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/workqueue.h>
26 #include <linux/delay.h>
27 #include <linux/slab.h>
28 #include <linux/module.h>
29 #include <linux/balloon_compaction.h>
30 #include <linux/oom.h>
31 #include <linux/wait.h>
35 * Balloon device works in 4K page units. So each page is pointed to by
36 * multiple balloon pages. All memory counters in this driver are in balloon
39 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
40 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
41 #define OOM_VBALLOON_DEFAULT_PAGES 256
42 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
44 static int oom_pages
= OOM_VBALLOON_DEFAULT_PAGES
;
45 module_param(oom_pages
, int, S_IRUSR
| S_IWUSR
);
46 MODULE_PARM_DESC(oom_pages
, "pages to free on OOM");
48 struct virtio_balloon
{
49 struct virtio_device
*vdev
;
50 struct virtqueue
*inflate_vq
, *deflate_vq
, *stats_vq
;
52 /* The balloon servicing is delegated to a freezable workqueue. */
53 struct work_struct update_balloon_stats_work
;
54 struct work_struct update_balloon_size_work
;
56 /* Prevent updating balloon when it is being canceled. */
57 spinlock_t stop_update_lock
;
60 /* Waiting for host to ack the pages we released. */
61 wait_queue_head_t acked
;
63 /* Number of balloon pages we've told the Host we're not using. */
64 unsigned int num_pages
;
66 * The pages we've told the Host we're not using are enqueued
67 * at vb_dev_info->pages list.
68 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
71 struct balloon_dev_info vb_dev_info
;
73 /* Synchronize access/update to this struct virtio_balloon elements */
74 struct mutex balloon_lock
;
76 /* The array of pfns we tell the Host about. */
77 unsigned int num_pfns
;
78 __virtio32 pfns
[VIRTIO_BALLOON_ARRAY_PFNS_MAX
];
80 /* Memory statistics */
81 struct virtio_balloon_stat stats
[VIRTIO_BALLOON_S_NR
];
83 /* To register callback in oom notifier call chain */
84 struct notifier_block nb
;
87 static struct virtio_device_id id_table
[] = {
88 { VIRTIO_ID_BALLOON
, VIRTIO_DEV_ANY_ID
},
92 static u32
page_to_balloon_pfn(struct page
*page
)
94 unsigned long pfn
= page_to_pfn(page
);
96 BUILD_BUG_ON(PAGE_SHIFT
< VIRTIO_BALLOON_PFN_SHIFT
);
97 /* Convert pfn from Linux page size to balloon page size. */
98 return pfn
* VIRTIO_BALLOON_PAGES_PER_PAGE
;
101 static struct page
*balloon_pfn_to_page(u32 pfn
)
103 BUG_ON(pfn
% VIRTIO_BALLOON_PAGES_PER_PAGE
);
104 return pfn_to_page(pfn
/ VIRTIO_BALLOON_PAGES_PER_PAGE
);
107 static void balloon_ack(struct virtqueue
*vq
)
109 struct virtio_balloon
*vb
= vq
->vdev
->priv
;
114 static void tell_host(struct virtio_balloon
*vb
, struct virtqueue
*vq
)
116 struct scatterlist sg
;
119 sg_init_one(&sg
, vb
->pfns
, sizeof(vb
->pfns
[0]) * vb
->num_pfns
);
121 /* We should always be able to add one buffer to an empty queue. */
122 virtqueue_add_outbuf(vq
, &sg
, 1, vb
, GFP_KERNEL
);
125 /* When host has read buffer, this completes via balloon_ack */
126 wait_event(vb
->acked
, virtqueue_get_buf(vq
, &len
));
130 static void set_page_pfns(struct virtio_balloon
*vb
,
131 __virtio32 pfns
[], struct page
*page
)
135 /* Set balloon pfns pointing at this page.
136 * Note that the first pfn points at start of the page. */
137 for (i
= 0; i
< VIRTIO_BALLOON_PAGES_PER_PAGE
; i
++)
138 pfns
[i
] = cpu_to_virtio32(vb
->vdev
,
139 page_to_balloon_pfn(page
) + i
);
142 static unsigned fill_balloon(struct virtio_balloon
*vb
, size_t num
)
144 struct balloon_dev_info
*vb_dev_info
= &vb
->vb_dev_info
;
145 unsigned num_allocated_pages
;
147 /* We can only do one array worth at a time. */
148 num
= min(num
, ARRAY_SIZE(vb
->pfns
));
150 mutex_lock(&vb
->balloon_lock
);
151 for (vb
->num_pfns
= 0; vb
->num_pfns
< num
;
152 vb
->num_pfns
+= VIRTIO_BALLOON_PAGES_PER_PAGE
) {
153 struct page
*page
= balloon_page_enqueue(vb_dev_info
);
156 dev_info_ratelimited(&vb
->vdev
->dev
,
157 "Out of puff! Can't get %u pages\n",
158 VIRTIO_BALLOON_PAGES_PER_PAGE
);
159 /* Sleep for at least 1/5 of a second before retry. */
163 set_page_pfns(vb
, vb
->pfns
+ vb
->num_pfns
, page
);
164 vb
->num_pages
+= VIRTIO_BALLOON_PAGES_PER_PAGE
;
165 if (!virtio_has_feature(vb
->vdev
,
166 VIRTIO_BALLOON_F_DEFLATE_ON_OOM
))
167 adjust_managed_page_count(page
, -1);
170 num_allocated_pages
= vb
->num_pfns
;
171 /* Did we get any? */
172 if (vb
->num_pfns
!= 0)
173 tell_host(vb
, vb
->inflate_vq
);
174 mutex_unlock(&vb
->balloon_lock
);
176 return num_allocated_pages
;
179 static void release_pages_balloon(struct virtio_balloon
*vb
)
184 /* Find pfns pointing at start of each page, get pages and free them. */
185 for (i
= 0; i
< vb
->num_pfns
; i
+= VIRTIO_BALLOON_PAGES_PER_PAGE
) {
186 page
= balloon_pfn_to_page(virtio32_to_cpu(vb
->vdev
,
188 if (!virtio_has_feature(vb
->vdev
,
189 VIRTIO_BALLOON_F_DEFLATE_ON_OOM
))
190 adjust_managed_page_count(page
, 1);
191 put_page(page
); /* balloon reference */
195 static unsigned leak_balloon(struct virtio_balloon
*vb
, size_t num
)
197 unsigned num_freed_pages
;
199 struct balloon_dev_info
*vb_dev_info
= &vb
->vb_dev_info
;
201 /* We can only do one array worth at a time. */
202 num
= min(num
, ARRAY_SIZE(vb
->pfns
));
204 mutex_lock(&vb
->balloon_lock
);
205 for (vb
->num_pfns
= 0; vb
->num_pfns
< num
;
206 vb
->num_pfns
+= VIRTIO_BALLOON_PAGES_PER_PAGE
) {
207 page
= balloon_page_dequeue(vb_dev_info
);
210 set_page_pfns(vb
, vb
->pfns
+ vb
->num_pfns
, page
);
211 vb
->num_pages
-= VIRTIO_BALLOON_PAGES_PER_PAGE
;
214 num_freed_pages
= vb
->num_pfns
;
217 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
218 * is true, we *have* to do it in this order
220 if (vb
->num_pfns
!= 0)
221 tell_host(vb
, vb
->deflate_vq
);
222 release_pages_balloon(vb
);
223 mutex_unlock(&vb
->balloon_lock
);
224 return num_freed_pages
;
227 static inline void update_stat(struct virtio_balloon
*vb
, int idx
,
230 BUG_ON(idx
>= VIRTIO_BALLOON_S_NR
);
231 vb
->stats
[idx
].tag
= cpu_to_virtio16(vb
->vdev
, tag
);
232 vb
->stats
[idx
].val
= cpu_to_virtio64(vb
->vdev
, val
);
235 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
237 static void update_balloon_stats(struct virtio_balloon
*vb
)
239 unsigned long events
[NR_VM_EVENT_ITEMS
];
244 all_vm_events(events
);
247 available
= si_mem_available();
249 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_SWAP_IN
,
250 pages_to_bytes(events
[PSWPIN
]));
251 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_SWAP_OUT
,
252 pages_to_bytes(events
[PSWPOUT
]));
253 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MAJFLT
, events
[PGMAJFAULT
]);
254 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MINFLT
, events
[PGFAULT
]);
255 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MEMFREE
,
256 pages_to_bytes(i
.freeram
));
257 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_MEMTOT
,
258 pages_to_bytes(i
.totalram
));
259 update_stat(vb
, idx
++, VIRTIO_BALLOON_S_AVAIL
,
260 pages_to_bytes(available
));
264 * While most virtqueues communicate guest-initiated requests to the hypervisor,
265 * the stats queue operates in reverse. The driver initializes the virtqueue
266 * with a single buffer. From that point forward, all conversations consist of
267 * a hypervisor request (a call to this function) which directs us to refill
268 * the virtqueue with a fresh stats buffer. Since stats collection can sleep,
269 * we delegate the job to a freezable workqueue that will do the actual work via
270 * stats_handle_request().
272 static void stats_request(struct virtqueue
*vq
)
274 struct virtio_balloon
*vb
= vq
->vdev
->priv
;
276 spin_lock(&vb
->stop_update_lock
);
277 if (!vb
->stop_update
)
278 queue_work(system_freezable_wq
, &vb
->update_balloon_stats_work
);
279 spin_unlock(&vb
->stop_update_lock
);
282 static void stats_handle_request(struct virtio_balloon
*vb
)
284 struct virtqueue
*vq
;
285 struct scatterlist sg
;
288 update_balloon_stats(vb
);
291 if (!virtqueue_get_buf(vq
, &len
))
293 sg_init_one(&sg
, vb
->stats
, sizeof(vb
->stats
));
294 virtqueue_add_outbuf(vq
, &sg
, 1, vb
, GFP_KERNEL
);
298 static void virtballoon_changed(struct virtio_device
*vdev
)
300 struct virtio_balloon
*vb
= vdev
->priv
;
303 spin_lock_irqsave(&vb
->stop_update_lock
, flags
);
304 if (!vb
->stop_update
)
305 queue_work(system_freezable_wq
, &vb
->update_balloon_size_work
);
306 spin_unlock_irqrestore(&vb
->stop_update_lock
, flags
);
309 static inline s64
towards_target(struct virtio_balloon
*vb
)
314 virtio_cread(vb
->vdev
, struct virtio_balloon_config
, num_pages
,
317 /* Legacy balloon config space is LE, unlike all other devices. */
318 if (!virtio_has_feature(vb
->vdev
, VIRTIO_F_VERSION_1
))
319 num_pages
= le32_to_cpu((__force __le32
)num_pages
);
322 return target
- vb
->num_pages
;
325 static void update_balloon_size(struct virtio_balloon
*vb
)
327 u32 actual
= vb
->num_pages
;
329 /* Legacy balloon config space is LE, unlike all other devices. */
330 if (!virtio_has_feature(vb
->vdev
, VIRTIO_F_VERSION_1
))
331 actual
= (__force u32
)cpu_to_le32(actual
);
333 virtio_cwrite(vb
->vdev
, struct virtio_balloon_config
, actual
,
338 * virtballoon_oom_notify - release pages when system is under severe
339 * memory pressure (called from out_of_memory())
340 * @self : notifier block struct
342 * @parm : returned - number of freed pages
344 * The balancing of memory by use of the virtio balloon should not cause
345 * the termination of processes while there are pages in the balloon.
346 * If virtio balloon manages to release some memory, it will make the
347 * system return and retry the allocation that forced the OOM killer
350 static int virtballoon_oom_notify(struct notifier_block
*self
,
351 unsigned long dummy
, void *parm
)
353 struct virtio_balloon
*vb
;
354 unsigned long *freed
;
355 unsigned num_freed_pages
;
357 vb
= container_of(self
, struct virtio_balloon
, nb
);
358 if (!virtio_has_feature(vb
->vdev
, VIRTIO_BALLOON_F_DEFLATE_ON_OOM
))
362 num_freed_pages
= leak_balloon(vb
, oom_pages
);
363 update_balloon_size(vb
);
364 *freed
+= num_freed_pages
;
369 static void update_balloon_stats_func(struct work_struct
*work
)
371 struct virtio_balloon
*vb
;
373 vb
= container_of(work
, struct virtio_balloon
,
374 update_balloon_stats_work
);
375 stats_handle_request(vb
);
378 static void update_balloon_size_func(struct work_struct
*work
)
380 struct virtio_balloon
*vb
;
383 vb
= container_of(work
, struct virtio_balloon
,
384 update_balloon_size_work
);
385 diff
= towards_target(vb
);
388 diff
-= fill_balloon(vb
, diff
);
390 diff
+= leak_balloon(vb
, -diff
);
391 update_balloon_size(vb
);
394 queue_work(system_freezable_wq
, work
);
397 static int init_vqs(struct virtio_balloon
*vb
)
399 struct virtqueue
*vqs
[3];
400 vq_callback_t
*callbacks
[] = { balloon_ack
, balloon_ack
, stats_request
};
401 static const char * const names
[] = { "inflate", "deflate", "stats" };
405 * We expect two virtqueues: inflate and deflate, and
408 nvqs
= virtio_has_feature(vb
->vdev
, VIRTIO_BALLOON_F_STATS_VQ
) ? 3 : 2;
409 err
= vb
->vdev
->config
->find_vqs(vb
->vdev
, nvqs
, vqs
, callbacks
, names
);
413 vb
->inflate_vq
= vqs
[0];
414 vb
->deflate_vq
= vqs
[1];
415 if (virtio_has_feature(vb
->vdev
, VIRTIO_BALLOON_F_STATS_VQ
)) {
416 struct scatterlist sg
;
417 vb
->stats_vq
= vqs
[2];
420 * Prime this virtqueue with one buffer so the hypervisor can
421 * use it to signal us later (it can't be broken yet!).
423 sg_init_one(&sg
, vb
->stats
, sizeof vb
->stats
);
424 if (virtqueue_add_outbuf(vb
->stats_vq
, &sg
, 1, vb
, GFP_KERNEL
)
427 virtqueue_kick(vb
->stats_vq
);
432 #ifdef CONFIG_BALLOON_COMPACTION
434 * virtballoon_migratepage - perform the balloon page migration on behalf of
435 * a compation thread. (called under page lock)
436 * @vb_dev_info: the balloon device
437 * @newpage: page that will replace the isolated page after migration finishes.
438 * @page : the isolated (old) page that is about to be migrated to newpage.
439 * @mode : compaction mode -- not used for balloon page migration.
441 * After a ballooned page gets isolated by compaction procedures, this is the
442 * function that performs the page migration on behalf of a compaction thread
443 * The page migration for virtio balloon is done in a simple swap fashion which
444 * follows these two macro steps:
445 * 1) insert newpage into vb->pages list and update the host about it;
446 * 2) update the host about the old page removed from vb->pages list;
448 * This function preforms the balloon page migration task.
449 * Called through balloon_mapping->a_ops->migratepage
451 static int virtballoon_migratepage(struct balloon_dev_info
*vb_dev_info
,
452 struct page
*newpage
, struct page
*page
, enum migrate_mode mode
)
454 struct virtio_balloon
*vb
= container_of(vb_dev_info
,
455 struct virtio_balloon
, vb_dev_info
);
459 * In order to avoid lock contention while migrating pages concurrently
460 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
461 * this turn, as it is easier to retry the page migration later.
462 * This also prevents fill_balloon() getting stuck into a mutex
463 * recursion in the case it ends up triggering memory compaction
464 * while it is attempting to inflate the ballon.
466 if (!mutex_trylock(&vb
->balloon_lock
))
469 get_page(newpage
); /* balloon reference */
471 /* balloon's page migration 1st step -- inflate "newpage" */
472 spin_lock_irqsave(&vb_dev_info
->pages_lock
, flags
);
473 balloon_page_insert(vb_dev_info
, newpage
);
474 vb_dev_info
->isolated_pages
--;
475 __count_vm_event(BALLOON_MIGRATE
);
476 spin_unlock_irqrestore(&vb_dev_info
->pages_lock
, flags
);
477 vb
->num_pfns
= VIRTIO_BALLOON_PAGES_PER_PAGE
;
478 set_page_pfns(vb
, vb
->pfns
, newpage
);
479 tell_host(vb
, vb
->inflate_vq
);
481 /* balloon's page migration 2nd step -- deflate "page" */
482 balloon_page_delete(page
);
483 vb
->num_pfns
= VIRTIO_BALLOON_PAGES_PER_PAGE
;
484 set_page_pfns(vb
, vb
->pfns
, page
);
485 tell_host(vb
, vb
->deflate_vq
);
487 mutex_unlock(&vb
->balloon_lock
);
489 put_page(page
); /* balloon reference */
491 return MIGRATEPAGE_SUCCESS
;
493 #endif /* CONFIG_BALLOON_COMPACTION */
495 static int virtballoon_probe(struct virtio_device
*vdev
)
497 struct virtio_balloon
*vb
;
500 if (!vdev
->config
->get
) {
501 dev_err(&vdev
->dev
, "%s failure: config access disabled\n",
506 vdev
->priv
= vb
= kmalloc(sizeof(*vb
), GFP_KERNEL
);
512 INIT_WORK(&vb
->update_balloon_stats_work
, update_balloon_stats_func
);
513 INIT_WORK(&vb
->update_balloon_size_work
, update_balloon_size_func
);
514 spin_lock_init(&vb
->stop_update_lock
);
515 vb
->stop_update
= false;
517 mutex_init(&vb
->balloon_lock
);
518 init_waitqueue_head(&vb
->acked
);
521 balloon_devinfo_init(&vb
->vb_dev_info
);
522 #ifdef CONFIG_BALLOON_COMPACTION
523 vb
->vb_dev_info
.migratepage
= virtballoon_migratepage
;
530 vb
->nb
.notifier_call
= virtballoon_oom_notify
;
531 vb
->nb
.priority
= VIRTBALLOON_OOM_NOTIFY_PRIORITY
;
532 err
= register_oom_notifier(&vb
->nb
);
536 virtio_device_ready(vdev
);
541 vdev
->config
->del_vqs(vdev
);
548 static void remove_common(struct virtio_balloon
*vb
)
550 /* There might be pages left in the balloon: free them. */
551 while (vb
->num_pages
)
552 leak_balloon(vb
, vb
->num_pages
);
553 update_balloon_size(vb
);
555 /* Now we reset the device so we can clean up the queues. */
556 vb
->vdev
->config
->reset(vb
->vdev
);
558 vb
->vdev
->config
->del_vqs(vb
->vdev
);
561 static void virtballoon_remove(struct virtio_device
*vdev
)
563 struct virtio_balloon
*vb
= vdev
->priv
;
565 unregister_oom_notifier(&vb
->nb
);
567 spin_lock_irq(&vb
->stop_update_lock
);
568 vb
->stop_update
= true;
569 spin_unlock_irq(&vb
->stop_update_lock
);
570 cancel_work_sync(&vb
->update_balloon_size_work
);
571 cancel_work_sync(&vb
->update_balloon_stats_work
);
577 #ifdef CONFIG_PM_SLEEP
578 static int virtballoon_freeze(struct virtio_device
*vdev
)
580 struct virtio_balloon
*vb
= vdev
->priv
;
583 * The workqueue is already frozen by the PM core before this
584 * function is called.
590 static int virtballoon_restore(struct virtio_device
*vdev
)
592 struct virtio_balloon
*vb
= vdev
->priv
;
595 ret
= init_vqs(vdev
->priv
);
599 virtio_device_ready(vdev
);
601 if (towards_target(vb
))
602 virtballoon_changed(vdev
);
603 update_balloon_size(vb
);
608 static unsigned int features
[] = {
609 VIRTIO_BALLOON_F_MUST_TELL_HOST
,
610 VIRTIO_BALLOON_F_STATS_VQ
,
611 VIRTIO_BALLOON_F_DEFLATE_ON_OOM
,
614 static struct virtio_driver virtio_balloon_driver
= {
615 .feature_table
= features
,
616 .feature_table_size
= ARRAY_SIZE(features
),
617 .driver
.name
= KBUILD_MODNAME
,
618 .driver
.owner
= THIS_MODULE
,
619 .id_table
= id_table
,
620 .probe
= virtballoon_probe
,
621 .remove
= virtballoon_remove
,
622 .config_changed
= virtballoon_changed
,
623 #ifdef CONFIG_PM_SLEEP
624 .freeze
= virtballoon_freeze
,
625 .restore
= virtballoon_restore
,
629 module_virtio_driver(virtio_balloon_driver
);
630 MODULE_DEVICE_TABLE(virtio
, id_table
);
631 MODULE_DESCRIPTION("Virtio balloon driver");
632 MODULE_LICENSE("GPL");