[Xen-bugs] [Bug 651] New: kernel panic when set dom0 to value less than 1 to 2 % of host mem

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=651

           Summary: kernel panic when set dom0 to value less than 1 to 2 %
                    of host mem
           Product: Xen
           Version: unstable
          Platform: x86-64
        OS/Version: Linux-2.6
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Hypervisor
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: krysans@xxxxxxxxxx
                CC: aravindh.puthiyaparambil@xxxxxxxxxx


Running on Unisys ES7000/one with 16 GB of RAM; dom0 is allocated almost all of
the memory.  I issued xm mem-set 0 256 to decrease dom0's memory to 256 MB. 
Using xentop, I see the amount of memory allocated to dom0 slowly decrease.   
Using SLES10 Beta 11 upgraded to xen changeset 9994. The serial console output
indicates out of memory condition and is attached.  

In devel list, Keir indicated:
I don't think this behaviour is surprising. The kernel is probably 
taking about 1% of memory to track memory usage. So trying to balloon 
down to 1-2% of your initial memory reservation is rather harsh.

The 'fix' here is to stop users being able to shoot their feet off, by 
setting a lower bound on ballooning that is related to the initial 
memory size of the guest, and/or quiesce the balloon driver when 
low-memory and out-of-memory code paths are executed in the guest.

Aravindh is looking into a fix for this and will send in a patch.


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