2 * Virtio balloon implementation, inspired by Dor Laor and Marcelo
3 * Tosatti's implementations.
5 * Copyright 2008 Rusty Russell IBM Corporation
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
22 #include <linux/virtio.h>
23 #include <linux/virtio_balloon.h>
24 #include <linux/swap.h>
25 #include <linux/kthread.h>
26 #include <linux/freezer.h>
27 #include <linux/delay.h>
28 #include <linux/slab.h>
29 #include <linux/module.h>
30 #include <linux/balloon_compaction.h>
33 * Balloon device works in 4K page units. So each page is pointed to by
34 * multiple balloon pages. All memory counters in this driver are in balloon
37 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
38 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
42 struct virtio_device *vdev;
43 struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
45 /* Where the ballooning thread waits for config to change. */
46 wait_queue_head_t config_change;
48 /* The thread servicing the balloon. */
49 struct task_struct *thread;
51 /* Waiting for host to ack the pages we released. */
52 wait_queue_head_t acked;
54 /* Number of balloon pages we've told the Host we're not using. */
55 unsigned int num_pages;
57 * The pages we've told the Host we're not using are enqueued
58 * at vb_dev_info->pages list.
59 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
62 struct balloon_dev_info *vb_dev_info;
64 /* Synchronize access/update to this struct virtio_balloon elements */
65 struct mutex balloon_lock;
67 /* The array of pfns we tell the Host about. */
68 unsigned int num_pfns;
69 u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
71 /* Memory statistics */
72 int need_stats_update;
73 struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
76 static struct virtio_device_id id_table[] = {
77 { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
81 static u32 page_to_balloon_pfn(struct page *page)
83 unsigned long pfn = page_to_pfn(page);
85 BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
86 /* Convert pfn from Linux page size to balloon page size. */
87 return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
90 static struct page *balloon_pfn_to_page(u32 pfn)
92 BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
93 return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
96 static void balloon_ack(struct virtqueue *vq)
98 struct virtio_balloon *vb = vq->vdev->priv;
103 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
105 struct scatterlist sg;
108 sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
110 /* We should always be able to add one buffer to an empty queue. */
111 if (virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL) < 0)
115 /* When host has read buffer, this completes via balloon_ack */
116 wait_event(vb->acked, virtqueue_get_buf(vq, &len));
119 static void set_page_pfns(u32 pfns[], struct page *page)
123 /* Set balloon pfns pointing at this page.
124 * Note that the first pfn points at start of the page. */
125 for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
126 pfns[i] = page_to_balloon_pfn(page) + i;
129 static void fill_balloon(struct virtio_balloon *vb, size_t num)
131 struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
133 /* We can only do one array worth at a time. */
134 num = min(num, ARRAY_SIZE(vb->pfns));
136 mutex_lock(&vb->balloon_lock);
137 for (vb->num_pfns = 0; vb->num_pfns < num;
138 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
139 struct page *page = balloon_page_enqueue(vb_dev_info);
142 dev_info_ratelimited(&vb->vdev->dev,
143 "Out of puff! Can't get %u pages\n",
144 VIRTIO_BALLOON_PAGES_PER_PAGE);
145 /* Sleep for at least 1/5 of a second before retry. */
149 set_page_pfns(vb->pfns + vb->num_pfns, page);
150 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
151 adjust_managed_page_count(page, -1);
154 /* Did we get any? */
155 if (vb->num_pfns != 0)
156 tell_host(vb, vb->inflate_vq);
157 mutex_unlock(&vb->balloon_lock);
160 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
164 /* Find pfns pointing at start of each page, get pages and free them. */
165 for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
166 struct page *page = balloon_pfn_to_page(pfns[i]);
167 balloon_page_free(page);
168 adjust_managed_page_count(page, 1);
172 static void leak_balloon(struct virtio_balloon *vb, size_t num)
175 struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
177 /* We can only do one array worth at a time. */
178 num = min(num, ARRAY_SIZE(vb->pfns));
180 mutex_lock(&vb->balloon_lock);
181 for (vb->num_pfns = 0; vb->num_pfns < num;
182 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
183 page = balloon_page_dequeue(vb_dev_info);
186 set_page_pfns(vb->pfns + vb->num_pfns, page);
187 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
192 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
193 * is true, we *have* to do it in this order
195 if (vb->num_pfns != 0)
196 tell_host(vb, vb->deflate_vq);
197 mutex_unlock(&vb->balloon_lock);
198 release_pages_by_pfn(vb->pfns, vb->num_pfns);
201 static inline void update_stat(struct virtio_balloon *vb, int idx,
204 BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
205 vb->stats[idx].tag = tag;
206 vb->stats[idx].val = val;
209 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
211 static void update_balloon_stats(struct virtio_balloon *vb)
213 unsigned long events[NR_VM_EVENT_ITEMS];
217 all_vm_events(events);
220 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
221 pages_to_bytes(events[PSWPIN]));
222 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
223 pages_to_bytes(events[PSWPOUT]));
224 update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
225 update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
226 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
227 pages_to_bytes(i.freeram));
228 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
229 pages_to_bytes(i.totalram));
233 * While most virtqueues communicate guest-initiated requests to the hypervisor,
234 * the stats queue operates in reverse. The driver initializes the virtqueue
235 * with a single buffer. From that point forward, all conversations consist of
236 * a hypervisor request (a call to this function) which directs us to refill
237 * the virtqueue with a fresh stats buffer. Since stats collection can sleep,
238 * we notify our kthread which does the actual work via stats_handle_request().
240 static void stats_request(struct virtqueue *vq)
242 struct virtio_balloon *vb = vq->vdev->priv;
244 vb->need_stats_update = 1;
245 wake_up(&vb->config_change);
248 static void stats_handle_request(struct virtio_balloon *vb)
250 struct virtqueue *vq;
251 struct scatterlist sg;
254 vb->need_stats_update = 0;
255 update_balloon_stats(vb);
258 if (!virtqueue_get_buf(vq, &len))
260 sg_init_one(&sg, vb->stats, sizeof(vb->stats));
261 if (virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL) < 0)
266 static void virtballoon_changed(struct virtio_device *vdev)
268 struct virtio_balloon *vb = vdev->priv;
270 wake_up(&vb->config_change);
273 static inline s64 towards_target(struct virtio_balloon *vb)
278 virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages, &v);
280 target = le32_to_cpu(v);
281 return target - vb->num_pages;
284 static void update_balloon_size(struct virtio_balloon *vb)
286 __le32 actual = cpu_to_le32(vb->num_pages);
288 virtio_cwrite(vb->vdev, struct virtio_balloon_config, num_pages,
292 static int balloon(void *_vballoon)
294 struct virtio_balloon *vb = _vballoon;
297 while (!kthread_should_stop()) {
301 wait_event_interruptible(vb->config_change,
302 (diff = towards_target(vb)) != 0
303 || vb->need_stats_update
304 || kthread_should_stop()
305 || freezing(current));
306 if (vb->need_stats_update)
307 stats_handle_request(vb);
309 fill_balloon(vb, diff);
311 leak_balloon(vb, -diff);
312 update_balloon_size(vb);
317 static int init_vqs(struct virtio_balloon *vb)
319 struct virtqueue *vqs[3];
320 vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
321 const char *names[] = { "inflate", "deflate", "stats" };
325 * We expect two virtqueues: inflate and deflate, and
328 nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
329 err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
333 vb->inflate_vq = vqs[0];
334 vb->deflate_vq = vqs[1];
335 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
336 struct scatterlist sg;
337 vb->stats_vq = vqs[2];
340 * Prime this virtqueue with one buffer so the hypervisor can
341 * use it to signal us later.
343 sg_init_one(&sg, vb->stats, sizeof vb->stats);
344 if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
347 virtqueue_kick(vb->stats_vq);
352 static const struct address_space_operations virtio_balloon_aops;
353 #ifdef CONFIG_BALLOON_COMPACTION
355 * virtballoon_migratepage - perform the balloon page migration on behalf of
356 * a compation thread. (called under page lock)
357 * @mapping: the page->mapping which will be assigned to the new migrated page.
358 * @newpage: page that will replace the isolated page after migration finishes.
359 * @page : the isolated (old) page that is about to be migrated to newpage.
360 * @mode : compaction mode -- not used for balloon page migration.
362 * After a ballooned page gets isolated by compaction procedures, this is the
363 * function that performs the page migration on behalf of a compaction thread
364 * The page migration for virtio balloon is done in a simple swap fashion which
365 * follows these two macro steps:
366 * 1) insert newpage into vb->pages list and update the host about it;
367 * 2) update the host about the old page removed from vb->pages list;
369 * This function preforms the balloon page migration task.
370 * Called through balloon_mapping->a_ops->migratepage
372 static int virtballoon_migratepage(struct address_space *mapping,
373 struct page *newpage, struct page *page, enum migrate_mode mode)
375 struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
376 struct virtio_balloon *vb;
379 BUG_ON(!vb_dev_info);
381 vb = vb_dev_info->balloon_device;
384 * In order to avoid lock contention while migrating pages concurrently
385 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
386 * this turn, as it is easier to retry the page migration later.
387 * This also prevents fill_balloon() getting stuck into a mutex
388 * recursion in the case it ends up triggering memory compaction
389 * while it is attempting to inflate the ballon.
391 if (!mutex_trylock(&vb->balloon_lock))
394 /* balloon's page migration 1st step -- inflate "newpage" */
395 spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
396 balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
397 vb_dev_info->isolated_pages--;
398 spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
399 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
400 set_page_pfns(vb->pfns, newpage);
401 tell_host(vb, vb->inflate_vq);
404 * balloon's page migration 2nd step -- deflate "page"
406 * It's safe to delete page->lru here because this page is at
407 * an isolated migration list, and this step is expected to happen here
409 balloon_page_delete(page);
410 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
411 set_page_pfns(vb->pfns, page);
412 tell_host(vb, vb->deflate_vq);
414 mutex_unlock(&vb->balloon_lock);
416 return MIGRATEPAGE_BALLOON_SUCCESS;
419 /* define the balloon_mapping->a_ops callback to allow balloon page migration */
420 static const struct address_space_operations virtio_balloon_aops = {
421 .migratepage = virtballoon_migratepage,
423 #endif /* CONFIG_BALLOON_COMPACTION */
425 static int virtballoon_probe(struct virtio_device *vdev)
427 struct virtio_balloon *vb;
428 struct address_space *vb_mapping;
429 struct balloon_dev_info *vb_devinfo;
432 vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
439 mutex_init(&vb->balloon_lock);
440 init_waitqueue_head(&vb->config_change);
441 init_waitqueue_head(&vb->acked);
443 vb->need_stats_update = 0;
445 vb_devinfo = balloon_devinfo_alloc(vb);
446 if (IS_ERR(vb_devinfo)) {
447 err = PTR_ERR(vb_devinfo);
451 vb_mapping = balloon_mapping_alloc(vb_devinfo,
452 (balloon_compaction_check()) ?
453 &virtio_balloon_aops : NULL);
454 if (IS_ERR(vb_mapping)) {
456 * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
457 * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
459 err = PTR_ERR(vb_mapping);
460 if (err != -EOPNOTSUPP)
461 goto out_free_vb_devinfo;
464 vb->vb_dev_info = vb_devinfo;
468 goto out_free_vb_mapping;
470 vb->thread = kthread_run(balloon, vb, "vballoon");
471 if (IS_ERR(vb->thread)) {
472 err = PTR_ERR(vb->thread);
479 vdev->config->del_vqs(vdev);
481 balloon_mapping_free(vb_mapping);
483 balloon_devinfo_free(vb_devinfo);
490 static void remove_common(struct virtio_balloon *vb)
492 /* There might be pages left in the balloon: free them. */
493 while (vb->num_pages)
494 leak_balloon(vb, vb->num_pages);
495 update_balloon_size(vb);
497 /* Now we reset the device so we can clean up the queues. */
498 vb->vdev->config->reset(vb->vdev);
500 vb->vdev->config->del_vqs(vb->vdev);
503 static void virtballoon_remove(struct virtio_device *vdev)
505 struct virtio_balloon *vb = vdev->priv;
507 kthread_stop(vb->thread);
509 balloon_mapping_free(vb->vb_dev_info->mapping);
510 balloon_devinfo_free(vb->vb_dev_info);
514 #ifdef CONFIG_PM_SLEEP
515 static int virtballoon_freeze(struct virtio_device *vdev)
517 struct virtio_balloon *vb = vdev->priv;
520 * The kthread is already frozen by the PM core before this
521 * function is called.
528 static int virtballoon_restore(struct virtio_device *vdev)
530 struct virtio_balloon *vb = vdev->priv;
533 ret = init_vqs(vdev->priv);
537 fill_balloon(vb, towards_target(vb));
538 update_balloon_size(vb);
543 static unsigned int features[] = {
544 VIRTIO_BALLOON_F_MUST_TELL_HOST,
545 VIRTIO_BALLOON_F_STATS_VQ,
548 static struct virtio_driver virtio_balloon_driver = {
549 .feature_table = features,
550 .feature_table_size = ARRAY_SIZE(features),
551 .driver.name = KBUILD_MODNAME,
552 .driver.owner = THIS_MODULE,
553 .id_table = id_table,
554 .probe = virtballoon_probe,
555 .remove = virtballoon_remove,
556 .config_changed = virtballoon_changed,
557 #ifdef CONFIG_PM_SLEEP
558 .freeze = virtballoon_freeze,
559 .restore = virtballoon_restore,
563 module_virtio_driver(virtio_balloon_driver);
564 MODULE_DEVICE_TABLE(virtio, id_table);
565 MODULE_DESCRIPTION("Virtio balloon driver");
566 MODULE_LICENSE("GPL");