Description of problem:

In fact, I was doing virsh managedsave but that uses qemu's migration capabilities so I'll talk about migration from now on...

Migrating 8GB guest after boot works just fine. Then I modify guest's memory, e.g., using the following code:

#include <stdlib.h>
#define size 7900000000L

int main(void)
{
        char *ble = malloc(size);
        long long i;

        if (!ble)
                return -1;

        for (i = 0; i < size; i++)
                ble[i] = i & 0xff;

        return 0;
}

After this process finishes, the guest can no longer be migrated. Actually the migration doesn't even start and the following error is printed immediately:

error: operation failed: migration to 'exec:cat | { dd bs=4096 seek=1 if=/dev/null && dd bs=1048576; } 1<>/var/lib/libvirt/qemu/save//console.save' failed: migration failed

No message appears on qemu's stderr.

Version-Release number of selected component (if applicable):

kvm-83-205.el5
kernel-2.6.18-228.el5

How reproducible:

Everytime.

Steps to Reproduce:
1. start a guest with 8GB of memory
2. modify guest's memory
3. virsh managedsave
  
Actual results:

migration failed


Expected results:

guest saved successfully

Additional info:

The guest is RHEL-5.5