drivers/virtio/virtio_balloon.c - kernel/msm-4.9 - Gitiles

 /*
  * Virtio balloon implementation, inspired by Dor Laor and Marcelo
  * Tosatti's implementations.
  *
  *  Copyright 2008 Rusty Russell IBM Corporation
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */

 #include <linux/virtio.h>
 #include <linux/virtio_balloon.h>
 #include <linux/swap.h>
 #include <linux/workqueue.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/balloon_compaction.h>
 #include <linux/oom.h>
 #include <linux/wait.h>
 #include <linux/mm.h>

 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
  * multiple balloon pages.  All memory counters in this driver are in balloon
  * page units.
  */
 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
 #define OOM_VBALLOON_DEFAULT_PAGES 256
 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80

 static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
 module_param(oom_pages, int, S_IRUSR | S_IWUSR);
 MODULE_PARM_DESC(oom_pages, "pages to free on OOM");

 struct virtio_balloon {
 	struct virtio_device *vdev;
 	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;

 	/* The balloon servicing is delegated to a freezable workqueue. */
 	struct work_struct update_balloon_stats_work;
 	struct work_struct update_balloon_size_work;

 	/* Prevent updating balloon when it is being canceled. */
 	spinlock_t stop_update_lock;
 	bool stop_update;

 	/* Waiting for host to ack the pages we released. */
 	wait_queue_head_t acked;

 	/* Number of balloon pages we've told the Host we're not using. */
 	unsigned int num_pages;
 	/*
 	 * The pages we've told the Host we're not using are enqueued
 	 * at vb_dev_info->pages list.
 	 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
 	 * to num_pages above.
 	 */
 	struct balloon_dev_info vb_dev_info;

 	/* Synchronize access/update to this struct virtio_balloon elements */
 	struct mutex balloon_lock;

 	/* The array of pfns we tell the Host about. */
 	unsigned int num_pfns;
 	u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];

 	/* Memory statistics */
 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];

 	/* To register callback in oom notifier call chain */
 	struct notifier_block nb;
 };

 static struct virtio_device_id id_table[] = {
 	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
 	{ 0 },
 };

 static u32 page_to_balloon_pfn(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);

 	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
 	/* Convert pfn from Linux page size to balloon page size. */
 	return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 }

 static struct page *balloon_pfn_to_page(u32 pfn)
 {
 	BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
 	return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
 }

 static void balloon_ack(struct virtqueue *vq)
 {
 	struct virtio_balloon *vb = vq->vdev->priv;

 	wake_up(&vb->acked);
 }

 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 {
 	struct scatterlist sg;
 	unsigned int len;

 	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);

 	/* We should always be able to add one buffer to an empty queue. */
 	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 	virtqueue_kick(vq);

 	/* When host has read buffer, this completes via balloon_ack */
 	wait_event(vb->acked, virtqueue_get_buf(vq, &len));

 }

 static void set_page_pfns(u32 pfns[], struct page *page)
 {
 	unsigned int i;

 	/* Set balloon pfns pointing at this page.
 	 * Note that the first pfn points at start of the page. */
 	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 		pfns[i] = page_to_balloon_pfn(page) + i;
 }

 static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
 {
 	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
 	unsigned num_allocated_pages;

 	/* We can only do one array worth at a time. */
 	num = min(num, ARRAY_SIZE(vb->pfns));

 	mutex_lock(&vb->balloon_lock);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		struct page *page = balloon_page_enqueue(vb_dev_info);

 		if (!page) {
 			dev_info_ratelimited(&vb->vdev->dev,
 					     "Out of puff! Can't get %u pages\n",
 					     VIRTIO_BALLOON_PAGES_PER_PAGE);
 			/* Sleep for at least 1/5 of a second before retry. */
 			msleep(200);
 			break;
 		}
 		set_page_pfns(vb->pfns + vb->num_pfns, page);
 		vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 		if (!virtio_has_feature(vb->vdev,
 					VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 			adjust_managed_page_count(page, -1);
 	}

 	num_allocated_pages = vb->num_pfns;
 	/* Did we get any? */
 	if (vb->num_pfns != 0)
 		tell_host(vb, vb->inflate_vq);
 	mutex_unlock(&vb->balloon_lock);

 	return num_allocated_pages;
 }

 static void release_pages_balloon(struct virtio_balloon *vb)
 {
 	unsigned int i;

 	/* Find pfns pointing at start of each page, get pages and free them. */
 	for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		struct page *page = balloon_pfn_to_page(vb->pfns[i]);
 		if (!virtio_has_feature(vb->vdev,
 					VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 			adjust_managed_page_count(page, 1);
 		put_page(page); /* balloon reference */
 	}
 }

 static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
 {
 	unsigned num_freed_pages;
 	struct page *page;
 	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;

 	/* We can only do one array worth at a time. */
 	num = min(num, ARRAY_SIZE(vb->pfns));

 	mutex_lock(&vb->balloon_lock);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		page = balloon_page_dequeue(vb_dev_info);
 		if (!page)
 			break;
 		set_page_pfns(vb->pfns + vb->num_pfns, page);
 		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 	}

 	num_freed_pages = vb->num_pfns;
 	/*
 	 * Note that if
 	 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 	 * is true, we *have* to do it in this order
 	 */
 	if (vb->num_pfns != 0)
 		tell_host(vb, vb->deflate_vq);
 	release_pages_balloon(vb);
 	mutex_unlock(&vb->balloon_lock);
 	return num_freed_pages;
 }

 static inline void update_stat(struct virtio_balloon *vb, int idx,
 			       u16 tag, u64 val)
 {
 	BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 	vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
 	vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
 }

 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)

 static void update_balloon_stats(struct virtio_balloon *vb)
 {
 	unsigned long events[NR_VM_EVENT_ITEMS];
 	struct sysinfo i;
 	int idx = 0;
 	long available;

 	all_vm_events(events);
 	si_meminfo(&i);

 	available = si_mem_available();

 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 				pages_to_bytes(events[PSWPIN]));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 				pages_to_bytes(events[PSWPOUT]));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 				pages_to_bytes(i.freeram));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 				pages_to_bytes(i.totalram));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
 				pages_to_bytes(available));
 }

 /*
  * While most virtqueues communicate guest-initiated requests to the hypervisor,
  * the stats queue operates in reverse.  The driver initializes the virtqueue
  * with a single buffer.  From that point forward, all conversations consist of
  * a hypervisor request (a call to this function) which directs us to refill
  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
  * we delegate the job to a freezable workqueue that will do the actual work via
  * stats_handle_request().
  */
 static void stats_request(struct virtqueue *vq)
 {
 	struct virtio_balloon *vb = vq->vdev->priv;

 	spin_lock(&vb->stop_update_lock);
 	if (!vb->stop_update)
 		queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
 	spin_unlock(&vb->stop_update_lock);
 }

 static void stats_handle_request(struct virtio_balloon *vb)
 {
 	struct virtqueue *vq;
 	struct scatterlist sg;
 	unsigned int len;

 	update_balloon_stats(vb);

 	vq = vb->stats_vq;
 	if (!virtqueue_get_buf(vq, &len))
 		return;
 	sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 	virtqueue_kick(vq);
 }

 static void virtballoon_changed(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;
 	unsigned long flags;

 	spin_lock_irqsave(&vb->stop_update_lock, flags);
 	if (!vb->stop_update)
 		queue_work(system_freezable_wq, &vb->update_balloon_size_work);
 	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
 }

 static inline s64 towards_target(struct virtio_balloon *vb)
 {
 	s64 target;
 	u32 num_pages;

 	virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
 		     &num_pages);

 	/* Legacy balloon config space is LE, unlike all other devices. */
 	if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 		num_pages = le32_to_cpu((__force __le32)num_pages);

 	target = num_pages;
 	return target - vb->num_pages;
 }

 static void update_balloon_size(struct virtio_balloon *vb)
 {
 	u32 actual = vb->num_pages;

 	/* Legacy balloon config space is LE, unlike all other devices. */
 	if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 		actual = (__force u32)cpu_to_le32(actual);

 	virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
 		      &actual);
 }

 /*
  * virtballoon_oom_notify - release pages when system is under severe
  *			    memory pressure (called from out_of_memory())
  * @self : notifier block struct
  * @dummy: not used
  * @parm : returned - number of freed pages
  *
  * The balancing of memory by use of the virtio balloon should not cause
  * the termination of processes while there are pages in the balloon.
  * If virtio balloon manages to release some memory, it will make the
  * system return and retry the allocation that forced the OOM killer
  * to run.
  */
 static int virtballoon_oom_notify(struct notifier_block *self,
 				  unsigned long dummy, void *parm)
 {
 	struct virtio_balloon *vb;
 	unsigned long *freed;
 	unsigned num_freed_pages;

 	vb = container_of(self, struct virtio_balloon, nb);
 	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 		return NOTIFY_OK;

 	freed = parm;
 	num_freed_pages = leak_balloon(vb, oom_pages);
 	update_balloon_size(vb);
 	*freed += num_freed_pages;

 	return NOTIFY_OK;
 }

 static void update_balloon_stats_func(struct work_struct *work)
 {
 	struct virtio_balloon *vb;

 	vb = container_of(work, struct virtio_balloon,
 			  update_balloon_stats_work);
 	stats_handle_request(vb);
 }

 static void update_balloon_size_func(struct work_struct *work)
 {
 	struct virtio_balloon *vb;
 	s64 diff;

 	vb = container_of(work, struct virtio_balloon,
 			  update_balloon_size_work);
 	diff = towards_target(vb);

 	if (diff > 0)
 		diff -= fill_balloon(vb, diff);
 	else if (diff < 0)
 		diff += leak_balloon(vb, -diff);
 	update_balloon_size(vb);

 	if (diff)
 		queue_work(system_freezable_wq, work);
 }

 static int init_vqs(struct virtio_balloon *vb)
 {
 	struct virtqueue *vqs[3];
 	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 	static const char * const names[] = { "inflate", "deflate", "stats" };
 	int err, nvqs;

 	/*
 	 * We expect two virtqueues: inflate and deflate, and
 	 * optionally stat.
 	 */
 	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 	err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
 	if (err)
 		return err;

 	vb->inflate_vq = vqs[0];
 	vb->deflate_vq = vqs[1];
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 		struct scatterlist sg;
 		vb->stats_vq = vqs[2];

 		/*
 		 * Prime this virtqueue with one buffer so the hypervisor can
 		 * use it to signal us later (it can't be broken yet!).
 		 */
 		sg_init_one(&sg, vb->stats, sizeof vb->stats);
 		if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
 		    < 0)
 			BUG();
 		virtqueue_kick(vb->stats_vq);
 	}
 	return 0;
 }

 #ifdef CONFIG_BALLOON_COMPACTION
 /*
  * virtballoon_migratepage - perform the balloon page migration on behalf of
  *			     a compation thread.     (called under page lock)
  * @vb_dev_info: the balloon device
  * @newpage: page that will replace the isolated page after migration finishes.
  * @page   : the isolated (old) page that is about to be migrated to newpage.
  * @mode   : compaction mode -- not used for balloon page migration.
  *
  * After a ballooned page gets isolated by compaction procedures, this is the
  * function that performs the page migration on behalf of a compaction thread
  * The page migration for virtio balloon is done in a simple swap fashion which
  * follows these two macro steps:
  *  1) insert newpage into vb->pages list and update the host about it;
  *  2) update the host about the old page removed from vb->pages list;
  *
  * This function preforms the balloon page migration task.
  * Called through balloon_mapping->a_ops->migratepage
  */
 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 		struct page *newpage, struct page *page, enum migrate_mode mode)
 {
 	struct virtio_balloon *vb = container_of(vb_dev_info,
 			struct virtio_balloon, vb_dev_info);
 	unsigned long flags;

 	/*
 	 * In order to avoid lock contention while migrating pages concurrently
 	 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
 	 * this turn, as it is easier to retry the page migration later.
 	 * This also prevents fill_balloon() getting stuck into a mutex
 	 * recursion in the case it ends up triggering memory compaction
 	 * while it is attempting to inflate the ballon.
 	 */
 	if (!mutex_trylock(&vb->balloon_lock))
 		return -EAGAIN;

 	get_page(newpage); /* balloon reference */

 	/* balloon's page migration 1st step  -- inflate "newpage" */
 	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 	balloon_page_insert(vb_dev_info, newpage);
 	vb_dev_info->isolated_pages--;
 	__count_vm_event(BALLOON_MIGRATE);
 	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 	set_page_pfns(vb->pfns, newpage);
 	tell_host(vb, vb->inflate_vq);

 	/* balloon's page migration 2nd step -- deflate "page" */
 	balloon_page_delete(page);
 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 	set_page_pfns(vb->pfns, page);
 	tell_host(vb, vb->deflate_vq);

 	mutex_unlock(&vb->balloon_lock);

 	put_page(page); /* balloon reference */

 	return MIGRATEPAGE_SUCCESS;
 }
 #endif /* CONFIG_BALLOON_COMPACTION */

 static int virtballoon_probe(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb;
 	int err;

 	if (!vdev->config->get) {
 		dev_err(&vdev->dev, "%s failure: config access disabled\n",
 			__func__);
 		return -EINVAL;
 	}

 	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 	if (!vb) {
 		err = -ENOMEM;
 		goto out;
 	}

 	INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
 	INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
 	spin_lock_init(&vb->stop_update_lock);
 	vb->stop_update = false;
 	vb->num_pages = 0;
 	mutex_init(&vb->balloon_lock);
 	init_waitqueue_head(&vb->acked);
 	vb->vdev = vdev;

 	balloon_devinfo_init(&vb->vb_dev_info);
 #ifdef CONFIG_BALLOON_COMPACTION
 	vb->vb_dev_info.migratepage = virtballoon_migratepage;
 #endif

 	err = init_vqs(vb);
 	if (err)
 		goto out_free_vb;

 	vb->nb.notifier_call = virtballoon_oom_notify;
 	vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
 	err = register_oom_notifier(&vb->nb);
 	if (err < 0)
 		goto out_oom_notify;

 	virtio_device_ready(vdev);

 	return 0;

 out_oom_notify:
 	vdev->config->del_vqs(vdev);
 out_free_vb:
 	kfree(vb);
 out:
 	return err;
 }

 static void remove_common(struct virtio_balloon *vb)
 {
 	/* There might be pages left in the balloon: free them. */
 	while (vb->num_pages)
 		leak_balloon(vb, vb->num_pages);
 	update_balloon_size(vb);

 	/* Now we reset the device so we can clean up the queues. */
 	vb->vdev->config->reset(vb->vdev);

 	vb->vdev->config->del_vqs(vb->vdev);
 }

 static void virtballoon_remove(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;

 	unregister_oom_notifier(&vb->nb);

 	spin_lock_irq(&vb->stop_update_lock);
 	vb->stop_update = true;
 	spin_unlock_irq(&vb->stop_update_lock);
 	cancel_work_sync(&vb->update_balloon_size_work);
 	cancel_work_sync(&vb->update_balloon_stats_work);

 	remove_common(vb);
 	kfree(vb);
 }

 #ifdef CONFIG_PM_SLEEP
 static int virtballoon_freeze(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;

 	/*
 	 * The workqueue is already frozen by the PM core before this
 	 * function is called.
 	 */
 	remove_common(vb);
 	return 0;
 }

 static int virtballoon_restore(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;
 	int ret;

 	ret = init_vqs(vdev->priv);
 	if (ret)
 		return ret;

 	virtio_device_ready(vdev);

 	if (towards_target(vb))
 		virtballoon_changed(vdev);
 	update_balloon_size(vb);
 	return 0;
 }
 #endif

 static unsigned int features[] = {
 	VIRTIO_BALLOON_F_MUST_TELL_HOST,
 	VIRTIO_BALLOON_F_STATS_VQ,
 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
 };

 static struct virtio_driver virtio_balloon_driver = {
 	.feature_table = features,
 	.feature_table_size = ARRAY_SIZE(features),
 	.driver.name =	KBUILD_MODNAME,
 	.driver.owner =	THIS_MODULE,
 	.id_table =	id_table,
 	.probe =	virtballoon_probe,
 	.remove =	virtballoon_remove,
 	.config_changed = virtballoon_changed,
 #ifdef CONFIG_PM_SLEEP
 	.freeze	=	virtballoon_freeze,
 	.restore =	virtballoon_restore,
 #endif
 };

 module_virtio_driver(virtio_balloon_driver);
 MODULE_DEVICE_TABLE(virtio, id_table);
 MODULE_DESCRIPTION("Virtio balloon driver");
 MODULE_LICENSE("GPL");
	/*
	* Virtio balloon implementation, inspired by Dor Laor and Marcelo
	* Tosatti's implementations.
	*
	* Copyright 2008 Rusty Russell IBM Corporation
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	*/

	#include <linux/virtio.h>
	#include <linux/virtio_balloon.h>
	#include <linux/swap.h>
	#include <linux/workqueue.h>
	#include <linux/delay.h>
	#include <linux/slab.h>
	#include <linux/module.h>
	#include <linux/balloon_compaction.h>
	#include <linux/oom.h>
	#include <linux/wait.h>
	#include <linux/mm.h>

	/*
	* Balloon device works in 4K page units. So each page is pointed to by
	* multiple balloon pages. All memory counters in this driver are in balloon
	* page units.
	*/
	#define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
	#define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
	#define OOM_VBALLOON_DEFAULT_PAGES 256
	#define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80

	static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
	module_param(oom_pages, int, S_IRUSR \| S_IWUSR);
	MODULE_PARM_DESC(oom_pages, "pages to free on OOM");

	struct virtio_balloon {
	struct virtio_device *vdev;
	struct virtqueue inflate_vq, deflate_vq, *stats_vq;

	/* The balloon servicing is delegated to a freezable workqueue. */
	struct work_struct update_balloon_stats_work;
	struct work_struct update_balloon_size_work;

	/* Prevent updating balloon when it is being canceled. */
	spinlock_t stop_update_lock;
	bool stop_update;

	/* Waiting for host to ack the pages we released. */
	wait_queue_head_t acked;

	/* Number of balloon pages we've told the Host we're not using. */
	unsigned int num_pages;
	/*
	* The pages we've told the Host we're not using are enqueued
	* at vb_dev_info->pages list.
	* Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
	* to num_pages above.
	*/
	struct balloon_dev_info vb_dev_info;

	/* Synchronize access/update to this struct virtio_balloon elements */
	struct mutex balloon_lock;

	/* The array of pfns we tell the Host about. */
	unsigned int num_pfns;
	u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];

	/* Memory statistics */
	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];

	/* To register callback in oom notifier call chain */
	struct notifier_block nb;
	};

	static struct virtio_device_id id_table[] = {
	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
	{ 0 },
	};

	static u32 page_to_balloon_pfn(struct page *page)
	{
	unsigned long pfn = page_to_pfn(page);

	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
	/* Convert pfn from Linux page size to balloon page size. */
	return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
	}

	static struct page *balloon_pfn_to_page(u32 pfn)
	{
	BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
	return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
	}

	static void balloon_ack(struct virtqueue *vq)
	{
	struct virtio_balloon *vb = vq->vdev->priv;

	wake_up(&vb->acked);
	}

	static void tell_host(struct virtio_balloon vb, struct virtqueue vq)
	{
	struct scatterlist sg;
	unsigned int len;

	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);

	/* We should always be able to add one buffer to an empty queue. */
	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
	virtqueue_kick(vq);

	/* When host has read buffer, this completes via balloon_ack */
	wait_event(vb->acked, virtqueue_get_buf(vq, &len));

	}

	static void set_page_pfns(u32 pfns[], struct page *page)
	{
	unsigned int i;

	/* Set balloon pfns pointing at this page.
	* Note that the first pfn points at start of the page. */
	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
	pfns[i] = page_to_balloon_pfn(page) + i;
	}

	static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
	{
	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
	unsigned num_allocated_pages;

	/* We can only do one array worth at a time. */
	num = min(num, ARRAY_SIZE(vb->pfns));

	mutex_lock(&vb->balloon_lock);
	for (vb->num_pfns = 0; vb->num_pfns < num;
	vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
	struct page *page = balloon_page_enqueue(vb_dev_info);

	if (!page) {
	dev_info_ratelimited(&vb->vdev->dev,
	"Out of puff! Can't get %u pages\n",
	VIRTIO_BALLOON_PAGES_PER_PAGE);
	/* Sleep for at least 1/5 of a second before retry. */
	msleep(200);
	break;
	}
	set_page_pfns(vb->pfns + vb->num_pfns, page);
	vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
	if (!virtio_has_feature(vb->vdev,
	VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
	adjust_managed_page_count(page, -1);
	}

	num_allocated_pages = vb->num_pfns;
	/* Did we get any? */
	if (vb->num_pfns != 0)
	tell_host(vb, vb->inflate_vq);
	mutex_unlock(&vb->balloon_lock);

	return num_allocated_pages;
	}

	static void release_pages_balloon(struct virtio_balloon *vb)
	{
	unsigned int i;

	/* Find pfns pointing at start of each page, get pages and free them. */
	for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
	struct page *page = balloon_pfn_to_page(vb->pfns[i]);
	if (!virtio_has_feature(vb->vdev,
	VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
	adjust_managed_page_count(page, 1);
	put_page(page); /* balloon reference */
	}
	}

	static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
	{
	unsigned num_freed_pages;
	struct page *page;
	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;

	/* We can only do one array worth at a time. */
	num = min(num, ARRAY_SIZE(vb->pfns));

	mutex_lock(&vb->balloon_lock);
	for (vb->num_pfns = 0; vb->num_pfns < num;
	vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
	page = balloon_page_dequeue(vb_dev_info);
	if (!page)
	break;
	set_page_pfns(vb->pfns + vb->num_pfns, page);
	vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
	}

	num_freed_pages = vb->num_pfns;
	/*
	* Note that if
	* virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
	* is true, we have to do it in this order
	*/
	if (vb->num_pfns != 0)
	tell_host(vb, vb->deflate_vq);
	release_pages_balloon(vb);
	mutex_unlock(&vb->balloon_lock);
	return num_freed_pages;
	}

	static inline void update_stat(struct virtio_balloon *vb, int idx,
	u16 tag, u64 val)
	{
	BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
	vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
	vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
	}

	#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)

	static void update_balloon_stats(struct virtio_balloon *vb)
	{
	unsigned long events[NR_VM_EVENT_ITEMS];
	struct sysinfo i;
	int idx = 0;
	long available;

	all_vm_events(events);
	si_meminfo(&i);

	available = si_mem_available();

	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
	pages_to_bytes(events[PSWPIN]));
	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
	pages_to_bytes(events[PSWPOUT]));
	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
	pages_to_bytes(i.freeram));
	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
	pages_to_bytes(i.totalram));
	update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
	pages_to_bytes(available));
	}

	/*
	* While most virtqueues communicate guest-initiated requests to the hypervisor,
	* the stats queue operates in reverse. The driver initializes the virtqueue
	* with a single buffer. From that point forward, all conversations consist of
	* a hypervisor request (a call to this function) which directs us to refill
	* the virtqueue with a fresh stats buffer. Since stats collection can sleep,
	* we delegate the job to a freezable workqueue that will do the actual work via
	* stats_handle_request().
	*/
	static void stats_request(struct virtqueue *vq)
	{
	struct virtio_balloon *vb = vq->vdev->priv;

	spin_lock(&vb->stop_update_lock);
	if (!vb->stop_update)
	queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
	spin_unlock(&vb->stop_update_lock);
	}

	static void stats_handle_request(struct virtio_balloon *vb)
	{
	struct virtqueue *vq;
	struct scatterlist sg;
	unsigned int len;

	update_balloon_stats(vb);

	vq = vb->stats_vq;
	if (!virtqueue_get_buf(vq, &len))
	return;
	sg_init_one(&sg, vb->stats, sizeof(vb->stats));
	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
	virtqueue_kick(vq);
	}

	static void virtballoon_changed(struct virtio_device *vdev)
	{
	struct virtio_balloon *vb = vdev->priv;
	unsigned long flags;

	spin_lock_irqsave(&vb->stop_update_lock, flags);
	if (!vb->stop_update)
	queue_work(system_freezable_wq, &vb->update_balloon_size_work);
	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
	}

	static inline s64 towards_target(struct virtio_balloon *vb)
	{
	s64 target;
	u32 num_pages;

	virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
	&num_pages);

	/* Legacy balloon config space is LE, unlike all other devices. */
	if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
	num_pages = le32_to_cpu((__force __le32)num_pages);

	target = num_pages;
	return target - vb->num_pages;
	}

	static void update_balloon_size(struct virtio_balloon *vb)
	{
	u32 actual = vb->num_pages;

	/* Legacy balloon config space is LE, unlike all other devices. */
	if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
	actual = (__force u32)cpu_to_le32(actual);

	virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
	&actual);
	}

	/*
	* virtballoon_oom_notify - release pages when system is under severe
	* memory pressure (called from out_of_memory())
	* @self : notifier block struct
	* @dummy: not used
	* @parm : returned - number of freed pages
	*
	* The balancing of memory by use of the virtio balloon should not cause
	* the termination of processes while there are pages in the balloon.
	* If virtio balloon manages to release some memory, it will make the
	* system return and retry the allocation that forced the OOM killer
	* to run.
	*/
	static int virtballoon_oom_notify(struct notifier_block *self,
	unsigned long dummy, void *parm)
	{
	struct virtio_balloon *vb;
	unsigned long *freed;
	unsigned num_freed_pages;

	vb = container_of(self, struct virtio_balloon, nb);
	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
	return NOTIFY_OK;

	freed = parm;
	num_freed_pages = leak_balloon(vb, oom_pages);
	update_balloon_size(vb);
	*freed += num_freed_pages;

	return NOTIFY_OK;
	}

	static void update_balloon_stats_func(struct work_struct *work)
	{
	struct virtio_balloon *vb;

	vb = container_of(work, struct virtio_balloon,
	update_balloon_stats_work);
	stats_handle_request(vb);
	}

	static void update_balloon_size_func(struct work_struct *work)
	{
	struct virtio_balloon *vb;
	s64 diff;

	vb = container_of(work, struct virtio_balloon,
	update_balloon_size_work);
	diff = towards_target(vb);

	if (diff > 0)
	diff -= fill_balloon(vb, diff);
	else if (diff < 0)
	diff += leak_balloon(vb, -diff);
	update_balloon_size(vb);

	if (diff)
	queue_work(system_freezable_wq, work);
	}

	static int init_vqs(struct virtio_balloon *vb)
	{
	struct virtqueue *vqs[3];
	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
	static const char * const names[] = { "inflate", "deflate", "stats" };
	int err, nvqs;

	/*
	* We expect two virtqueues: inflate and deflate, and
	* optionally stat.
	*/
	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
	err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
	if (err)
	return err;

	vb->inflate_vq = vqs[0];
	vb->deflate_vq = vqs[1];
	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
	struct scatterlist sg;
	vb->stats_vq = vqs[2];

	/*
	* Prime this virtqueue with one buffer so the hypervisor can
	* use it to signal us later (it can't be broken yet!).
	*/
	sg_init_one(&sg, vb->stats, sizeof vb->stats);
	if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
	< 0)
	BUG();
	virtqueue_kick(vb->stats_vq);
	}
	return 0;
	}

	#ifdef CONFIG_BALLOON_COMPACTION
	/*
	* virtballoon_migratepage - perform the balloon page migration on behalf of
	* a compation thread. (called under page lock)
	* @vb_dev_info: the balloon device
	* @newpage: page that will replace the isolated page after migration finishes.
	* @page : the isolated (old) page that is about to be migrated to newpage.
	* @mode : compaction mode -- not used for balloon page migration.
	*
	* After a ballooned page gets isolated by compaction procedures, this is the
	* function that performs the page migration on behalf of a compaction thread
	* The page migration for virtio balloon is done in a simple swap fashion which
	* follows these two macro steps:
	* 1) insert newpage into vb->pages list and update the host about it;
	* 2) update the host about the old page removed from vb->pages list;
	*
	* This function preforms the balloon page migration task.
	* Called through balloon_mapping->a_ops->migratepage
	*/
	static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
	struct page newpage, struct page page, enum migrate_mode mode)
	{
	struct virtio_balloon *vb = container_of(vb_dev_info,
	struct virtio_balloon, vb_dev_info);
	unsigned long flags;

	/*
	* In order to avoid lock contention while migrating pages concurrently
	* to leak_balloon() or fill_balloon() we just give up the balloon_lock
	* this turn, as it is easier to retry the page migration later.
	* This also prevents fill_balloon() getting stuck into a mutex
	* recursion in the case it ends up triggering memory compaction
	* while it is attempting to inflate the ballon.
	*/
	if (!mutex_trylock(&vb->balloon_lock))
	return -EAGAIN;

	get_page(newpage); /* balloon reference */

	/* balloon's page migration 1st step -- inflate "newpage" */
	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
	balloon_page_insert(vb_dev_info, newpage);
	vb_dev_info->isolated_pages--;
	__count_vm_event(BALLOON_MIGRATE);
	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
	set_page_pfns(vb->pfns, newpage);
	tell_host(vb, vb->inflate_vq);

	/* balloon's page migration 2nd step -- deflate "page" */
	balloon_page_delete(page);
	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
	set_page_pfns(vb->pfns, page);
	tell_host(vb, vb->deflate_vq);

	mutex_unlock(&vb->balloon_lock);

	put_page(page); /* balloon reference */

	return MIGRATEPAGE_SUCCESS;
	}
	#endif /* CONFIG_BALLOON_COMPACTION */

	static int virtballoon_probe(struct virtio_device *vdev)
	{
	struct virtio_balloon *vb;
	int err;

	if (!vdev->config->get) {
	dev_err(&vdev->dev, "%s failure: config access disabled\n",
	__func__);
	return -EINVAL;
	}

	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
	if (!vb) {
	err = -ENOMEM;
	goto out;
	}

	INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
	INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
	spin_lock_init(&vb->stop_update_lock);
	vb->stop_update = false;
	vb->num_pages = 0;
	mutex_init(&vb->balloon_lock);
	init_waitqueue_head(&vb->acked);
	vb->vdev = vdev;

	balloon_devinfo_init(&vb->vb_dev_info);
	#ifdef CONFIG_BALLOON_COMPACTION
	vb->vb_dev_info.migratepage = virtballoon_migratepage;
	#endif

	err = init_vqs(vb);
	if (err)
	goto out_free_vb;

	vb->nb.notifier_call = virtballoon_oom_notify;
	vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
	err = register_oom_notifier(&vb->nb);
	if (err < 0)
	goto out_oom_notify;

	virtio_device_ready(vdev);

	return 0;

	out_oom_notify:
	vdev->config->del_vqs(vdev);
	out_free_vb:
	kfree(vb);
	out:
	return err;
	}

	static void remove_common(struct virtio_balloon *vb)
	{
	/* There might be pages left in the balloon: free them. */
	while (vb->num_pages)
	leak_balloon(vb, vb->num_pages);
	update_balloon_size(vb);

	/* Now we reset the device so we can clean up the queues. */
	vb->vdev->config->reset(vb->vdev);

	vb->vdev->config->del_vqs(vb->vdev);
	}

	static void virtballoon_remove(struct virtio_device *vdev)
	{
	struct virtio_balloon *vb = vdev->priv;

	unregister_oom_notifier(&vb->nb);

	spin_lock_irq(&vb->stop_update_lock);
	vb->stop_update = true;
	spin_unlock_irq(&vb->stop_update_lock);
	cancel_work_sync(&vb->update_balloon_size_work);
	cancel_work_sync(&vb->update_balloon_stats_work);

	remove_common(vb);
	kfree(vb);
	}

	#ifdef CONFIG_PM_SLEEP
	static int virtballoon_freeze(struct virtio_device *vdev)
	{
	struct virtio_balloon *vb = vdev->priv;

	/*
	* The workqueue is already frozen by the PM core before this
	* function is called.
	*/
	remove_common(vb);
	return 0;
	}

	static int virtballoon_restore(struct virtio_device *vdev)
	{
	struct virtio_balloon *vb = vdev->priv;
	int ret;

	ret = init_vqs(vdev->priv);
	if (ret)
	return ret;

	virtio_device_ready(vdev);

	if (towards_target(vb))
	virtballoon_changed(vdev);
	update_balloon_size(vb);
	return 0;
	}
	#endif

	static unsigned int features[] = {
	VIRTIO_BALLOON_F_MUST_TELL_HOST,
	VIRTIO_BALLOON_F_STATS_VQ,
	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
	};

	static struct virtio_driver virtio_balloon_driver = {
	.feature_table = features,
	.feature_table_size = ARRAY_SIZE(features),
	.driver.name = KBUILD_MODNAME,
	.driver.owner = THIS_MODULE,
	.id_table = id_table,
	.probe = virtballoon_probe,
	.remove = virtballoon_remove,
	.config_changed = virtballoon_changed,
	#ifdef CONFIG_PM_SLEEP
	.freeze = virtballoon_freeze,
	.restore = virtballoon_restore,
	#endif
	};

	module_virtio_driver(virtio_balloon_driver);
	MODULE_DEVICE_TABLE(virtio, id_table);
	MODULE_DESCRIPTION("Virtio balloon driver");
	MODULE_LICENSE("GPL");