On Tue, Jan 15, 2008 at 10:32:08AM +1100, Rusty Russell wrote:
> On Tuesday 15 January 2008 07:03:57 Marcelo Tosatti wrote:
> > Hi Rusty,
> >
> > It was agreed that the balloon driver should be merged through the
> > virtio tree, so here it goes. It depends on the config_changed patch
> > posted earlier.
>
> Hi Marcelo,
>
> Excellent! Although the main user will be kvm, it'd be nice to have a
> demonstration in-tree using lguest; any chance of you conjuring up an
> appropriate patch?
>
> If not, I can whip something up.
>
> > +config KVM_BALLOON
> > + tristate "KVM balloon driver (EXPERIMENTAL)"
> > + depends on VIRTIO_PCI
> > + ---help---
> > + This driver provides support for ballooning memory in/out of a
> > + KVM paravirt guest.
> > +
> > + If unsure, say M.
>
> Please don't define "balloon" in terms of "ballooning". How about "This
> driver supports increasing and decreasing the amount of memory within a KVM
> guest." ?
>
> > + uint32_t target_nrpages;
>
> I prefer u32 within the kernel, but no big deal.
>
> > +static int send_balloon_buf(struct virtballoon *v, uint8_t cmd,
> > + struct balloon_buf *buf)
> > +{
> > + struct scatterlist sg[VIRTIO_MAX_SG];
> > + int err = 0;
> > +
> > + buf->hdr.cmd = cmd;
> > +
> > + sg_init_table(sg, VIRTIO_MAX_SG);
> > + sg_set_buf(&sg[0], &buf->hdr, sizeof(buf->hdr));
> > + sg_set_buf(&sg[1], &buf->data, sizeof(buf->data));
>
> Since these are adjacent, can't you just combine them into one sg element? Or
> does the kvm code rely on the sg as a boundary between header and data?
>
> > +static int kvm_balloon_inflate(struct virtballoon *v, int32_t npages)
> > +{
> > + LIST_HEAD(tmp_list);
> > + struct page *page, *tmp;
> > + struct balloon_buf *buf;
> > + u32 *pfn;
> > + int allocated = 0;
> > + int i, r = -ENOMEM;
> > +
> > + buf = alloc_balloon_buf(v->vdev, GFP_KERNEL);
> > + if (!buf)
> > + return r;
> > +
> > + pfn = (u32 *)&buf->data;
> > + *pfn++ = (u32)npages;
>
> OK, this seems strange. You always use the data portion as an array of u32s,
> yet you declare it as char[200]. You have a perfectly good header, but you
> put the number of pages in the first element of the data array: and you hand
> the entire data array even though you normally only use part of it.
>
> You can intuit the number from the sg len, I suggest you do that instead.
>
> Looking at this driver, I just don't think this needs to be so complicated:
> it's not a high speed device, after all. Perhaps allocate one buffer up
> front, and just reuse that. One simple thread loop, less locking needed.
>
> > + for (i = 0; i < npages; i++) {
> > + page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
> > + if (!page)
> > + goto out_free;
> > + list_add(&page->lru, &tmp_list);
> > + allocated++;
> > + *pfn = page_to_pfn(page);
> > + pfn++;
> > + }
>
> I think it might be simpler to defer adding to any list until after the
> callback is done? Helpers to add an array to the balloon array (on
> successful inflate, or unsuccessful deflate) and to free them (unsuccessful
> inflate, or successful deflate) would also make the code more readable.
>
> > + gfns_per_buf = MAX_BALLOON_PAGES_PER_OP;
> > +
> > + /*
> > + * Call the balloon in PAGE_SIZE*pfns-per-buf
> > + * iterations
> > + */
> > + iterations = DIV_ROUND_UP(abspages, gfns_per_buf);
> > + dprintk(&v->vdev->dev, "%s: iterations=%d\n", __func__, iterations);
> > +
> > + for (i = 0; i < iterations; i++) {
>
> This logic seems overly complex. How about in the main thread:
>
> /* We're woken when target changes, in config_changed() */
> if (wait_event_interruptible(&v->wq,
> (diff = atomic_read(&v->target_pages) - total_pages)) == 0) {
>
> /* If we submit inflate/deflate request, wait for it to finish. */
> if (xflate(v, diff) == 0)
> wait_for_completion(&v->complete);
> }
>
> xflate just does as much as it can (up to "diff"), and then the interrupt
> handler adds/removes from the linked list, frees pages, etc and fires the
> completion.
>
> No need for locking, since there's only one pending request at any time.
OK, thats simpler. How about this:
[PATCH] Virtio balloon driver
Add a balloon driver for KVM, host<->guest communication is performed
via virtio.
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Index: linux-2.6-nv/drivers/virtio/Kconfig
===================================================================
--- linux-2.6-nv.orig/drivers/virtio/Kconfig
+++ linux-2.6-nv/drivers/virtio/Kconfig
@@ -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.
+
Index: linux-2.6-nv/drivers/virtio/Makefile
===================================================================
--- linux-2.6-nv.orig/drivers/virtio/Makefile
+++ linux-2.6-nv/drivers/virtio/Makefile
@@ -1,3 +1,4 @@
obj-$(CONFIG_VIRTIO) += virtio.o
obj-$(CONFIG_VIRTIO_RING) += virtio_ring.o
obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
+obj-$(CONFIG_VIRTIO_BALLOON) += kvm_balloon.o
Index: linux-2.6-nv/drivers/virtio/kvm_balloon.c
===================================================================
--- /dev/null
+++ linux-2.6-nv/drivers/virtio/kvm_balloon.c
@@ -0,0 +1,404 @@
+/*
+ * KVM guest balloon driver
+ *
+ * Copyright (C) 2007, Qumranet, Inc., Dor Laor <dor.laor@xxxxxxxxxxxx>
+ * Copyright (C) 2007, Red Hat, Inc., Marcelo Tosatti <mtosatti@xxxxxxxxxx>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ */
+
+#define DEBUG
+#include <asm/uaccess.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/wait.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/version.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_balloon.h>
+#include <linux/preempt.h>
+
+MODULE_AUTHOR ("Dor Laor");
+MODULE_DESCRIPTION ("Implements guest ballooning support");
+MODULE_LICENSE("GPL");
+MODULE_VERSION("1");
+
+static int kvm_balloon_debug;
+
+#define dprintk(dev, str...) if (kvm_balloon_debug) dev_dbg(dev, str)
+
+#define BALLOON_DATA_SIZE 200
+
+struct balloon_buf {
+ struct virtio_balloon_hdr hdr;
+ u8 data[BALLOON_DATA_SIZE];
+};
+
+#define VIRTIO_MAX_SG 2
+
+struct virtballoon {
+ struct virtio_device *vdev;
+ struct virtqueue *vq;
+ struct task_struct *balloon_thread;
+ struct balloon_buf buf;
+ wait_queue_head_t balloon_wait;
+ wait_queue_head_t rmmod_wait;
+ struct completion complete;
+ atomic_t target_nrpages;
+ int balloon_size;
+ struct list_head balloon_plist;
+ struct list_head list;
+};
+
+
+static int send_balloon_buf(struct virtballoon *v, u8 cmd,
+ struct balloon_buf *buf, unsigned int data_len)
+{
+ struct scatterlist sg[VIRTIO_MAX_SG];
+ int err = 0;
+
+ buf->hdr.cmd = cmd;
+
+ sg_init_table(sg, VIRTIO_MAX_SG);
+ sg_set_buf(&sg[0], &buf->hdr, sizeof(buf->hdr));
+ sg_set_buf(&sg[1], &buf->data, data_len);
+
+ err = v->vq->vq_ops->add_buf(v->vq, sg, 0, 2, buf);
+ if (err) {
+ dev_printk(KERN_ERR, &v->vq->vdev->dev, "%s: add_buf err\n",
+ __func__);
+ goto out;
+ }
+
+ v->vq->vq_ops->kick(v->vq);
+out:
+ return err;
+}
+
+static int kvm_balloon_inflate(struct virtballoon *v, int32_t npages)
+{
+ struct page *page;
+ struct balloon_buf *buf = &v->buf;
+ u32 *pfn;
+ int allocated = 0;
+ int i, r = -ENOMEM;
+
+ pfn = (u32 *)&buf->data;
+ for (i = 0; i < npages; i++) {
+ page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
+ if (!page)
+ goto out_free;
+ allocated++;
+ *pfn = page_to_pfn(page);
+ pfn++;
+ }
+
+ r = send_balloon_buf(v, CMD_BALLOON_INFLATE, buf,
+ allocated * sizeof(u32));
+ if (r)
+ goto out_free;
+
+ dprintk(&v->vdev->dev, "%s: current balloon size=%d\n", __func__,
+ v->balloon_size);
+ return r;
+
+out_free:
+ pfn = (u32 *)&buf->data;
+ for (i = 0; i < allocated; i++)
+ __free_page(pfn_to_page(*pfn++));
+ return r;
+}
+
+static int kvm_balloon_deflate(struct virtballoon *v, int32_t npages)
+{
+ struct page *page;
+ struct balloon_buf *buf = &v->buf;
+ u32 *pfn;
+ int deallocated = 0;
+ int r = 0;
+
+ if (v->balloon_size < npages) {
+ dev_printk(KERN_INFO, &v->vdev->dev,
+ "%s: balloon=%d with deflate rq=%d\n",
+ __func__, v->balloon_size, npages);
+ npages = v->balloon_size;
+ if (!npages) {
+ r = -EINVAL;
+ goto out;
+ }
+ }
+
+ dprintk(&v->vdev->dev, "%s: current balloon size=%d\n", __func__,
+ v->balloon_size);
+
+ pfn = (u32 *)&buf->data;
+
+ list_for_each_entry(page, &v->balloon_plist, lru) {
+ *pfn++ = page_to_pfn(page);
+ if (++deallocated == npages)
+ break;
+ }
+
+ r = send_balloon_buf(v, CMD_BALLOON_DEFLATE, buf,
+ deallocated * sizeof(u32));
+out:
+ return r;
+}
+
+#define MAX_BALLOON_PAGES_PER_OP (BALLOON_DATA_SIZE/sizeof(u32))
+#define MAX_BALLOON_XFLATE_OP 1000000
+
+static int kvm_balloon_xflate(struct virtballoon *v, int32_t npages)
+{
+ int r = -EINVAL;
+ int pages_in_iteration;
+ int abspages;
+ int maxpages = MAX_BALLOON_PAGES_PER_OP;
+
+ abspages = abs(npages);
+
+ if (abspages > MAX_BALLOON_XFLATE_OP) {
+ dev_printk(KERN_ERR, &v->vdev->dev,
+ "%s: bad npages=%d\n", __func__, npages);
+ goto out;
+ }
+
+ dprintk(&v->vdev->dev, "%s: got %s, npages=%d\n", __func__,
+ (npages > 0)? "inflate":"deflate", npages);
+
+ pages_in_iteration = min(maxpages, abspages);
+
+ if (npages > 0)
+ r = kvm_balloon_inflate(v, pages_in_iteration);
+ else
+ r = kvm_balloon_deflate(v, pages_in_iteration);
+
+out:
+ /* stop the thread in case of an error */
+ if (r)
+ atomic_set(&v->target_nrpages, totalram_pages);
+ return r;
+}
+
+static void free_page_array(struct balloon_buf *buf, unsigned int npages)
+{
+ struct page *page;
+ u32 *pfn = (u32 *)&buf->data;
+ int i;
+
+ for (i=0; i<npages; i++) {
+ page = pfn_to_page(*pfn);
+ list_del_init(&page->lru);
+ __free_page(page);
+ pfn++;
+ }
+}
+
+static void add_page_array(struct virtballoon *v, struct balloon_buf *buf,
+ unsigned int npages)
+{
+ struct page *page;
+ u32 *pfn = (u32 *)&buf->data;
+ int i;
+
+ for (i=0; i<npages; i++) {
+ page = pfn_to_page(*pfn);
+ v->balloon_size++;
+ totalram_pages--;
+ list_add(&page->lru, &v->balloon_plist);
+ pfn++;
+ }
+}
+
+static void inflate_done(struct virtballoon *v, struct balloon_buf *buf,
+ unsigned int npages)
+{
+ u8 status = buf->hdr.status;
+
+ /* inflate OK */
+ if (!status)
+ add_page_array(v, buf, npages);
+ else
+ free_page_array(buf, npages);
+}
+
+static void deflate_done(struct virtballoon *v, struct balloon_buf *buf,
+ unsigned int npages)
+{
+ u8 status = buf->hdr.status;
+
+ /* deflate OK, return pages to the system */
+ if (!status) {
+ free_page_array(buf, npages);
+ totalram_pages += npages;
+ v->balloon_size -= npages;
+ }
+ return;
+}
+
+static int balloon_thread(void *p)
+{
+ struct virtballoon *v = p;
+ DEFINE_WAIT(wait);
+
+ set_freezable();
+ while (!kthread_should_stop()) {
+ int diff, r;
+
+ try_to_freeze();
+
+ r = wait_event_interruptible(v->balloon_wait,
+ (diff = totalram_pages -
+ atomic_read(&v->target_nrpages))
+ || kthread_should_stop());
+ if (r == 0)
+ if (kvm_balloon_xflate(v, diff) == 0)
+ wait_for_completion(&v->complete);
+
+ if (waitqueue_active(&v->rmmod_wait)) {
+ diff = totalram_pages - atomic_read(&v->target_nrpages);
+ if (!diff)
+ wake_up(&v->rmmod_wait);
+ }
+ }
+ return 0;
+}
+
+static bool balloon_tx_done(struct virtqueue *vq)
+{
+ struct balloon_buf *buf;
+ struct virtballoon *v = vq->vdev->priv;
+ unsigned int len;
+
+ buf = vq->vq_ops->get_buf(vq, &len);
+ if (buf) {
+ switch(buf->hdr.cmd) {
+ case CMD_BALLOON_DEFLATE:
+ deflate_done(v, buf, len/sizeof(u32));
+ break;
+ case CMD_BALLOON_INFLATE:
+ inflate_done(v, buf, len/sizeof(u32));
+ break;
+ default:
+ printk("%s: unknown cmd 0x%x\n", __func__,
+ buf->hdr.cmd);
+ }
+ complete(&v->complete);
+ }
+ return true;
+}
+
+static struct virtio_device_id id_table[] = {
+ { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID},
+ { 0 },
+};
+
+static LIST_HEAD(balloon_devices);
+
+static int balloon_probe(struct virtio_device *vdev)
+{
+ int err = -EINVAL;
+ struct virtballoon *v;
+
+ v = kzalloc(GFP_KERNEL, sizeof(struct virtballoon));
+ if (!v)
+ return -ENOMEM;
+
+ v->vq = vdev->config->find_vq(vdev, 0, balloon_tx_done);
+ if (IS_ERR(v->vq))
+ goto out_free;
+
+ v->vdev = vdev;
+
+ init_waitqueue_head(&v->balloon_wait);
+ init_waitqueue_head(&v->rmmod_wait);
+ INIT_LIST_HEAD(&v->balloon_plist);
+ INIT_LIST_HEAD(&v->list);
+ init_completion(&v->complete);
+ atomic_set(&v->target_nrpages, totalram_pages);
+
+ vdev->priv = v;
+
+ v->balloon_thread = kthread_run(balloon_thread, v, "kvm_balloond");
+ if (IS_ERR(v->balloon_thread))
+ goto out_free_vq;
+
+ list_add(&v->list, &balloon_devices);
+ dev_printk(KERN_INFO, &v->vdev->dev, "registered\n");
+
+ return 0;
+
+out_free_vq:
+ vdev->config->del_vq(v->vq);
+out_free:
+ kfree(v);
+ return err;
+}
+
+static void balloon_remove(struct virtio_device *vdev)
+{
+ struct virtballoon *v = vdev->priv;
+
+ kthread_stop(v->balloon_thread);
+ vdev->config->del_vq(v->vq);
+ list_del(&v->list);
+ kfree(v);
+}
+
+static void balloon_config_changed(struct virtio_device *vdev)
+{
+ struct virtballoon *v = vdev->priv;
+ u32 target_nrpages;
+
+ __virtio_config_val(v->vdev, 0, &target_nrpages);
+ atomic_set(&v->target_nrpages, target_nrpages);
+ wake_up(&v->balloon_wait);
+ dprintk(&vdev->dev, "%s\n", __func__);
+}
+
+static struct virtio_driver virtio_balloon = {
+ .driver.name = KBUILD_MODNAME,
+ .driver.owner = THIS_MODULE,
+ .id_table = id_table,
+ .probe = balloon_probe,
+ .remove = __devexit_p(balloon_remove),
+ .config_changed = balloon_config_changed,
+};
+
+module_param(kvm_balloon_debug, int, 0);
+
+static int __init kvm_balloon_init(void)
+{
+ return register_virtio_driver(&virtio_balloon);
+}
+
+static void __exit kvm_balloon_exit(void)
+{
+ struct virtballoon *v;
+
+ list_for_each_entry(v, &balloon_devices, list) {
+ while (v->balloon_size) {
+ DEFINE_WAIT(wait);
+
+ atomic_add(v->balloon_size, &v->target_nrpages);
+ wake_up(&v->balloon_wait);
+ prepare_to_wait(&v->rmmod_wait, &wait,
+ TASK_INTERRUPTIBLE);
+ schedule_timeout(HZ*10);
+ finish_wait(&v->rmmod_wait, &wait);
+ }
+ }
+
+ unregister_virtio_driver(&virtio_balloon);
+}
+
+module_init(kvm_balloon_init);
+module_exit(kvm_balloon_exit);
Index: linux-2.6-nv/drivers/virtio/virtio_pci.c
===================================================================
--- linux-2.6-nv.orig/drivers/virtio/virtio_pci.c
+++ linux-2.6-nv/drivers/virtio/virtio_pci.c
@@ -67,6 +67,7 @@ static struct pci_device_id virtio_pci_i
{ 0x1AF4, 0x1000, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Dummy entry */
{ 0x1AF4, 0x1001, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Dummy entry */
{ 0x1AF4, 0x1002, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Dummy entry */
+ { 0x1AF4, 0x1003, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Balloon */
{ 0 },
};
Index: linux-2.6-nv/include/linux/virtio_balloon.h
===================================================================
--- /dev/null
+++ linux-2.6-nv/include/linux/virtio_balloon.h
@@ -0,0 +1,20 @@
+#ifndef _LINUX_VIRTIO_BALLOON_H
+#define _LINUX_VIRTIO_BALLOON_H
+#include <linux/virtio_config.h>
+
+#define VIRTIO_ID_BALLOON 3
+
+#define CMD_BALLOON_INFLATE 0x1
+#define CMD_BALLOON_DEFLATE 0x2
+
+struct virtio_balloon_hdr {
+ __u8 cmd;
+ __u8 status;
+};
+
+struct virtio_balloon_config
+{
+ __u32 target_nrpages;
+};
+
+#endif /* _LINUX_VIRTIO_BALLOON_H */
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