[RFC][Patch v12 2/2] virtio-balloon: interface to support free page reporting

Nitesh Narayan Lal
2019-08-12T13:13:20Z

Enables the kernel to negotiate VIRTIO_BALLOON_F_REPORTING feature with
the host. If it is available and page_reporting_flag is set to true,
page_reporting is enabled and its callback is configured along with
the max_pages count which indicates the maximum number of pages that
can be isolated and reported at a time. Currently, only free pages of
order >= (MAX_ORDER - 2) are reported. To prevent any false OOM
max_pages count is set to 16.

By default page_reporting feature is enabled and gets loaded as soon
as the virtio-balloon driver is loaded. However, it could be disabled
by writing the page_reporting_flag which is a virtio-balloon parameter.

Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
---
drivers/virtio/Kconfig | 1 +
drivers/virtio/virtio_balloon.c | 64 ++++++++++++++++++++++++++++-
include/uapi/linux/virtio_balloon.h | 1 +
3 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 078615cf2afc..4b2dd8259ff5 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -58,6 +58,7 @@ config VIRTIO_BALLOON
tristate "Virtio balloon driver"
depends on VIRTIO
select MEMORY_BALLOON
+ select PAGE_REPORTING
---help---
This driver supports increasing and decreasing the amount
of memory within a KVM guest.
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 226fbb995fb0..defec00d4ee2 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -19,6 +19,7 @@
#include <linux/mount.h>
#include <linux/magic.h>
#include <linux/pseudo_fs.h>
+#include <linux/page_reporting.h>

/*
* Balloon device works in 4K page units. So each page is pointed to by
@@ -46,6 +47,7 @@ enum virtio_balloon_vq {
VIRTIO_BALLOON_VQ_DEFLATE,
VIRTIO_BALLOON_VQ_STATS,
VIRTIO_BALLOON_VQ_FREE_PAGE,
+ VIRTIO_BALLOON_VQ_REPORTING,
VIRTIO_BALLOON_VQ_MAX
};

@@ -55,7 +57,8 @@ enum virtio_balloon_config_read {

struct virtio_balloon {
struct virtio_device *vdev;
- struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
+ struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq,
+ *reporting_vq;

/* Balloon's own wq for cpu-intensive work items */
struct workqueue_struct *balloon_wq;
@@ -113,6 +116,9 @@ struct virtio_balloon {

/* To register a shrinker to shrink memory upon memory pressure */
struct shrinker shrinker;
+
+ /* To configure page reporting to report isolated pages */
+ struct page_reporting_config page_reporting_conf;
};

static struct virtio_device_id id_table[] = {
@@ -120,6 +126,10 @@ static struct virtio_device_id id_table[] = {
{ 0 },
};

+bool page_reporting_flag = true;
+module_param(page_reporting_flag, bool, 0644);
+MODULE_PARM_DESC(page_reporting_flag, "Enable page reporting");
+
static u32 page_to_balloon_pfn(struct page *page)
{
unsigned long pfn = page_to_pfn(page);
@@ -152,6 +162,44 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)

}

+void virtballoon_report_pages(struct page_reporting_config *page_reporting_conf,
+ unsigned int num_pages)
+{
+ struct virtio_balloon *vb = container_of(page_reporting_conf,
+ struct virtio_balloon,
+ page_reporting_conf);
+ struct virtqueue *vq = vb->reporting_vq;
+ int err, unused;
+
+ /* We should always be able to add these buffers to an empty queue. */
+ err = virtqueue_add_inbuf(vq, page_reporting_conf->sg, num_pages, vb,
+ GFP_NOWAIT);
+ /* We should not report if the guest is low on memory */
+ if (unlikely(err))
+ return;
+ virtqueue_kick(vq);
+
+ /* When host has read buffer, this completes via balloon_ack */
+ wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+}
+
+static void virtballoon_page_reporting_setup(struct virtio_balloon *vb)
+{
+ struct device *dev = &vb->vdev->dev;
+ int err;
+
+ vb->page_reporting_conf.report = virtballoon_report_pages;
+ vb->page_reporting_conf.max_pages = PAGE_REPORTING_MAX_PAGES;
+ err = page_reporting_enable(&vb->page_reporting_conf);
+ if (err < 0) {
+ dev_err(dev, "Failed to enable reporting, err = %d\n", err);
+ page_reporting_flag = false;
+ vb->page_reporting_conf.report = NULL;
+ vb->page_reporting_conf.max_pages = 0;
+ return;
+ }
+}
+
static void set_page_pfns(struct virtio_balloon *vb,
__virtio32 pfns[], struct page *page)
{
@@ -476,6 +524,7 @@ static int init_vqs(struct virtio_balloon *vb)
names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
names[VIRTIO_BALLOON_VQ_STATS] = NULL;
names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+ names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;

if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
names[VIRTIO_BALLOON_VQ_STATS] = "stats";
@@ -487,11 +536,18 @@ static int init_vqs(struct virtio_balloon *vb)
callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
}

+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+ names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
+ callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
+ }
err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
vqs, callbacks, names, NULL, NULL);
if (err)
return err;

+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+ vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
+
vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
@@ -924,6 +980,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
if (err)
goto out_del_balloon_wq;
}
+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING) &&
+ page_reporting_flag)
+ virtballoon_page_reporting_setup(vb);
virtio_device_ready(vdev);

if (towards_target(vb))
@@ -971,6 +1030,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
destroy_workqueue(vb->balloon_wq);
}

+ if (page_reporting_flag)
+ page_reporting_disable(&vb->page_reporting_conf);
remove_common(vb);
#ifdef CONFIG_BALLOON_COMPACTION
if (vb->vb_dev_info.inode)
@@ -1027,6 +1088,7 @@ static unsigned int features[] = {
VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
VIRTIO_BALLOON_F_FREE_PAGE_HINT,
VIRTIO_BALLOON_F_PAGE_POISON,
+ VIRTIO_BALLOON_F_REPORTING,
};

static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index a1966cd7b677..19974392d324 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -36,6 +36,7 @@
#define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
#define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */
#define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */
+#define VIRTIO_BALLOON_F_REPORTING 5 /* Page reporting virtqueue */

/* Size of a PFN in the balloon interface. */
#define VIRTIO_BALLOON_PFN_SHIFT 12
--
2.21.0