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/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 #include <xen/mem-reservation.h>
75
76 static int xen_hotplug_unpopulated;
77
78 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
79
80 static struct ctl_table balloon_table[] = {
81 {
82 .procname = "hotplug_unpopulated",
83 .data = &xen_hotplug_unpopulated,
84 .maxlen = sizeof(int),
85 .mode = 0644,
86 .proc_handler = proc_dointvec_minmax,
87 .extra1 = SYSCTL_ZERO,
88 .extra2 = SYSCTL_ONE,
89 },
90 { }
91 };
92
93 static struct ctl_table balloon_root[] = {
94 {
95 .procname = "balloon",
96 .mode = 0555,
97 .child = balloon_table,
98 },
99 { }
100 };
101
102 static struct ctl_table xen_root[] = {
103 {
104 .procname = "xen",
105 .mode = 0555,
106 .child = balloon_root,
107 },
108 { }
109 };
110
111 #endif
112
113 /*
114 * Use one extent per PAGE_SIZE to avoid to break down the page into
115 * multiple frame.
116 */
117 #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
118
119 /*
120 * balloon_process() state:
121 *
122 * BP_DONE: done or nothing to do,
123 * BP_WAIT: wait to be rescheduled,
124 * BP_EAGAIN: error, go to sleep,
125 * BP_ECANCELED: error, balloon operation canceled.
126 */
127
128 enum bp_state {
129 BP_DONE,
130 BP_WAIT,
131 BP_EAGAIN,
132 BP_ECANCELED
133 };
134
135
136 static DEFINE_MUTEX(balloon_mutex);
137
138 struct balloon_stats balloon_stats;
139 EXPORT_SYMBOL_GPL(balloon_stats);
140
141 /* We increase/decrease in batches which fit in a page */
142 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
143
144
145 /* List of ballooned pages, threaded through the mem_map array. */
146 static LIST_HEAD(ballooned_pages);
147 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
148
149 /* Main work function, always executed in process context. */
150 static void balloon_process(struct work_struct *work);
151 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
152
153 /* When ballooning out (allocating memory to return to Xen) we don't really
154 want the kernel to try too hard since that can trigger the oom killer. */
155 #define GFP_BALLOON \
156 (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
157
158 /* balloon_append: add the given page to the balloon. */
balloon_append(struct page * page)159 static void balloon_append(struct page *page)
160 {
161 __SetPageOffline(page);
162
163 /* Lowmem is re-populated first, so highmem pages go at list tail. */
164 if (PageHighMem(page)) {
165 list_add_tail(&page->lru, &ballooned_pages);
166 balloon_stats.balloon_high++;
167 } else {
168 list_add(&page->lru, &ballooned_pages);
169 balloon_stats.balloon_low++;
170 }
171 wake_up(&balloon_wq);
172 }
173
174 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
balloon_retrieve(bool require_lowmem)175 static struct page *balloon_retrieve(bool require_lowmem)
176 {
177 struct page *page;
178
179 if (list_empty(&ballooned_pages))
180 return NULL;
181
182 page = list_entry(ballooned_pages.next, struct page, lru);
183 if (require_lowmem && PageHighMem(page))
184 return NULL;
185 list_del(&page->lru);
186
187 if (PageHighMem(page))
188 balloon_stats.balloon_high--;
189 else
190 balloon_stats.balloon_low--;
191
192 __ClearPageOffline(page);
193 return page;
194 }
195
balloon_next_page(struct page * page)196 static struct page *balloon_next_page(struct page *page)
197 {
198 struct list_head *next = page->lru.next;
199 if (next == &ballooned_pages)
200 return NULL;
201 return list_entry(next, struct page, lru);
202 }
203
update_schedule(enum bp_state state)204 static enum bp_state update_schedule(enum bp_state state)
205 {
206 if (state == BP_WAIT)
207 return BP_WAIT;
208
209 if (state == BP_ECANCELED)
210 return BP_ECANCELED;
211
212 if (state == BP_DONE) {
213 balloon_stats.schedule_delay = 1;
214 balloon_stats.retry_count = 1;
215 return BP_DONE;
216 }
217
218 ++balloon_stats.retry_count;
219
220 if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
221 balloon_stats.retry_count > balloon_stats.max_retry_count) {
222 balloon_stats.schedule_delay = 1;
223 balloon_stats.retry_count = 1;
224 return BP_ECANCELED;
225 }
226
227 balloon_stats.schedule_delay <<= 1;
228
229 if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
230 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
231
232 return BP_EAGAIN;
233 }
234
235 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
release_memory_resource(struct resource * resource)236 static void release_memory_resource(struct resource *resource)
237 {
238 if (!resource)
239 return;
240
241 /*
242 * No need to reset region to identity mapped since we now
243 * know that no I/O can be in this region
244 */
245 release_resource(resource);
246 kfree(resource);
247 }
248
additional_memory_resource(phys_addr_t size)249 static struct resource *additional_memory_resource(phys_addr_t size)
250 {
251 struct resource *res;
252 int ret;
253
254 res = kzalloc(sizeof(*res), GFP_KERNEL);
255 if (!res)
256 return NULL;
257
258 res->name = "System RAM";
259 res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
260
261 ret = allocate_resource(&iomem_resource, res,
262 size, 0, -1,
263 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
264 if (ret < 0) {
265 pr_err("Cannot allocate new System RAM resource\n");
266 kfree(res);
267 return NULL;
268 }
269
270 #ifdef CONFIG_SPARSEMEM
271 {
272 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
273 unsigned long pfn = res->start >> PAGE_SHIFT;
274
275 if (pfn > limit) {
276 pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n",
277 pfn, limit);
278 release_memory_resource(res);
279 return NULL;
280 }
281 }
282 #endif
283
284 return res;
285 }
286
reserve_additional_memory(void)287 static enum bp_state reserve_additional_memory(void)
288 {
289 long credit;
290 struct resource *resource;
291 int nid, rc;
292 unsigned long balloon_hotplug;
293
294 credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
295 - balloon_stats.total_pages;
296
297 /*
298 * Already hotplugged enough pages? Wait for them to be
299 * onlined.
300 */
301 if (credit <= 0)
302 return BP_WAIT;
303
304 balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
305
306 resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
307 if (!resource)
308 goto err;
309
310 nid = memory_add_physaddr_to_nid(resource->start);
311
312 #ifdef CONFIG_XEN_HAVE_PVMMU
313 /*
314 * We don't support PV MMU when Linux and Xen is using
315 * different page granularity.
316 */
317 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
318
319 /*
320 * add_memory() will build page tables for the new memory so
321 * the p2m must contain invalid entries so the correct
322 * non-present PTEs will be written.
323 *
324 * If a failure occurs, the original (identity) p2m entries
325 * are not restored since this region is now known not to
326 * conflict with any devices.
327 */
328 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
329 unsigned long pfn, i;
330
331 pfn = PFN_DOWN(resource->start);
332 for (i = 0; i < balloon_hotplug; i++) {
333 if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
334 pr_warn("set_phys_to_machine() failed, no memory added\n");
335 goto err;
336 }
337 }
338 }
339 #endif
340
341 /*
342 * add_memory_resource() will call online_pages() which in its turn
343 * will call xen_online_page() callback causing deadlock if we don't
344 * release balloon_mutex here. Unlocking here is safe because the
345 * callers drop the mutex before trying again.
346 */
347 mutex_unlock(&balloon_mutex);
348 /* add_memory_resource() requires the device_hotplug lock */
349 lock_device_hotplug();
350 rc = add_memory_resource(nid, resource);
351 unlock_device_hotplug();
352 mutex_lock(&balloon_mutex);
353
354 if (rc) {
355 pr_warn("Cannot add additional memory (%i)\n", rc);
356 goto err;
357 }
358
359 balloon_stats.total_pages += balloon_hotplug;
360
361 return BP_WAIT;
362 err:
363 release_memory_resource(resource);
364 return BP_ECANCELED;
365 }
366
xen_online_page(struct page * page,unsigned int order)367 static void xen_online_page(struct page *page, unsigned int order)
368 {
369 unsigned long i, size = (1 << order);
370 unsigned long start_pfn = page_to_pfn(page);
371 struct page *p;
372
373 pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
374 mutex_lock(&balloon_mutex);
375 for (i = 0; i < size; i++) {
376 p = pfn_to_page(start_pfn + i);
377 __online_page_set_limits(p);
378 balloon_append(p);
379 }
380 mutex_unlock(&balloon_mutex);
381 }
382
xen_memory_notifier(struct notifier_block * nb,unsigned long val,void * v)383 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
384 {
385 if (val == MEM_ONLINE)
386 schedule_delayed_work(&balloon_worker, 0);
387
388 return NOTIFY_OK;
389 }
390
391 static struct notifier_block xen_memory_nb = {
392 .notifier_call = xen_memory_notifier,
393 .priority = 0
394 };
395 #else
reserve_additional_memory(void)396 static enum bp_state reserve_additional_memory(void)
397 {
398 balloon_stats.target_pages = balloon_stats.current_pages +
399 balloon_stats.target_unpopulated;
400 return BP_ECANCELED;
401 }
402 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
403
current_credit(void)404 static long current_credit(void)
405 {
406 return balloon_stats.target_pages - balloon_stats.current_pages;
407 }
408
balloon_is_inflated(void)409 static bool balloon_is_inflated(void)
410 {
411 return balloon_stats.balloon_low || balloon_stats.balloon_high;
412 }
413
increase_reservation(unsigned long nr_pages)414 static enum bp_state increase_reservation(unsigned long nr_pages)
415 {
416 int rc;
417 unsigned long i;
418 struct page *page;
419
420 if (nr_pages > ARRAY_SIZE(frame_list))
421 nr_pages = ARRAY_SIZE(frame_list);
422
423 page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
424 for (i = 0; i < nr_pages; i++) {
425 if (!page) {
426 nr_pages = i;
427 break;
428 }
429
430 frame_list[i] = page_to_xen_pfn(page);
431 page = balloon_next_page(page);
432 }
433
434 rc = xenmem_reservation_increase(nr_pages, frame_list);
435 if (rc <= 0)
436 return BP_EAGAIN;
437
438 for (i = 0; i < rc; i++) {
439 page = balloon_retrieve(false);
440 BUG_ON(page == NULL);
441
442 xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
443
444 /* Relinquish the page back to the allocator. */
445 free_reserved_page(page);
446 }
447
448 balloon_stats.current_pages += rc;
449
450 return BP_DONE;
451 }
452
decrease_reservation(unsigned long nr_pages,gfp_t gfp)453 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
454 {
455 enum bp_state state = BP_DONE;
456 unsigned long i;
457 struct page *page, *tmp;
458 int ret;
459 LIST_HEAD(pages);
460
461 if (nr_pages > ARRAY_SIZE(frame_list))
462 nr_pages = ARRAY_SIZE(frame_list);
463
464 for (i = 0; i < nr_pages; i++) {
465 page = alloc_page(gfp);
466 if (page == NULL) {
467 nr_pages = i;
468 state = BP_EAGAIN;
469 break;
470 }
471 adjust_managed_page_count(page, -1);
472 xenmem_reservation_scrub_page(page);
473 list_add(&page->lru, &pages);
474 }
475
476 /*
477 * Ensure that ballooned highmem pages don't have kmaps.
478 *
479 * Do this before changing the p2m as kmap_flush_unused()
480 * reads PTEs to obtain pages (and hence needs the original
481 * p2m entry).
482 */
483 kmap_flush_unused();
484
485 /*
486 * Setup the frame, update direct mapping, invalidate P2M,
487 * and add to balloon.
488 */
489 i = 0;
490 list_for_each_entry_safe(page, tmp, &pages, lru) {
491 frame_list[i++] = xen_page_to_gfn(page);
492
493 xenmem_reservation_va_mapping_reset(1, &page);
494
495 list_del(&page->lru);
496
497 balloon_append(page);
498 }
499
500 flush_tlb_all();
501
502 ret = xenmem_reservation_decrease(nr_pages, frame_list);
503 BUG_ON(ret != nr_pages);
504
505 balloon_stats.current_pages -= nr_pages;
506
507 return state;
508 }
509
510 /*
511 * As this is a work item it is guaranteed to run as a single instance only.
512 * We may of course race updates of the target counts (which are protected
513 * by the balloon lock), or with changes to the Xen hard limit, but we will
514 * recover from these in time.
515 */
balloon_process(struct work_struct * work)516 static void balloon_process(struct work_struct *work)
517 {
518 enum bp_state state = BP_DONE;
519 long credit;
520
521
522 do {
523 mutex_lock(&balloon_mutex);
524
525 credit = current_credit();
526
527 if (credit > 0) {
528 if (balloon_is_inflated())
529 state = increase_reservation(credit);
530 else
531 state = reserve_additional_memory();
532 }
533
534 if (credit < 0) {
535 long n_pages;
536
537 n_pages = min(-credit, si_mem_available());
538 state = decrease_reservation(n_pages, GFP_BALLOON);
539 if (state == BP_DONE && n_pages != -credit &&
540 n_pages < totalreserve_pages)
541 state = BP_EAGAIN;
542 }
543
544 state = update_schedule(state);
545
546 mutex_unlock(&balloon_mutex);
547
548 cond_resched();
549
550 } while (credit && state == BP_DONE);
551
552 /* Schedule more work if there is some still to be done. */
553 if (state == BP_EAGAIN)
554 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
555 }
556
557 /* Resets the Xen limit, sets new target, and kicks off processing. */
balloon_set_new_target(unsigned long target)558 void balloon_set_new_target(unsigned long target)
559 {
560 /* No need for lock. Not read-modify-write updates. */
561 balloon_stats.target_pages = target;
562 schedule_delayed_work(&balloon_worker, 0);
563 }
564 EXPORT_SYMBOL_GPL(balloon_set_new_target);
565
add_ballooned_pages(int nr_pages)566 static int add_ballooned_pages(int nr_pages)
567 {
568 enum bp_state st;
569
570 if (xen_hotplug_unpopulated) {
571 st = reserve_additional_memory();
572 if (st != BP_ECANCELED) {
573 mutex_unlock(&balloon_mutex);
574 wait_event(balloon_wq,
575 !list_empty(&ballooned_pages));
576 mutex_lock(&balloon_mutex);
577 return 0;
578 }
579 }
580
581 if (si_mem_available() < nr_pages)
582 return -ENOMEM;
583
584 st = decrease_reservation(nr_pages, GFP_USER);
585 if (st != BP_DONE)
586 return -ENOMEM;
587
588 return 0;
589 }
590
591 /**
592 * alloc_xenballooned_pages - get pages that have been ballooned out
593 * @nr_pages: Number of pages to get
594 * @pages: pages returned
595 * @return 0 on success, error otherwise
596 */
alloc_xenballooned_pages(int nr_pages,struct page ** pages)597 int alloc_xenballooned_pages(int nr_pages, struct page **pages)
598 {
599 int pgno = 0;
600 struct page *page;
601 int ret;
602
603 mutex_lock(&balloon_mutex);
604
605 balloon_stats.target_unpopulated += nr_pages;
606
607 while (pgno < nr_pages) {
608 page = balloon_retrieve(true);
609 if (page) {
610 pages[pgno++] = page;
611 #ifdef CONFIG_XEN_HAVE_PVMMU
612 /*
613 * We don't support PV MMU when Linux and Xen is using
614 * different page granularity.
615 */
616 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
617
618 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
619 ret = xen_alloc_p2m_entry(page_to_pfn(page));
620 if (ret < 0)
621 goto out_undo;
622 }
623 #endif
624 } else {
625 ret = add_ballooned_pages(nr_pages - pgno);
626 if (ret < 0)
627 goto out_undo;
628 }
629 }
630 mutex_unlock(&balloon_mutex);
631 return 0;
632 out_undo:
633 mutex_unlock(&balloon_mutex);
634 free_xenballooned_pages(pgno, pages);
635 return ret;
636 }
637 EXPORT_SYMBOL(alloc_xenballooned_pages);
638
639 /**
640 * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
641 * @nr_pages: Number of pages
642 * @pages: pages to return
643 */
free_xenballooned_pages(int nr_pages,struct page ** pages)644 void free_xenballooned_pages(int nr_pages, struct page **pages)
645 {
646 int i;
647
648 mutex_lock(&balloon_mutex);
649
650 for (i = 0; i < nr_pages; i++) {
651 if (pages[i])
652 balloon_append(pages[i]);
653 }
654
655 balloon_stats.target_unpopulated -= nr_pages;
656
657 /* The balloon may be too large now. Shrink it if needed. */
658 if (current_credit())
659 schedule_delayed_work(&balloon_worker, 0);
660
661 mutex_unlock(&balloon_mutex);
662 }
663 EXPORT_SYMBOL(free_xenballooned_pages);
664
665 #ifdef CONFIG_XEN_PV
balloon_add_region(unsigned long start_pfn,unsigned long pages)666 static void __init balloon_add_region(unsigned long start_pfn,
667 unsigned long pages)
668 {
669 unsigned long pfn, extra_pfn_end;
670
671 /*
672 * If the amount of usable memory has been limited (e.g., with
673 * the 'mem' command line parameter), don't add pages beyond
674 * this limit.
675 */
676 extra_pfn_end = min(max_pfn, start_pfn + pages);
677
678 for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
679 /* totalram_pages and totalhigh_pages do not
680 include the boot-time balloon extension, so
681 don't subtract from it. */
682 balloon_append(pfn_to_page(pfn));
683 }
684
685 balloon_stats.total_pages += extra_pfn_end - start_pfn;
686 }
687 #endif
688
balloon_init(void)689 static int __init balloon_init(void)
690 {
691 if (!xen_domain())
692 return -ENODEV;
693
694 pr_info("Initialising balloon driver\n");
695
696 #ifdef CONFIG_XEN_PV
697 balloon_stats.current_pages = xen_pv_domain()
698 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
699 : get_num_physpages();
700 #else
701 balloon_stats.current_pages = get_num_physpages();
702 #endif
703 balloon_stats.target_pages = balloon_stats.current_pages;
704 balloon_stats.balloon_low = 0;
705 balloon_stats.balloon_high = 0;
706 balloon_stats.total_pages = balloon_stats.current_pages;
707
708 balloon_stats.schedule_delay = 1;
709 balloon_stats.max_schedule_delay = 32;
710 balloon_stats.retry_count = 1;
711 balloon_stats.max_retry_count = 4;
712
713 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
714 set_online_page_callback(&xen_online_page);
715 register_memory_notifier(&xen_memory_nb);
716 register_sysctl_table(xen_root);
717 #endif
718
719 #ifdef CONFIG_XEN_PV
720 {
721 int i;
722
723 /*
724 * Initialize the balloon with pages from the extra memory
725 * regions (see arch/x86/xen/setup.c).
726 */
727 for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
728 if (xen_extra_mem[i].n_pfns)
729 balloon_add_region(xen_extra_mem[i].start_pfn,
730 xen_extra_mem[i].n_pfns);
731 }
732 #endif
733
734 /* Init the xen-balloon driver. */
735 xen_balloon_init();
736
737 return 0;
738 }
739 subsys_initcall(balloon_init);
740