tmp, &pages, lru) {
530                 /* XENMEM_decrease_reservation requires a GFN */
531                 frame_list[i++] = xen_page_to_gfn(page);
532
533 #ifdef CONFIG_XEN_HAVE_PVMMU
534                 /*
535                  * We don't support PV MMU when Linux and Xen is using
536                  * different page granularity.
537                  */
538                 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
539
540                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
541                         unsigned long pfn = page_to_pfn(page);
542
543                         if (!PageHighMem(page)) {
544                                 ret = HYPERVISOR_update_va_mapping(
545                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
546                                                 __pte_ma(0), 0);
547                                 BUG_ON(ret);
548                         }
549                         __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
550                 }
551 #endif
552                 list_del(&page->lru);
553
554                 balloon_append(page);
555         }
556
557         flush_tlb_all();
558
559         set_xen_guest_handle(reservation.extent_start, frame_list);
560         reservation.nr_extents   = nr_pages;
561         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
562         BUG_ON(ret != nr_pages);
563
564         balloon_stats.current_pages -= nr_pages;
565
566         return state;
567 }
568
569 /*
570  * As this is a work item it is guaranteed to run as a single instance only.
571  * We may of course race updates of the target counts (which are protected
572  * by the balloon lock), or with changes to the Xen hard limit, but we will
573  * recover from these in time.
574  */
575 static void balloon_process(struct work_struct *work)
576 {
577         enum bp_state state = BP_DONE;
578         long credit;
579
580
581         do {
582                 mutex_lock(&balloon_mutex);
583
584                 credit = current_credit();
585
586                 if (credit > 0) {
587                         if (balloon_is_inflated())
588                                 state = increase_reservation(credit);
589                         else
590                                 state = reserve_additional_memory();
591                 }
592
593                 if (credit < 0)
594                         state = decrease_reservation(-credit, GFP_BALLOON);
595
596                 state = update_schedule(state);
597
598                 mutex_unlock(&balloon_mutex);
599
600                 cond_resched();
601
602         } while (credit && state == BP_DONE);
603
604         /* Schedule more work if there is some still to be done. */
605         if (state == BP_EAGAIN)
606                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
607 }
608
609 /* Resets the Xen limit, sets new target, and kicks off processing. */
610 void balloon_set_new_target(unsigned long target)
611 {
612         /* No need for lock. Not read-modify-write updates. */
613         balloon_stats.target_pages = target;
614         schedule_delayed_work(&balloon_worker, 0);
615 }
616 EXPORT_SYMBOL_GPL(balloon_set_new_target);
617
618 static int add_ballooned_pages(int nr_pages)
619 {
620         enum bp_state st;
621
622         if (xen_hotplug_unpopulated) {
623                 st = reserve_additional_memory();
624                 if (st != BP_ECANCELED) {
625                         mutex_unlock(&balloon_mutex);
626                         wait_event(balloon_wq,
627                                    !list_empty(&ballooned_pages));
628                         mutex_lock(&balloon_mutex);
629                         return 0;
630                 }
631         }
632
633         st = decrease_reservation(nr_pages, GFP_USER);
634         if (st != BP_DONE)
635                 return -ENOMEM;
636
637         return 0;
638 }
639
640 /**
641  * alloc_xenballooned_pages - get pages that have been ballooned out
642  * @nr_pages: Number of pages to get
643  * @pages: pages returned
644  * @return 0 on success, error otherwise
645  */
646 int alloc_xenballooned_pages(int nr_pages, struct page **pages)
647 {
648         int pgno = 0;
649         struct page *page;
650         int ret;
651
652         mutex_lock(&balloon_mutex);
653
654         balloon_stats.target_unpopulated += nr_pages;
655
656         while (pgno < nr_pages) {
657                 page = balloon_retrieve(true);
658                 if (page) {
659                         pages[pgno++] = page;
660 #ifdef CONFIG_XEN_HAVE_PVMMU
661                         /*
662                          * We don't support PV MMU when Linux and Xen is using
663                          * different page granularity.
664                          */
665                         BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
666
667                         ret = xen_alloc_p2m_entry(page_to_pfn(page));
668                         if (ret < 0)
669                                 goto out_undo;
670 #endif
671                 } else {
672                         ret = add_ballooned_pages(nr_pages - pgno);
673                         if (ret < 0)
674                                 goto out_undo;
675                 }
676         }
677         mutex_unlock(&balloon_mutex);
678         return 0;
679  out_undo:
680         mutex_unlock(&balloon_mutex);
681         free_xenballooned_pages(pgno, pages);
682         return ret;
683 }
684 EXPORT_SYMBOL(alloc_xenballooned_pages);
685
686 /**
687  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
688  * @nr_pages: Number of pages
689  * @pages: pages to return
690  */
691 void free_xenballooned_pages(int nr_pages, struct page **pages)
692 {
693         int i;
694
695         mutex_lock(&balloon_mutex);
696
697         for (i = 0; i < nr_pages; i++) {
698                 if (pages[i])
699                         balloon_append(pages[i]);
700         }
701
702         balloon_stats.target_unpopulated -= nr_pages;
703
704         /* The balloon may be too large now. Shrink it if needed. */
705         if (current_credit())
706                 schedule_delayed_work(&balloon_worker, 0);
707
708         mutex_unlock(&balloon_mutex);
709 }
710 EXPORT_SYMBOL(free_xenballooned_pages);
711
712 static void __init balloon_add_region(unsigned long start_pfn,
713                                       unsigned long pages)
714 {
715         unsigned long pfn, extra_pfn_end;
716         struct page *page;
717
718         /*
719          * If the amount of usable memory has been limited (e.g., with
720          * the 'mem' command line parameter), don't add pages beyond
721          * this limit.
722          */
723         extra_pfn_end = min(max_pfn, start_pfn + pages);
724
725         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
726                 page = pfn_to_page(pfn);
727                 /* totalram_pages and totalhigh_pages do not
728                    include the boot-time balloon extension, so
729                    don't subtract from it. */
730                 __balloon_append(page);
731         }
732
733         balloon_stats.total_pages += extra_pfn_end - start_pfn;
734 }
735
736 static int __init balloon_init(void)
737 {
738         int i;
739
740         if (!xen_domain())
741                 return -ENODEV;
742
743         pr_info("Initialising balloon driver\n");
744
745         balloon_stats.current_pages = xen_pv_domain()
746                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
747                 : get_num_physpages();
748         balloon_stats.target_pages  = balloon_stats.current_pages;
749         balloon_stats.balloon_low   = 0;
750         balloon_stats.balloon_high  = 0;
751         balloon_stats.total_pages   = balloon_stats.current_pages;
752
753         balloon_stats.schedule_delay = 1;
754         balloon_stats.max_schedule_delay = 32;
755         balloon_stats.retry_count = 1;
756         balloon_stats.max_retry_count = RETRY_UNLIMITED;
757
758 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
759         set_online_page_callback(&xen_online_page);
760         register_memory_notifier(&xen_memory_nb);
761         register_sysctl_table(xen_root);
762 #endif
763
764         /*
765          * Initialize the balloon with pages from the extra memory
766          * regions (see arch/x86/xen/setup.c).
767          */
768         for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
769                 if (xen_extra_mem[i].n_pfns)
770                         balloon_add_region(xen_extra_mem[i].start_pfn,
771                                            xen_extra_mem[i].n_pfns);
772
773         return 0;
774 }
775 subsys_initcall(balloon_init);