On 09/28/2010 08:19 AM, Dave Young wrote:
Balloon could cause guest memory oom killing and panic. If we disable the oom killer it will be better at least avoid guest panic.
If alloc failed we can just adjust the balloon target to be equal to current number by call vdev->config->set
But during test I found the config->set num_pages does not change the config actually, Should I do hacks in userspace as well? If so where should I start to hack?
The guest is not supposed to set the target field in it's config. This
is a host read/write, guest read-only field.
The problem with your approach generally speaking is that it's unclear
whether this is the right policy. For instance, what if another
application held a very large allocation which caused the fill request
to stop but then shortly afterwards, the aforementioned application
released that allocation. If instead of just stopping, we paused and
tried again later, we could potentially succeed.
I think a better approach might be a graceful back off. For instance,
when you hit this condition, deflate the balloon by 10% based on the
assumption that you probably already gone too far. Before you attempt
to allocate to the target again, set a timeout that increases in
duration exponentially until you reach some maximum (say 10s).
This isn't the only approach, but hopefully it conveys the idea of
gracefully backing off without really giving up.
Regards,
Anthony Liguori
Thanks
--- linux-2.6.orig/drivers/virtio/virtio_balloon.c 2010-09-25 20:58:14.190000001 +0800
+++ linux-2.6/drivers/virtio/virtio_balloon.c 2010-09-28 21:05:42.203333675 +0800
@@ -25,6 +25,7 @@
#include<linux/freezer.h>
#include<linux/delay.h>
#include<linux/slab.h>
+#include<linux/oom.h>
struct virtio_balloon
{
@@ -97,8 +98,22 @@ static void tell_host(struct virtio_ball
wait_for_completion(&vb->acked);
}
-static void fill_balloon(struct virtio_balloon *vb, size_t num)
+static int cblimit(int times)
{
+ static int t;
+
+ if (t< times)
+ t++;
+ else
+ t = 0;
+
+ return !t;
+}
+
+static int fill_balloon(struct virtio_balloon *vb, size_t num)
+{
+ int ret = 0;
+
/* We can only do one array worth at a time. */
num = min(num, ARRAY_SIZE(vb->pfns));
@@ -106,10 +121,13 @@ static void fill_balloon(struct virtio_b
struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
__GFP_NOMEMALLOC | __GFP_NOWARN);
if (!page) {
- if (printk_ratelimit())
+ if (cblimit(5)) {
dev_printk(KERN_INFO,&vb->vdev->dev,
"Out of puff! Can't get %zu pages\n",
num);
+ ret = -ENOMEM;
+ goto out;
+ }
/* Sleep for at least 1/5 of a second before retry. */
msleep(200);
break;
@@ -120,11 +138,11 @@ static void fill_balloon(struct virtio_b
list_add(&page->lru,&vb->pages);
}
- /* Didn't get any? Oh well. */
- if (vb->num_pfns == 0)
- return;
+out:
+ if (vb->num_pfns)
+ tell_host(vb, vb->inflate_vq);
- tell_host(vb, vb->inflate_vq);
+ return ret;
}
static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
@@ -251,6 +269,14 @@ static void update_balloon_size(struct v
&actual, sizeof(actual));
}
+static void update_balloon_target(struct virtio_balloon *vb)
+{
+ __le32 num_pages = cpu_to_le32(vb->num_pages);
+ vb->vdev->config->set(vb->vdev,
+ offsetof(struct virtio_balloon_config, num_pages),
+ &num_pages, sizeof(num_pages));
+}
+
static int balloon(void *_vballoon)
{
struct virtio_balloon *vb = _vballoon;
@@ -267,9 +293,14 @@ static int balloon(void *_vballoon)
|| freezing(current));
if (vb->need_stats_update)
stats_handle_request(vb);
- if (diff> 0)
- fill_balloon(vb, diff);
- else if (diff< 0)
+ if (diff> 0) {
+ int oom;
+ oom_killer_disable();
+ oom = fill_balloon(vb, diff);
+ oom_killer_enable();
+ if (oom)
+ update_balloon_target(vb);
+ } else if (diff< 0)
leak_balloon(vb, -diff);
update_balloon_size(vb);
}
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