[Xen-devel] Re: xc: error: xc_machphys_mfn_list: 83 != 129 when suspending 32GB PV DomU

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 11/03/2011 18:52, "Gianni Tedesco" <gianni.tedesco@xxxxxxxxxx> wrote:

> Further debugging reveals the variables are set as such:
>  (XEN) compat_machine_to_phys_mapping = 18446606377058041856
>  (XEN) max_page = 67272704
>  (XEN) MACH2PHYS_COMPAT_NR_ENTRIES(current->domain) = 43515904
>  (XEN) RDWR_COMPAT_MPT_VIRT_START = 18446606377058041856
>  (XEN) RDWR_COMPAT_MPT_VIRT_END = 18446606378131783680
>  (XEN) limit = 18446606377232105472, (1 << L2_PAGETABLE_SHIFT) = 2097152
> 
> Could it be that the compat mach-to-phys conversion table size of 1GB is
> too small?

It is insufficient to cover all of the system's memory. The reason for the
limit is that a 1GB M2P table is all that is reasonable to map into a 32-bit
domain's address space while still leaving space for the guest's own
mappings.

We could make the compat m2p bigger solely for mapping by dom0 when doing
save/restore? However, you'd likely still soon hit the mmap limit for the
save/restore process in dom0. It might extend the lifetime of your 32-bit
dom0 for a bit longer however. Long enough for the lightweight HVM container
for PV guests work to get checked in and make our PV 64-bit guest
performance better.

 -- Keir

> Or that there exists some other arbitrary limit on the size
> of domains that can be suspended [when using a 32bit dom0] ?



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