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/freezer.h>
 47#include <linux/kthread.h>
 48#include <linux/mm.h>
 49#include <linux/memblock.h>
 50#include <linux/pagemap.h>
 51#include <linux/highmem.h>
 52#include <linux/mutex.h>
 53#include <linux/list.h>
 54#include <linux/gfp.h>
 55#include <linux/notifier.h>
 56#include <linux/memory.h>
 57#include <linux/memory_hotplug.h>
 58#include <linux/percpu-defs.h>
 59#include <linux/slab.h>
 60#include <linux/sysctl.h>
 61#include <linux/moduleparam.h>
 62#include <linux/jiffies.h>
 63
 64#include <asm/page.h>
 65#include <asm/tlb.h>
 66
 67#include <asm/xen/hypervisor.h>
 68#include <asm/xen/hypercall.h>
 69
 70#include <xen/xen.h>
 71#include <xen/interface/xen.h>
 72#include <xen/interface/memory.h>
 73#include <xen/balloon.h>
 74#include <xen/features.h>
 75#include <xen/page.h>
 76#include <xen/mem-reservation.h>
 77
 78#undef MODULE_PARAM_PREFIX
 79#define MODULE_PARAM_PREFIX "xen."
 80
 81static uint __read_mostly balloon_boot_timeout = 180;
 82module_param(balloon_boot_timeout, uint, 0444);
 83
 84#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 85static int xen_hotplug_unpopulated;
 86
 87static const struct ctl_table balloon_table[] = {
 88	{
 89		.procname	= "hotplug_unpopulated",
 90		.data		= &xen_hotplug_unpopulated,
 91		.maxlen		= sizeof(int),
 92		.mode		= 0644,
 93		.proc_handler	= proc_dointvec_minmax,
 94		.extra1         = SYSCTL_ZERO,
 95		.extra2         = SYSCTL_ONE,
 96	},
 97};
 98
 99#else
100#define xen_hotplug_unpopulated 0
101#endif
102
103/*
104 * Use one extent per PAGE_SIZE to avoid to break down the page into
105 * multiple frame.
106 */
107#define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
108
109/*
110 * balloon_thread() state:
111 *
112 * BP_DONE: done or nothing to do,
113 * BP_WAIT: wait to be rescheduled,
114 * BP_EAGAIN: error, go to sleep,
115 * BP_ECANCELED: error, balloon operation canceled.
116 */
117
118static enum bp_state {
119	BP_DONE,
120	BP_WAIT,
121	BP_EAGAIN,
122	BP_ECANCELED
123} balloon_state = BP_DONE;
124
125/* Main waiting point for xen-balloon thread. */
126static DECLARE_WAIT_QUEUE_HEAD(balloon_thread_wq);
127
128static DEFINE_MUTEX(balloon_mutex);
129
130struct balloon_stats balloon_stats;
131EXPORT_SYMBOL_GPL(balloon_stats);
132
133/* We increase/decrease in batches which fit in a page */
134static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
135
136
137/* List of ballooned pages, threaded through the mem_map array. */
138static LIST_HEAD(ballooned_pages);
139static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
140
141/* When ballooning out (allocating memory to return to Xen) we don't really
142   want the kernel to try too hard since that can trigger the oom killer. */
143#define GFP_BALLOON \
144	(GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
145
146/* balloon_append: add the given page to the balloon. */
147static void balloon_append(struct page *page)
148{
149	if (!PageOffline(page))
150		__SetPageOffline(page);
151
152	/* Lowmem is re-populated first, so highmem pages go at list tail. */
153	if (PageHighMem(page)) {
154		list_add_tail(&page->lru, &ballooned_pages);
155		balloon_stats.balloon_high++;
156	} else {
157		list_add(&page->lru, &ballooned_pages);
158		balloon_stats.balloon_low++;
159	}
160	inc_node_page_state(page, NR_BALLOON_PAGES);
161
162	wake_up(&balloon_wq);
163}
164
165/* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
166static struct page *balloon_retrieve(bool require_lowmem)
167{
168	struct page *page;
169
170	if (list_empty(&ballooned_pages))
171		return NULL;
172
173	page = list_entry(ballooned_pages.next, struct page, lru);
174	if (require_lowmem && PageHighMem(page))
175		return NULL;
176	list_del(&page->lru);
177
178	if (PageHighMem(page))
179		balloon_stats.balloon_high--;
180	else
181		balloon_stats.balloon_low--;
182
183	__ClearPageOffline(page);
184	dec_node_page_state(page, NR_BALLOON_PAGES);
185
186	return page;
187}
188
189static struct page *balloon_next_page(struct page *page)
190{
191	struct list_head *next = page->lru.next;
192	if (next == &ballooned_pages)
193		return NULL;
194	return list_entry(next, struct page, lru);
195}
196
197static void update_schedule(void)
198{
199	if (balloon_state == BP_WAIT || balloon_state == BP_ECANCELED)
200		return;
201
202	if (balloon_state == BP_DONE) {
203		balloon_stats.schedule_delay = 1;
204		balloon_stats.retry_count = 1;
205		return;
206	}
207
208	++balloon_stats.retry_count;
209
210	if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
211			balloon_stats.retry_count > balloon_stats.max_retry_count) {
212		balloon_stats.schedule_delay = 1;
213		balloon_stats.retry_count = 1;
214		balloon_state = BP_ECANCELED;
215		return;
216	}
217
218	balloon_stats.schedule_delay <<= 1;
219
220	if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
221		balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
222
223	balloon_state = BP_EAGAIN;
224}
225
226#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
227static void release_memory_resource(struct resource *resource)
228{
229	if (!resource)
230		return;
231
232	/*
233	 * No need to reset region to identity mapped since we now
234	 * know that no I/O can be in this region
235	 */
236	release_resource(resource);
237	kfree(resource);
238}
239
240static struct resource *additional_memory_resource(phys_addr_t size)
241{
242	struct resource *res;
243	int ret;
244
245	res = kzalloc(sizeof(*res), GFP_KERNEL);
246	if (!res)
247		return NULL;
248
249	res->name = "System RAM";
250	res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
251
252	ret = allocate_resource(&iomem_resource, res,
253				size, 0, -1,
254				PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
255	if (ret < 0) {
256		pr_err("Cannot allocate new System RAM resource\n");
257		kfree(res);
258		return NULL;
259	}
260
261	return res;
262}
263
264static enum bp_state reserve_additional_memory(void)
265{
266	long credit;
267	struct resource *resource;
268	int nid, rc;
269	unsigned long balloon_hotplug;
270
271	credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
272		- balloon_stats.total_pages;
273
274	/*
275	 * Already hotplugged enough pages?  Wait for them to be
276	 * onlined.
277	 */
278	if (credit <= 0)
279		return BP_WAIT;
280
281	balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
282
283	resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
284	if (!resource)
285		goto err;
286
287	nid = memory_add_physaddr_to_nid(resource->start);
288
289#ifdef CONFIG_XEN_HAVE_PVMMU
290	/*
291	 * We don't support PV MMU when Linux and Xen is using
292	 * different page granularity.
293	 */
294	BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
295
296        /*
297         * add_memory() will build page tables for the new memory so
298         * the p2m must contain invalid entries so the correct
299         * non-present PTEs will be written.
300         *
301         * If a failure occurs, the original (identity) p2m entries
302         * are not restored since this region is now known not to
303         * conflict with any devices.
304         */ 
305	if (xen_pv_domain()) {
306		unsigned long pfn, i;
307
308		pfn = PFN_DOWN(resource->start);
309		for (i = 0; i < balloon_hotplug; i++) {
310			if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
311				pr_warn("set_phys_to_machine() failed, no memory added\n");
312				goto err;
313			}
314                }
315	}
316#endif
317
318	/*
319	 * add_memory_resource() will call online_pages() which in its turn
320	 * will call xen_online_page() callback causing deadlock if we don't
321	 * release balloon_mutex here. Unlocking here is safe because the
322	 * callers drop the mutex before trying again.
323	 */
324	mutex_unlock(&balloon_mutex);
325	/* add_memory_resource() requires the device_hotplug lock */
326	lock_device_hotplug();
327	rc = add_memory_resource(nid, resource, MHP_MERGE_RESOURCE);
328	unlock_device_hotplug();
329	mutex_lock(&balloon_mutex);
330
331	if (rc) {
332		pr_warn("Cannot add additional memory (%i)\n", rc);
333		goto err;
334	}
335
336	balloon_stats.total_pages += balloon_hotplug;
337
338	return BP_WAIT;
339  err:
340	release_memory_resource(resource);
341	return BP_ECANCELED;
342}
343
344static void xen_online_page(struct page *page, unsigned int order)
345{
346	unsigned long i, size = (1 << order);
347	unsigned long start_pfn = page_to_pfn(page);
348	struct page *p;
349
350	pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
351	mutex_lock(&balloon_mutex);
352	for (i = 0; i < size; i++) {
353		p = pfn_to_page(start_pfn + i);
354		balloon_append(p);
355	}
356	mutex_unlock(&balloon_mutex);
357}
358
359static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
360{
361	if (val == MEM_ONLINE)
362		wake_up(&balloon_thread_wq);
363
364	return NOTIFY_OK;
365}
366
367static struct notifier_block xen_memory_nb = {
368	.notifier_call = xen_memory_notifier,
369	.priority = 0
370};
371#else
372static enum bp_state reserve_additional_memory(void)
373{
374	balloon_stats.target_pages = balloon_stats.current_pages +
375				     balloon_stats.target_unpopulated;
376	return BP_ECANCELED;
377}
378#endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
379
380static long current_credit(void)
381{
382	return balloon_stats.target_pages - balloon_stats.current_pages;
383}
384
385static bool balloon_is_inflated(void)
386{
387	return balloon_stats.balloon_low || balloon_stats.balloon_high;
388}
389
390static enum bp_state increase_reservation(unsigned long nr_pages)
391{
392	int rc;
393	unsigned long i;
394	struct page   *page;
395
396	if (nr_pages > ARRAY_SIZE(frame_list))
397		nr_pages = ARRAY_SIZE(frame_list);
398
399	page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
400	for (i = 0; i < nr_pages; i++) {
401		if (!page) {
402			nr_pages = i;
403			break;
404		}
405
406		frame_list[i] = page_to_xen_pfn(page);
407		page = balloon_next_page(page);
408	}
409
410	rc = xenmem_reservation_increase(nr_pages, frame_list);
411	if (rc <= 0)
412		return BP_EAGAIN;
413
414	for (i = 0; i < rc; i++) {
415		page = balloon_retrieve(false);
416		BUG_ON(page == NULL);
417
418		xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
419
420		/*
421		 * Relinquish the page back to the allocator. Note that
422		 * some pages, including ones added via xen_online_page(), might
423		 * not be marked reserved; free_reserved_page() will handle that.
424		 */
425		free_reserved_page(page);
426	}
427
428	balloon_stats.current_pages += rc;
429
430	return BP_DONE;
431}
432
433static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
434{
435	enum bp_state state = BP_DONE;
436	unsigned long i;
437	struct page *page, *tmp;
438	int ret;
439	LIST_HEAD(pages);
440
441	if (nr_pages > ARRAY_SIZE(frame_list))
442		nr_pages = ARRAY_SIZE(frame_list);
443
444	for (i = 0; i < nr_pages; i++) {
445		page = alloc_page(gfp);
446		if (page == NULL) {
447			nr_pages = i;
448			state = BP_EAGAIN;
449			break;
450		}
451		adjust_managed_page_count(page, -1);
452		xenmem_reservation_scrub_page(page);
453		list_add(&page->lru, &pages);
454	}
455
456	/*
457	 * Ensure that ballooned highmem pages don't have kmaps.
458	 *
459	 * Do this before changing the p2m as kmap_flush_unused()
460	 * reads PTEs to obtain pages (and hence needs the original
461	 * p2m entry).
462	 */
463	kmap_flush_unused();
464
465	/*
466	 * Setup the frame, update direct mapping, invalidate P2M,
467	 * and add to balloon.
468	 */
469	i = 0;
470	list_for_each_entry_safe(page, tmp, &pages, lru) {
471		frame_list[i++] = xen_page_to_gfn(page);
472
473		xenmem_reservation_va_mapping_reset(1, &page);
474
475		list_del(&page->lru);
476
477		balloon_append(page);
478	}
479
480	flush_tlb_all();
481
482	ret = xenmem_reservation_decrease(nr_pages, frame_list);
483	BUG_ON(ret != nr_pages);
484
485	balloon_stats.current_pages -= nr_pages;
486
487	return state;
488}
489
490/*
491 * Stop waiting if either state is BP_DONE and ballooning action is
492 * needed, or if the credit has changed while state is not BP_DONE.
493 */
494static bool balloon_thread_cond(long credit)
495{
496	if (balloon_state == BP_DONE)
497		credit = 0;
498
499	return current_credit() != credit || kthread_should_stop();
500}
501
502/*
503 * As this is a kthread it is guaranteed to run as a single instance only.
504 * We may of course race updates of the target counts (which are protected
505 * by the balloon lock), or with changes to the Xen hard limit, but we will
506 * recover from these in time.
507 */
508static int balloon_thread(void *unused)
509{
510	long credit;
511	unsigned long timeout;
512
513	set_freezable();
514	for (;;) {
515		switch (balloon_state) {
516		case BP_DONE:
517		case BP_ECANCELED:
518			timeout = 3600 * HZ;
519			break;
520		case BP_EAGAIN:
521			timeout = balloon_stats.schedule_delay * HZ;
522			break;
523		case BP_WAIT:
524			timeout = HZ;
525			break;
526		}
527
528		credit = current_credit();
529
530		wait_event_freezable_timeout(balloon_thread_wq,
531			balloon_thread_cond(credit), timeout);
532
533		if (kthread_should_stop())
534			return 0;
535
536		mutex_lock(&balloon_mutex);
537
538		credit = current_credit();
539
540		if (credit > 0) {
541			if (balloon_is_inflated())
542				balloon_state = increase_reservation(credit);
543			else
544				balloon_state = reserve_additional_memory();
545		}
546
547		if (credit < 0) {
548			long n_pages;
549
550			n_pages = min(-credit, si_mem_available());
551			balloon_state = decrease_reservation(n_pages,
552							     GFP_BALLOON);
553			if (balloon_state == BP_DONE && n_pages != -credit &&
554			    n_pages < totalreserve_pages)
555				balloon_state = BP_EAGAIN;
556		}
557
558		update_schedule();
559
560		mutex_unlock(&balloon_mutex);
561
562		cond_resched();
563	}
564}
565
566/* Resets the Xen limit, sets new target, and kicks off processing. */
567void balloon_set_new_target(unsigned long target)
568{
569	/* No need for lock. Not read-modify-write updates. */
570	balloon_stats.target_pages = target;
571	wake_up(&balloon_thread_wq);
572}
573EXPORT_SYMBOL_GPL(balloon_set_new_target);
574
575static int add_ballooned_pages(unsigned int nr_pages)
576{
577	enum bp_state st;
578
579	if (xen_hotplug_unpopulated) {
580		st = reserve_additional_memory();
581		if (st != BP_ECANCELED) {
582			int rc;
583
584			mutex_unlock(&balloon_mutex);
585			rc = wait_event_interruptible(balloon_wq,
586				   !list_empty(&ballooned_pages));
587			mutex_lock(&balloon_mutex);
588			return rc ? -ENOMEM : 0;
589		}
590	}
591
592	if (si_mem_available() < nr_pages)
593		return -ENOMEM;
594
595	st = decrease_reservation(nr_pages, GFP_USER);
596	if (st != BP_DONE)
597		return -ENOMEM;
598
599	return 0;
600}
601
602/**
603 * xen_alloc_ballooned_pages - get pages that have been ballooned out
604 * @nr_pages: Number of pages to get
605 * @pages: pages returned
606 * @return 0 on success, error otherwise
607 */
608int xen_alloc_ballooned_pages(unsigned int nr_pages, struct page **pages)
609{
610	unsigned int pgno = 0;
611	struct page *page;
612	int ret;
613
614	mutex_lock(&balloon_mutex);
615
616	balloon_stats.target_unpopulated += nr_pages;
617
618	while (pgno < nr_pages) {
619		page = balloon_retrieve(true);
620		if (page) {
621			pages[pgno++] = page;
622#ifdef CONFIG_XEN_HAVE_PVMMU
623			/*
624			 * We don't support PV MMU when Linux and Xen is using
625			 * different page granularity.
626			 */
627			BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
628
629			if (xen_pv_domain()) {
630				ret = xen_alloc_p2m_entry(page_to_pfn(page));
631				if (ret < 0)
632					goto out_undo;
633			}
634#endif
635		} else {
636			ret = add_ballooned_pages(nr_pages - pgno);
637			if (ret < 0)
638				goto out_undo;
639		}
640	}
641	mutex_unlock(&balloon_mutex);
642	return 0;
643 out_undo:
644	mutex_unlock(&balloon_mutex);
645	xen_free_ballooned_pages(pgno, pages);
646	/*
647	 * NB: xen_free_ballooned_pages will only subtract pgno pages, but since
648	 * target_unpopulated is incremented with nr_pages at the start we need
649	 * to remove the remaining ones also, or accounting will be screwed.
650	 */
651	balloon_stats.target_unpopulated -= nr_pages - pgno;
652	return ret;
653}
654EXPORT_SYMBOL(xen_alloc_ballooned_pages);
655
656/**
657 * xen_free_ballooned_pages - return pages retrieved with get_ballooned_pages
658 * @nr_pages: Number of pages
659 * @pages: pages to return
660 */
661void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages)
662{
663	unsigned int i;
664
665	mutex_lock(&balloon_mutex);
666
667	for (i = 0; i < nr_pages; i++) {
668		if (pages[i])
669			balloon_append(pages[i]);
670	}
671
672	balloon_stats.target_unpopulated -= nr_pages;
673
674	/* The balloon may be too large now. Shrink it if needed. */
675	if (current_credit())
676		wake_up(&balloon_thread_wq);
677
678	mutex_unlock(&balloon_mutex);
679}
680EXPORT_SYMBOL(xen_free_ballooned_pages);
681
682static int __init balloon_add_regions(void)
683{
684	unsigned long start_pfn, pages;
685	unsigned long pfn, extra_pfn_end;
686	unsigned int i;
687
688	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
689		pages = xen_extra_mem[i].n_pfns;
690		if (!pages)
691			continue;
692
693		start_pfn = xen_extra_mem[i].start_pfn;
694
695		/*
696		 * If the amount of usable memory has been limited (e.g., with
697		 * the 'mem' command line parameter), don't add pages beyond
698		 * this limit.
699		 */
700		extra_pfn_end = min(max_pfn, start_pfn + pages);
701
702		for (pfn = start_pfn; pfn < extra_pfn_end; pfn++)
703			balloon_append(pfn_to_page(pfn));
704
705		/*
706		 * Extra regions are accounted for in the physmap, but need
707		 * decreasing from current_pages and target_pages to balloon
708		 * down the initial allocation, because they are already
709		 * accounted for in total_pages.
710		 */
711		pages = extra_pfn_end - start_pfn;
712		if (pages >= balloon_stats.current_pages ||
713		    pages >= balloon_stats.target_pages) {
714			WARN(1, "Extra pages underflow current target");
715			return -ERANGE;
716		}
717		balloon_stats.current_pages -= pages;
718		balloon_stats.target_pages -= pages;
719	}
720
721	return 0;
722}
723
724static int __init balloon_init(void)
725{
726	struct task_struct *task;
727	unsigned long current_pages;
728	int rc;
729
730	if (!xen_domain())
731		return -ENODEV;
732
733	pr_info("Initialising balloon driver\n");
734
735	if (xen_pv_domain()) {
736		if (xen_released_pages >= xen_start_info->nr_pages)
737			goto underflow;
738		current_pages = min(xen_start_info->nr_pages -
739		                    xen_released_pages, max_pfn);
740	} else {
741		if (xen_unpopulated_pages >= get_num_physpages())
742			goto underflow;
743		current_pages = get_num_physpages() - xen_unpopulated_pages;
744	}
745
746	balloon_stats.current_pages = current_pages;
747	balloon_stats.target_pages  = balloon_stats.current_pages;
748	balloon_stats.balloon_low   = 0;
749	balloon_stats.balloon_high  = 0;
750	balloon_stats.total_pages   = balloon_stats.current_pages;
751
752	balloon_stats.schedule_delay = 1;
753	balloon_stats.max_schedule_delay = 32;
754	balloon_stats.retry_count = 1;
755	balloon_stats.max_retry_count = 4;
756
757#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
758	set_online_page_callback(&xen_online_page);
759	register_memory_notifier(&xen_memory_nb);
760	register_sysctl_init("xen/balloon", balloon_table);
761#endif
762
763	rc = balloon_add_regions();
764	if (rc)
765		return rc;
766
767	task = kthread_run(balloon_thread, NULL, "xen-balloon");
768	if (IS_ERR(task)) {
769		pr_err("xen-balloon thread could not be started, ballooning will not work!\n");
770		return PTR_ERR(task);
771	}
772
773	/* Init the xen-balloon driver. */
774	xen_balloon_init();
775
776	return 0;
777
778 underflow:
779	WARN(1, "Released pages underflow current target");
780	return -ERANGE;
781}
782subsys_initcall(balloon_init);
783
784static int __init balloon_wait_finish(void)
785{
786	long credit, last_credit = 0;
787	unsigned long last_changed = 0;
788
789	if (!xen_domain())
790		return -ENODEV;
791
792	/* PV guests don't need to wait. */
793	if (xen_pv_domain() || !current_credit())
794		return 0;
795
796	pr_notice("Waiting for initial ballooning down having finished.\n");
797
798	while ((credit = current_credit()) < 0) {
799		if (credit != last_credit) {
800			last_changed = jiffies;
801			last_credit = credit;
802		}
803		if (balloon_state == BP_ECANCELED) {
804			pr_warn_once("Initial ballooning failed, %ld pages need to be freed.\n",
805				     -credit);
806			if (time_is_before_eq_jiffies(last_changed + HZ * balloon_boot_timeout))
807				panic("Initial ballooning failed!\n");
808		}
809
810		schedule_timeout_interruptible(HZ / 10);
811	}
812
813	pr_notice("Initial ballooning down finished.\n");
814
815	return 0;
816}
817late_initcall_sync(balloon_wait_finish);