Rusty Russell wrote:
> After discussions with Anthony Liguori, it seems that the virtio
> balloon can be made even simpler. Here's my attempt.
>
> Since the balloon requires Guest cooperation anyway, there seems
> little reason to force it to tell the Host when it wants to reuse a
> page. It can simply fault it in.
>
> Moreover, the target is best expressed in balloon size, since there is
> no portable way of getting the total RAM in the system. The host can
> do the math.
>
> Tested with a (fairly hacky) lguest patch.
>
> Signed-off-by: Rusty Russell <[EMAIL PROTECTED]>
> ---
> drivers/virtio/Kconfig | 10 +
> drivers/virtio/Makefile | 1
> drivers/virtio/virtio_balloon.c | 230
> ++++++++++++++++++++++++++++++++++++++++
> include/linux/virtio_balloon.h | 13 ++
> 4 files changed, 254 insertions(+)
>
> diff -r c4762959de25 drivers/virtio/Kconfig
> --- a/drivers/virtio/Kconfig Thu Jan 17 10:31:37 2008 +1100
> +++ b/drivers/virtio/Kconfig Thu Jan 17 12:28:23 2008 +1100
> @@ -23,3 +23,13 @@ config VIRTIO_PCI
>
> If unsure, say M.
>
> +config VIRTIO_BALLOON
> + tristate "Virtio balloon driver (EXPERIMENTAL)"
> + select VIRTIO
> + select VIRTIO_RING
> + ---help---
> + This driver supports increasing and decreasing the amount
> + of memory within a KVM guest.
> +
> + If unsure, say M.
> +
> diff -r c4762959de25 drivers/virtio/Makefile
> --- a/drivers/virtio/Makefile Thu Jan 17 10:31:37 2008 +1100
> +++ b/drivers/virtio/Makefile Thu Jan 17 12:28:23 2008 +1100
> @@ -1,3 +1,4 @@ obj-$(CONFIG_VIRTIO) += virtio.o
> obj-$(CONFIG_VIRTIO) += virtio.o
> obj-$(CONFIG_VIRTIO_RING) += virtio_ring.o
> obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
> +obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
> diff -r c4762959de25 drivers/virtio/virtio_balloon.c
> --- /dev/null Thu Jan 01 00:00:00 1970 +0000
> +++ b/drivers/virtio/virtio_balloon.c Thu Jan 17 12:28:23 2008 +1100
> @@ -0,0 +1,235 @@
> +/* Virtio balloon implementation, inspired by Dor Loar 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
> + */
> +#define DEBUG
> +#include <linux/virtio.h>
> +#include <linux/virtio_balloon.h>
> +#include <linux/swap.h>
> +#include <linux/kthread.h>
> +#include <linux/freezer.h>
> +
> +struct virtio_balloon
> +{
> + struct virtio_device *vdev;
> + struct virtqueue *vq;
> +
> + /* Where the ballooning thread waits for config to change. */
> + wait_queue_head_t config_change;
> +
> + /* The thread servicing the balloon. */
> + struct task_struct *thread;
> +
> + /* Waiting for host to ack the pages we released. */
> + struct completion acked;
> +
> + /* The pages we've told the Host we're not using. */
> + unsigned int num_pages;
> + struct list_head pages;
> +
> + /* The array of pfns we tell the Host about. */
> + unsigned int num_pfns;
> + u32 pfns[256];
> +};
> +
> +static struct virtio_device_id id_table[] = {
> + { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID},
>
Could use a space after VIRTIO_DEV_ANY_ID
> + { 0 },
> +};
> +
> +static void leak_balloon(struct virtio_balloon *vb, unsigned int num)
> +{
> + struct page *page;
> + unsigned int i;
> +
> + /* Simply free pages, and usage will fault them back in. */
> + for (i = 0; i < num; i++) {
> + page = list_first_entry(&vb->pages, struct page, lru);
> + list_del(&page->lru);
> + __free_page(page);
> + vb->num_pages--;
> + totalram_pages++;
>
Do we really want to modify totalram_pages in this driver? The only
other place that I see that modifies it is in mm/memory_hotplug and it
also modifies other things (like num_physpages). The cmm driver doesn't
touch totalram_pages.
It would be very useful too to write vb->num_pages into the config space
whenever it was updated. This way, the host can easily keep track of
where the guest is at in terms of ballooning.
Regards,
Anthony Liguori
> + }
> +}
> +
> +static void balloon_ack(struct virtqueue *vq)
> +{
> + struct virtio_balloon *vb;
> + unsigned int len;
> +
> + vb = vq->vq_ops->get_buf(vq, &len);
> + if (vb)
> + complete(&vb->acked);
> +}
> +
> +static void fill_balloon(struct virtio_balloon *vb, unsigned int num)
> +{
> + struct scatterlist sg;
> +
> + /* We can only do one array worth at a time. */
> + num = min(num, ARRAY_SIZE(vb->pfns));
> +
> + for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
> + struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
> + if (!page) {
> + if (printk_ratelimit())
> + dev_printk(KERN_INFO, &vb->vdev->dev,
> + "Out of puff! Can't get %u pages\n",
> + num);
> + /* Sleep for at least 1/5 of a second before retry. */
> + msleep(200);
> + break;
> + }
> + vb->pfns[vb->num_pfns] = page_to_pfn(page);
> + totalram_pages--;
> + vb->num_pages++;
> + list_add(&page->lru, &vb->pages);
> + }
> +
> + /* Didn't get any? Oh well. */
> + if (vb->num_pfns == 0)
> + return;
> +
> + init_completion(&vb->acked);
> + 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. */
> + if (vb->vq->vq_ops->add_buf(vb->vq, &sg, 1, 0, vb) != 0)
> + BUG();
> + vb->vq->vq_ops->kick(vb->vq);
> +
> + /* When host has read buffer, this completes via balloon_ack */
> + wait_for_completion(&vb->acked);
> +}
> +
> +static void virtballoon_changed(struct virtio_device *vdev)
> +{
> + struct virtio_balloon *vb = vdev->priv;
> +
> + wake_up(&vb->config_change);
> +}
> +
> +static inline int towards_target(struct virtio_balloon *vb)
> +{
> + u32 v;
> + __virtio_config_val(vb->vdev,
> + offsetof(struct virtio_balloon_config, num_pages),
> + &v);
> + return v - vb->num_pages;
> +}
> +
> +static int balloon(void *_vballoon)
> +{
> + struct virtio_balloon *vb = _vballoon;
> +
> + set_freezable();
> + while (!kthread_should_stop()) {
> + int diff;
> +
> + try_to_freeze();
> + wait_event_interruptible(vb->config_change,
> + (diff = towards_target(vb)) != 0
> + || kthread_should_stop());
> + if (diff > 0)
> + fill_balloon(vb, diff);
> + else if (diff < 0)
> + leak_balloon(vb, -diff);
> + }
> + return 0;
> +}
> +
> +static int virtballoon_probe(struct virtio_device *vdev)
> +{
> + struct virtio_balloon *vb;
> + int err;
> +
> + vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
> + if (!vb) {
> + err = -ENOMEM;
> + goto out;
> + }
> +
> + INIT_LIST_HEAD(&vb->pages);
> + vb->num_pages = 0;
> + init_waitqueue_head(&vb->config_change);
> + vb->vdev = vdev;
> +
> + /* We expect one virtqueue, for output. */
> + vb->vq = vdev->config->find_vq(vdev, 0, balloon_ack);
> + if (IS_ERR(vb->vq)) {
> + err = PTR_ERR(vb->vq);
> + goto out_free_vb;
> + }
> +
> + vb->thread = kthread_run(balloon, vb, "vballoon");
> + if (IS_ERR(vb->thread)) {
> + err = PTR_ERR(vb->thread);
> + goto out_del_vq;
> + }
> + return 0;
> +
> +out_del_vq:
> + vdev->config->del_vq(vb->vq);
> +out_free_vb:
> + kfree(vb);
> +out:
> + return err;
> +}
> +
> +static void virtballoon_remove(struct virtio_device *vdev)
> +{
> + struct virtio_balloon *vb = vdev->priv;
> + struct page *i, *next;
> +
> + kthread_stop(vb->thread);
> +
> + /* There might be pages left in the balloon: free them. */
> + list_for_each_entry_safe(i, next, &vb->pages, lru) {
> + vb->num_pages--;
> + __free_page(i);
> + }
> + BUG_ON(vb->num_pages);
> +
> + vdev->config->del_vq(vb->vq);
> + kfree(vb);
> +}
> +
> +static struct virtio_driver virtio_balloon = {
> + .driver.name = KBUILD_MODNAME,
> + .driver.owner = THIS_MODULE,
> + .id_table = id_table,
> + .probe = virtballoon_probe,
> + .remove = __devexit_p(virtballoon_remove),
> + .config_changed = virtballoon_changed,
> +};
> +
> +static int __init init(void)
> +{
> + return register_virtio_driver(&virtio_balloon);
> +}
> +
> +static void __exit fini(void)
> +{
> + unregister_virtio_driver(&virtio_balloon);
> +}
> +module_init(init);
> +module_exit(fini);
> +
> +MODULE_DEVICE_TABLE(virtio, id_table);
> +MODULE_DESCRIPTION("Virtio balloon driver");
> +MODULE_LICENSE("GPL");
> diff -r c4762959de25 include/linux/virtio_balloon.h
> --- /dev/null Thu Jan 01 00:00:00 1970 +0000
> +++ b/include/linux/virtio_balloon.h Thu Jan 17 12:28:23 2008 +1100
> @@ -0,0 +1,13 @@
> +#ifndef _LINUX_VIRTIO_BALLOON_H
> +#define _LINUX_VIRTIO_BALLOON_H
> +#include <linux/virtio_config.h>
> +
> +/* The ID for virtio_balloon */
> +#define VIRTIO_ID_BALLOON 5
> +
> +struct virtio_balloon_config
> +{
> + /* Number of pages host wants Guest to give up. */
> + __le32 num_pages;
> +};
> +#endif /* _LINUX_VIRTIO_BALLOON_H */
>
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