Re: vballoon: page allocation failure. order:0 -> Kernel panic

[Avi Kivity <avi@redhat.com>]

Tomasz Chmielewski wrote:
> I'm trying to use ballooning with kvm-83.
>
> Although I'm able to limit the guest's memory, when I try to increase 
> it right after that, I get "vballoon: page allocation failure. 
> order:0" followed by a kernel panic.
>
> Is it expected?
>
> The guest is running Debian Lenny with 2.6.26 kernel. It had initially 
> 256 MB memory.
>

It's a guest bug, fixed in 2.6.27 by

commit 532a6086e35fa3b5761e68af36d4e42a550eba15
Author: Anthony Liguori <aliguori@us.ibm.com>
Date:   Mon Aug 18 17:15:31 2008 -0500

    virtio_balloon: fix towards_target when deflating balloon
   
    Both v and vb->num_pages are u32 and unsigned int respectively.  If 
v is less
    than vb->num_pages (and it is, when deflating the balloon), the 
result is a
    very large 32-bit number.  Since we're returning a s64, instead of 
getting the
    same negative number we desire, we get a very large positive number.
   
    This handles the case where v < vb->num_pages and ensures we get a 
small,
    negative, s64 as the result.
   
    Rusty: please push this for 2.6.27-rc4.  It's probably appropriate 
for the
    stable tree too as it will cause an unexpected OOM when ballooning.
   
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (simplified)

diff --git a/drivers/virtio/virtio_balloon.c 
b/drivers/virtio/virtio_balloon.c
index bfef604..62eab43 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -158,7 +158,7 @@ static inline s64 towards_target(struct 
virtio_balloon *vb)
        vb->vdev->config->get(vb->vdev,
                              offsetof(struct virtio_balloon_config, 
num_pages),
                              &v, sizeof(v));
-       return v - vb->num_pages;
+       return (s64)v - vb->num_pages;
 }
 
 static void update_balloon_size(struct virtio_balloon *vb)




-- 
error compiling committee.c: too many arguments to function