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;
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 balloon_page_free(balloon_pfn_to_page(pfns[i]));
171 static void leak_balloon(struct virtio_balloon *vb, size_t num)
174 struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
176 /* We can only do one array worth at a time. */
177 num = min(num, ARRAY_SIZE(vb->pfns));
179 mutex_lock(&vb->balloon_lock);
180 for (vb->num_pfns = 0; vb->num_pfns < num;
181 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
182 page = balloon_page_dequeue(vb_dev_info);
185 set_page_pfns(vb->pfns + vb->num_pfns, page);
186 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
191 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
192 * is true, we *have* to do it in this order
194 if (vb->num_pfns != 0)
195 tell_host(vb, vb->deflate_vq);
196 mutex_unlock(&vb->balloon_lock);
197 release_pages_by_pfn(vb->pfns, vb->num_pfns);
200 static inline void update_stat(struct virtio_balloon *vb, int idx,
203 BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
204 vb->stats[idx].tag = tag;
205 vb->stats[idx].val = val;
208 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
210 static void update_balloon_stats(struct virtio_balloon *vb)
212 unsigned long events[NR_VM_EVENT_ITEMS];
216 all_vm_events(events);
219 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
220 pages_to_bytes(events[PSWPIN]));
221 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
222 pages_to_bytes(events[PSWPOUT]));
223 update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
224 update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
225 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
226 pages_to_bytes(i.freeram));
227 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
228 pages_to_bytes(i.totalram));
232 * While most virtqueues communicate guest-initiated requests to the hypervisor,
233 * the stats queue operates in reverse. The driver initializes the virtqueue
234 * with a single buffer. From that point forward, all conversations consist of
235 * a hypervisor request (a call to this function) which directs us to refill
236 * the virtqueue with a fresh stats buffer. Since stats collection can sleep,
237 * we notify our kthread which does the actual work via stats_handle_request().
239 static void stats_request(struct virtqueue *vq)
241 struct virtio_balloon *vb = vq->vdev->priv;
243 vb->need_stats_update = 1;
244 wake_up(&vb->config_change);
247 static void stats_handle_request(struct virtio_balloon *vb)
249 struct virtqueue *vq;
250 struct scatterlist sg;
253 vb->need_stats_update = 0;
254 update_balloon_stats(vb);
257 if (!virtqueue_get_buf(vq, &len))
259 sg_init_one(&sg, vb->stats, sizeof(vb->stats));
260 if (virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL) < 0)
265 static void virtballoon_changed(struct virtio_device *vdev)
267 struct virtio_balloon *vb = vdev->priv;
269 wake_up(&vb->config_change);
272 static inline s64 towards_target(struct virtio_balloon *vb)
277 vb->vdev->config->get(vb->vdev,
278 offsetof(struct virtio_balloon_config, num_pages),
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 vb->vdev->config->set(vb->vdev,
289 offsetof(struct virtio_balloon_config, actual),
290 &actual, sizeof(actual));
293 static int balloon(void *_vballoon)
295 struct virtio_balloon *vb = _vballoon;
298 while (!kthread_should_stop()) {
302 wait_event_interruptible(vb->config_change,
303 (diff = towards_target(vb)) != 0
304 || vb->need_stats_update
305 || kthread_should_stop()
306 || freezing(current));
307 if (vb->need_stats_update)
308 stats_handle_request(vb);
310 fill_balloon(vb, diff);
312 leak_balloon(vb, -diff);
313 update_balloon_size(vb);
316 * For large balloon changes, we could spend a lot of time
317 * and always have work to do. Be nice if preempt disabled.
324 static int init_vqs(struct virtio_balloon *vb)
326 struct virtqueue *vqs[3];
327 vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
328 const char *names[] = { "inflate", "deflate", "stats" };
332 * We expect two virtqueues: inflate and deflate, and
335 nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
336 err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
340 vb->inflate_vq = vqs[0];
341 vb->deflate_vq = vqs[1];
342 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
343 struct scatterlist sg;
344 vb->stats_vq = vqs[2];
347 * Prime this virtqueue with one buffer so the hypervisor can
348 * use it to signal us later.
350 sg_init_one(&sg, vb->stats, sizeof vb->stats);
351 if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
354 virtqueue_kick(vb->stats_vq);
359 static const struct address_space_operations virtio_balloon_aops;
360 #ifdef CONFIG_BALLOON_COMPACTION
362 * virtballoon_migratepage - perform the balloon page migration on behalf of
363 * a compation thread. (called under page lock)
364 * @mapping: the page->mapping which will be assigned to the new migrated page.
365 * @newpage: page that will replace the isolated page after migration finishes.
366 * @page : the isolated (old) page that is about to be migrated to newpage.
367 * @mode : compaction mode -- not used for balloon page migration.
369 * After a ballooned page gets isolated by compaction procedures, this is the
370 * function that performs the page migration on behalf of a compaction thread
371 * The page migration for virtio balloon is done in a simple swap fashion which
372 * follows these two macro steps:
373 * 1) insert newpage into vb->pages list and update the host about it;
374 * 2) update the host about the old page removed from vb->pages list;
376 * This function preforms the balloon page migration task.
377 * Called through balloon_mapping->a_ops->migratepage
379 int virtballoon_migratepage(struct address_space *mapping,
380 struct page *newpage, struct page *page, enum migrate_mode mode)
382 struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
383 struct virtio_balloon *vb;
386 BUG_ON(!vb_dev_info);
388 vb = vb_dev_info->balloon_device;
391 * In order to avoid lock contention while migrating pages concurrently
392 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
393 * this turn, as it is easier to retry the page migration later.
394 * This also prevents fill_balloon() getting stuck into a mutex
395 * recursion in the case it ends up triggering memory compaction
396 * while it is attempting to inflate the ballon.
398 if (!mutex_trylock(&vb->balloon_lock))
401 /* balloon's page migration 1st step -- inflate "newpage" */
402 spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
403 balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
404 vb_dev_info->isolated_pages--;
405 spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
406 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
407 set_page_pfns(vb->pfns, newpage);
408 tell_host(vb, vb->inflate_vq);
411 * balloon's page migration 2nd step -- deflate "page"
413 * It's safe to delete page->lru here because this page is at
414 * an isolated migration list, and this step is expected to happen here
416 balloon_page_delete(page);
417 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
418 set_page_pfns(vb->pfns, page);
419 tell_host(vb, vb->deflate_vq);
421 mutex_unlock(&vb->balloon_lock);
423 return MIGRATEPAGE_BALLOON_SUCCESS;
426 /* define the balloon_mapping->a_ops callback to allow balloon page migration */
427 static const struct address_space_operations virtio_balloon_aops = {
428 .migratepage = virtballoon_migratepage,
430 #endif /* CONFIG_BALLOON_COMPACTION */
432 static int virtballoon_probe(struct virtio_device *vdev)
434 struct virtio_balloon *vb;
435 struct address_space *vb_mapping;
436 struct balloon_dev_info *vb_devinfo;
439 vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
446 mutex_init(&vb->balloon_lock);
447 init_waitqueue_head(&vb->config_change);
448 init_waitqueue_head(&vb->acked);
450 vb->need_stats_update = 0;
452 vb_devinfo = balloon_devinfo_alloc(vb);
453 if (IS_ERR(vb_devinfo)) {
454 err = PTR_ERR(vb_devinfo);
458 vb_mapping = balloon_mapping_alloc(vb_devinfo,
459 (balloon_compaction_check()) ?
460 &virtio_balloon_aops : NULL);
461 if (IS_ERR(vb_mapping)) {
463 * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
464 * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
466 err = PTR_ERR(vb_mapping);
467 if (err != -EOPNOTSUPP)
468 goto out_free_vb_devinfo;
471 vb->vb_dev_info = vb_devinfo;
475 goto out_free_vb_mapping;
477 vb->thread = kthread_run(balloon, vb, "vballoon");
478 if (IS_ERR(vb->thread)) {
479 err = PTR_ERR(vb->thread);
486 vdev->config->del_vqs(vdev);
488 balloon_mapping_free(vb_mapping);
490 balloon_devinfo_free(vb_devinfo);
497 static void remove_common(struct virtio_balloon *vb)
499 /* There might be pages left in the balloon: free them. */
500 while (vb->num_pages)
501 leak_balloon(vb, vb->num_pages);
502 update_balloon_size(vb);
504 /* Now we reset the device so we can clean up the queues. */
505 vb->vdev->config->reset(vb->vdev);
507 vb->vdev->config->del_vqs(vb->vdev);
510 static void virtballoon_remove(struct virtio_device *vdev)
512 struct virtio_balloon *vb = vdev->priv;
514 kthread_stop(vb->thread);
516 balloon_mapping_free(vb->vb_dev_info->mapping);
517 balloon_devinfo_free(vb->vb_dev_info);
522 static int virtballoon_freeze(struct virtio_device *vdev)
524 struct virtio_balloon *vb = vdev->priv;
527 * The kthread is already frozen by the PM core before this
528 * function is called.
535 static int virtballoon_restore(struct virtio_device *vdev)
537 struct virtio_balloon *vb = vdev->priv;
540 ret = init_vqs(vdev->priv);
544 fill_balloon(vb, towards_target(vb));
545 update_balloon_size(vb);
550 static unsigned int features[] = {
551 VIRTIO_BALLOON_F_MUST_TELL_HOST,
552 VIRTIO_BALLOON_F_STATS_VQ,
555 static struct virtio_driver virtio_balloon_driver = {
556 .feature_table = features,
557 .feature_table_size = ARRAY_SIZE(features),
558 .driver.name = KBUILD_MODNAME,
559 .driver.owner = THIS_MODULE,
560 .id_table = id_table,
561 .probe = virtballoon_probe,
562 .remove = virtballoon_remove,
563 .config_changed = virtballoon_changed,
565 .freeze = virtballoon_freeze,
566 .restore = virtballoon_restore,
570 module_virtio_driver(virtio_balloon_driver);
571 MODULE_DEVICE_TABLE(virtio, id_table);
572 MODULE_DESCRIPTION("Virtio balloon driver");
573 MODULE_LICENSE("GPL");