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>
31 #include <linux/oom.h>
34 * Balloon device works in 4K page units. So each page is pointed to by
35 * multiple balloon pages. All memory counters in this driver are in balloon
38 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
39 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
40 #define OOM_VBALLOON_DEFAULT_PAGES 256
41 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
43 static int oom_pages
= OOM_VBALLOON_DEFAULT_PAGES
;
44 module_param(oom_pages
, int, S_IRUSR
| S_IWUSR
);
45 MODULE_PARM_DESC(oom_pages
, "pages to free on OOM");
47 struct virtio_balloon
{
48 struct virtio_device
*vdev
;
49 struct virtqueue
*inflate_vq
, *deflate_vq
, *stats_vq
;
51 /* Where the ballooning thread waits for config to change. */
52 wait_queue_head_t config_change
;
54 /* The thread servicing the balloon. */
55 struct task_struct
*thread
;
57 /* Waiting for host to ack the pages we released. */
58 wait_queue_head_t acked
;
60 /* Number of balloon pages we've told the Host we're not using. */
61 unsigned int num_pages
;
63 * The pages we've told the Host we're not using are enqueued
64 * at vb_dev_info->pages list.
65 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
68 struct balloon_dev_info vb_dev_info
;
70 /* Synchronize access/update to this struct virtio_balloon elements */
71 struct mutex balloon_lock
;
73 /* The array of pfns we tell the Host about. */
74 unsigned int num_pfns
;
75 u32 pfns
[VIRTIO_BALLOON_ARRAY_PFNS_MAX
];
77 /* Memory statistics */
78 int need_stats_update
;
79 struct virtio_balloon_stat stats
[VIRTIO_BALLOON_S_NR
];
81 /* To register callback in oom notifier call chain */
82 struct notifier_block nb
;
85 static struct virtio_device_id id_table
[] = {
86 { VIRTIO_ID_BALLOON
, VIRTIO_DEV_ANY_ID
},
90 static u32
page_to_balloon_pfn(struct page
*page
)
92 unsigned long pfn
= page_to_pfn(page
);
94 BUILD_BUG_ON(PAGE_SHIFT
< VIRTIO_BALLOON_PFN_SHIFT
);
95 /* Convert pfn from Linux page size to balloon page size. */
96 return pfn
* VIRTIO_BALLOON_PAGES_PER_PAGE
;
99 static struct page
*balloon_pfn_to_page(u32 pfn
)
101 BUG_ON(pfn
% VIRTIO_BALLOON_PAGES_PER_PAGE
);
102 return pfn_to_page(pfn
/ VIRTIO_BALLOON_PAGES_PER_PAGE
);
105 static void balloon_ack(struct virtqueue
*vq
)
107 struct virtio_balloon
*vb
= vq
->vdev
->priv
;
112 static void tell_host(struct virtio_balloon
*vb
, struct virtqueue
*vq
)
114 struct scatterlist sg
;
117 sg_init_one(&sg
, vb
->pfns
, sizeof(vb
->pfns
[0]) * vb
->num_pfns
);
119 /* We should always be able to add one buffer to an empty queue. */
120 virtqueue_add_outbuf(vq
, &sg
, 1, vb
, GFP_KERNEL
);
123 /* When host has read buffer, this completes via balloon_ack */
124 wait_event(vb
->acked
, virtqueue_get_buf(vq
, &len
));
127 static void set_page_pfns(u32 pfns
[], struct page
*page
)
131 /* Set balloon pfns pointing at this page.
132 * Note that the first pfn points at start of the page. */
133 for (i
= 0; i
< VIRTIO_BALLOON_PAGES_PER_PAGE
; i
++)
134 pfns
[i
] = page_to_balloon_pfn(page
) + i
;
137 static void fill_balloon(struct virtio_balloon
*vb
, size_t num
)
139 struct balloon_dev_info
*vb_dev_info
= &vb
->vb_dev_info
;
141 /* We can only do one array worth at a time. */
142 num
= min(num
, ARRAY_SIZE(vb
->pfns
));
144 mutex_lock(&vb
->balloon_lock
);
145 for (vb
->num_pfns
= 0; vb
->num_pfns
< num
;
146 vb
->num_pfns
+= VIRTIO_BALLOON_PAGES_PER_PAGE
) {
147 struct page
*page
= balloon_page_enqueue(vb_dev_info
);
150 dev_info_ratelimited(&vb
->vdev
->dev
,
151 "Out of puff! Can't get %u pages\n",
152 VIRTIO_BALLOON_PAGES_PER_PAGE
);
153 /* Sleep for at least 1/5 of a second before retry. */
157 set_page_pfns(vb
->pfns
+ vb
->num_pfns
, page
);
158 vb
->num_pages
+= VIRTIO_BALLOON_PAGES_PER_PAGE
;
159 adjust_managed_page_count(page
, -1);
162 /* Did we get any? */
163 if (vb
->num_pfns
!= 0)
164 tell_host(vb
, vb
->inflate_vq
);
165 mutex_unlock(&vb
->balloon_lock
);
168 static void release_pages_by_pfn(const u32 pfns
[], unsigned int num
)
172 /* Find pfns pointing at start of each page, get pages and free them. */
173 for (i
= 0; i
< num
; i
+= VIRTIO_BALLOON_PAGES_PER_PAGE
) {
174 struct page
*page
= balloon_pfn_to_page(pfns
[i
]);
175 adjust_managed_page_count(page
, 1);
176 put_page(page
); /* balloon reference */
180 static unsigned leak_balloon(struct virtio_balloon
*vb
, size_t num
)
182 unsigned num_freed_pages
;
184 struct balloon_dev_info
*vb_dev_info
= &vb
->vb_dev_info
;
186 /* We can only do one array worth at a time. */
187 num
= min(num
, ARRAY_SIZE(vb
->pfns
));
189 mutex_lock(&vb
->balloon_lock
);
190 for (vb
->num_pfns
= 0; vb
->num_pfns
< num
;
191 vb
->num_pfns
+= VIRTIO_BALLOON_PAGES_PER_PAGE
) {
192 page
= balloon_page_dequeue(vb_dev_info
);
195 set_page_pfns(vb
->pfns
+ vb
->num_pfns
, page
);
196 vb
->num_pages
-= VIRTIO_BALLOON_PAGES_PER_PAGE
;
199 num_freed_pages
= vb
->num_pfns
;
202 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
203 * is true, we *have* to do it in this order
205 if (vb
->num_pfns
!= 0)
206 tell_host(vb
, vb
->deflate_vq
);
207 mutex_unlock(&vb
->balloon_lock
);
208 release_pages_by_pfn(vb
->pfns
, vb
->num_pfns
);
209 return num_freed_pages
;
212 static inline void update_stat(struct virtio_balloon
*vb
, int idx
,
215 BUG_ON(idx
>= VIRTIO_BALLOON_S_NR
);
216 vb
->stats
[idx
].tag
= tag
;
217 vb
->stats
[idx
].val
= val
;
220 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
222 static void update_balloon_stats(struct virtio_balloon
*vb
)
224 unsigned long events
[NR_VM_EVENT_ITEMS
];
228 all_vm_events(events
);
231 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_SWAP_IN
,
232 pages_to_bytes(events
[PSWPIN
]));
233 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_SWAP_OUT
,
234 pages_to_bytes(events
[PSWPOUT
]));
235 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MAJFLT
, events
[PGMAJFAULT
]);
236 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MINFLT
, events
[PGFAULT
]);
237 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MEMFREE
,
238 pages_to_bytes(i
.freeram
));
239 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MEMTOT
,
240 pages_to_bytes(i
.totalram
));
244 * While most virtqueues communicate guest-initiated requests to the hypervisor,
245 * the stats queue operates in reverse. The driver initializes the virtqueue
246 * with a single buffer. From that point forward, all conversations consist of
247 * a hypervisor request (a call to this function) which directs us to refill
248 * the virtqueue with a fresh stats buffer. Since stats collection can sleep,
249 * we notify our kthread which does the actual work via stats_handle_request().
251 static void stats_request(struct virtqueue
*vq
)
253 struct virtio_balloon
*vb
= vq
->vdev
->priv
;
255 vb
->need_stats_update
= 1;
256 wake_up(&vb
->config_change
);
259 static void stats_handle_request(struct virtio_balloon
*vb
)
261 struct virtqueue
*vq
;
262 struct scatterlist sg
;
265 vb
->need_stats_update
= 0;
266 update_balloon_stats(vb
);
269 if (!virtqueue_get_buf(vq
, &len
))
271 sg_init_one(&sg
, vb
->stats
, sizeof(vb
->stats
));
272 virtqueue_add_outbuf(vq
, &sg
, 1, vb
, GFP_KERNEL
);
276 static void virtballoon_changed(struct virtio_device
*vdev
)
278 struct virtio_balloon
*vb
= vdev
->priv
;
280 wake_up(&vb
->config_change
);
283 static inline s64
towards_target(struct virtio_balloon
*vb
)
288 virtio_cread(vb
->vdev
, struct virtio_balloon_config
, num_pages
, &v
);
290 target
= le32_to_cpu(v
);
291 return target
- vb
->num_pages
;
294 static void update_balloon_size(struct virtio_balloon
*vb
)
296 __le32 actual
= cpu_to_le32(vb
->num_pages
);
298 virtio_cwrite(vb
->vdev
, struct virtio_balloon_config
, actual
,
303 * virtballoon_oom_notify - release pages when system is under severe
304 * memory pressure (called from out_of_memory())
305 * @self : notifier block struct
307 * @parm : returned - number of freed pages
309 * The balancing of memory by use of the virtio balloon should not cause
310 * the termination of processes while there are pages in the balloon.
311 * If virtio balloon manages to release some memory, it will make the
312 * system return and retry the allocation that forced the OOM killer
315 static int virtballoon_oom_notify(struct notifier_block
*self
,
316 unsigned long dummy
, void *parm
)
318 struct virtio_balloon
*vb
;
319 unsigned long *freed
;
320 unsigned num_freed_pages
;
322 vb
= container_of(self
, struct virtio_balloon
, nb
);
323 if (!virtio_has_feature(vb
->vdev
, VIRTIO_BALLOON_F_DEFLATE_ON_OOM
))
327 num_freed_pages
= leak_balloon(vb
, oom_pages
);
328 update_balloon_size(vb
);
329 *freed
+= num_freed_pages
;
334 static int balloon(void *_vballoon
)
336 struct virtio_balloon
*vb
= _vballoon
;
339 while (!kthread_should_stop()) {
343 wait_event_interruptible(vb
->config_change
,
344 (diff
= towards_target(vb
)) != 0
345 || vb
->need_stats_update
346 || kthread_should_stop()
347 || freezing(current
));
348 if (vb
->need_stats_update
)
349 stats_handle_request(vb
);
351 fill_balloon(vb
, diff
);
353 leak_balloon(vb
, -diff
);
354 update_balloon_size(vb
);
357 * For large balloon changes, we could spend a lot of time
358 * and always have work to do. Be nice if preempt disabled.
365 static int init_vqs(struct virtio_balloon
*vb
)
367 struct virtqueue
*vqs
[3];
368 vq_callback_t
*callbacks
[] = { balloon_ack
, balloon_ack
, stats_request
};
369 const char *names
[] = { "inflate", "deflate", "stats" };
373 * We expect two virtqueues: inflate and deflate, and
376 nvqs
= virtio_has_feature(vb
->vdev
, VIRTIO_BALLOON_F_STATS_VQ
) ? 3 : 2;
377 err
= vb
->vdev
->config
->find_vqs(vb
->vdev
, nvqs
, vqs
, callbacks
, names
);
381 vb
->inflate_vq
= vqs
[0];
382 vb
->deflate_vq
= vqs
[1];
383 if (virtio_has_feature(vb
->vdev
, VIRTIO_BALLOON_F_STATS_VQ
)) {
384 struct scatterlist sg
;
385 vb
->stats_vq
= vqs
[2];
388 * Prime this virtqueue with one buffer so the hypervisor can
389 * use it to signal us later (it can't be broken yet!).
391 sg_init_one(&sg
, vb
->stats
, sizeof vb
->stats
);
392 if (virtqueue_add_outbuf(vb
->stats_vq
, &sg
, 1, vb
, GFP_KERNEL
)
395 virtqueue_kick(vb
->stats_vq
);
400 #ifdef CONFIG_BALLOON_COMPACTION
402 * virtballoon_migratepage - perform the balloon page migration on behalf of
403 * a compation thread. (called under page lock)
404 * @vb_dev_info: the balloon device
405 * @newpage: page that will replace the isolated page after migration finishes.
406 * @page : the isolated (old) page that is about to be migrated to newpage.
407 * @mode : compaction mode -- not used for balloon page migration.
409 * After a ballooned page gets isolated by compaction procedures, this is the
410 * function that performs the page migration on behalf of a compaction thread
411 * The page migration for virtio balloon is done in a simple swap fashion which
412 * follows these two macro steps:
413 * 1) insert newpage into vb->pages list and update the host about it;
414 * 2) update the host about the old page removed from vb->pages list;
416 * This function preforms the balloon page migration task.
417 * Called through balloon_mapping->a_ops->migratepage
419 static int virtballoon_migratepage(struct balloon_dev_info
*vb_dev_info
,
420 struct page
*newpage
, struct page
*page
, enum migrate_mode mode
)
422 struct virtio_balloon
*vb
= container_of(vb_dev_info
,
423 struct virtio_balloon
, vb_dev_info
);
427 * In order to avoid lock contention while migrating pages concurrently
428 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
429 * this turn, as it is easier to retry the page migration later.
430 * This also prevents fill_balloon() getting stuck into a mutex
431 * recursion in the case it ends up triggering memory compaction
432 * while it is attempting to inflate the ballon.
434 if (!mutex_trylock(&vb
->balloon_lock
))
437 get_page(newpage
); /* balloon reference */
439 /* balloon's page migration 1st step -- inflate "newpage" */
440 spin_lock_irqsave(&vb_dev_info
->pages_lock
, flags
);
441 balloon_page_insert(vb_dev_info
, newpage
);
442 vb_dev_info
->isolated_pages
--;
443 __count_vm_event(BALLOON_MIGRATE
);
444 spin_unlock_irqrestore(&vb_dev_info
->pages_lock
, flags
);
445 vb
->num_pfns
= VIRTIO_BALLOON_PAGES_PER_PAGE
;
446 set_page_pfns(vb
->pfns
, newpage
);
447 tell_host(vb
, vb
->inflate_vq
);
449 /* balloon's page migration 2nd step -- deflate "page" */
450 balloon_page_delete(page
);
451 vb
->num_pfns
= VIRTIO_BALLOON_PAGES_PER_PAGE
;
452 set_page_pfns(vb
->pfns
, page
);
453 tell_host(vb
, vb
->deflate_vq
);
455 mutex_unlock(&vb
->balloon_lock
);
457 put_page(page
); /* balloon reference */
459 return MIGRATEPAGE_SUCCESS
;
461 #endif /* CONFIG_BALLOON_COMPACTION */
463 static int virtballoon_probe(struct virtio_device
*vdev
)
465 struct virtio_balloon
*vb
;
468 if (!vdev
->config
->get
) {
469 dev_err(&vdev
->dev
, "%s failure: config access disabled\n",
474 vdev
->priv
= vb
= kmalloc(sizeof(*vb
), GFP_KERNEL
);
481 mutex_init(&vb
->balloon_lock
);
482 init_waitqueue_head(&vb
->config_change
);
483 init_waitqueue_head(&vb
->acked
);
485 vb
->need_stats_update
= 0;
487 balloon_devinfo_init(&vb
->vb_dev_info
);
488 #ifdef CONFIG_BALLOON_COMPACTION
489 vb
->vb_dev_info
.migratepage
= virtballoon_migratepage
;
496 vb
->nb
.notifier_call
= virtballoon_oom_notify
;
497 vb
->nb
.priority
= VIRTBALLOON_OOM_NOTIFY_PRIORITY
;
498 err
= register_oom_notifier(&vb
->nb
);
502 vb
->thread
= kthread_run(balloon
, vb
, "vballoon");
503 if (IS_ERR(vb
->thread
)) {
504 err
= PTR_ERR(vb
->thread
);
511 unregister_oom_notifier(&vb
->nb
);
513 vdev
->config
->del_vqs(vdev
);
520 static void remove_common(struct virtio_balloon
*vb
)
522 /* There might be pages left in the balloon: free them. */
523 while (vb
->num_pages
)
524 leak_balloon(vb
, vb
->num_pages
);
525 update_balloon_size(vb
);
527 /* Now we reset the device so we can clean up the queues. */
528 vb
->vdev
->config
->reset(vb
->vdev
);
530 vb
->vdev
->config
->del_vqs(vb
->vdev
);
533 static void virtballoon_remove(struct virtio_device
*vdev
)
535 struct virtio_balloon
*vb
= vdev
->priv
;
537 unregister_oom_notifier(&vb
->nb
);
538 kthread_stop(vb
->thread
);
543 #ifdef CONFIG_PM_SLEEP
544 static int virtballoon_freeze(struct virtio_device
*vdev
)
546 struct virtio_balloon
*vb
= vdev
->priv
;
549 * The kthread is already frozen by the PM core before this
550 * function is called.
557 static int virtballoon_restore(struct virtio_device
*vdev
)
559 struct virtio_balloon
*vb
= vdev
->priv
;
562 ret
= init_vqs(vdev
->priv
);
566 virtio_device_ready(vdev
);
568 fill_balloon(vb
, towards_target(vb
));
569 update_balloon_size(vb
);
574 static unsigned int features
[] = {
575 VIRTIO_BALLOON_F_MUST_TELL_HOST
,
576 VIRTIO_BALLOON_F_STATS_VQ
,
577 VIRTIO_BALLOON_F_DEFLATE_ON_OOM
,
580 static struct virtio_driver virtio_balloon_driver
= {
581 .feature_table
= features
,
582 .feature_table_size
= ARRAY_SIZE(features
),
583 .driver
.name
= KBUILD_MODNAME
,
584 .driver
.owner
= THIS_MODULE
,
585 .id_table
= id_table
,
586 .probe
= virtballoon_probe
,
587 .remove
= virtballoon_remove
,
588 .config_changed
= virtballoon_changed
,
589 #ifdef CONFIG_PM_SLEEP
590 .freeze
= virtballoon_freeze
,
591 .restore
= virtballoon_restore
,
595 module_virtio_driver(virtio_balloon_driver
);
596 MODULE_DEVICE_TABLE(virtio
, id_table
);
597 MODULE_DESCRIPTION("Virtio balloon driver");
598 MODULE_LICENSE("GPL");