This trivial patch never did manage to find its way
in.  Marcelo called it to my attention earlier in
the week.  I've tweaked it to apply to kvm-83 and
the resulting patch is attached.  I've left the
prior e-mail discussion below for reference.

-john


john cooper wrote:
> This patch from over a month ago doesn't seem to have
> made it into kvm-73 and may have been lost in the
> shuffle.  Attached is essentially the same patch but
> as applied to kvm-73, and validated relative to that
> version.
> 
> In a nutshell the intention here is to allow
> preallocation of guest huge page backed memory at
> qemu initialization time to avoid a quirk in the
> kernel's huge page accounting allowing overcommit
> of huge pages.  Failure of the kernel to resolve a
> guest fault to overcommitted huge page memory during
> runtime results in sigkill termination of the guest.
> This patch provides the option of avoiding such
> behavior at the cost of up-front preallocation of
> physical huge pages backing the guest.
> 
> -john
> 
> 
> Anthony Liguori wrote:
>> john cooper wrote:
>>> Anthony Liguori wrote:
>>>> john cooper wrote:
>>>>> As it currently exists alloc_hpage_mem() is tied to
>>>>> the notion of huge page allocation as it will reference
>>>>> gethugepagesize() irrespective of *mem_path.  So even
>>>>> in the case of tmpfs backed files, if the host kernel
>>>>> has been configured with CONFIG_HUGETLBFS we will wind
>>>>> up doing allocations of /dev/shm mapped files at
>>>>> /proc/meminfo:Hugepagesize granularity.
>>>>
>>>> Which is fine.  It just means we round -m values up to even numbers.
>>>
>>> Well, yes it will round the allocation.  But from a
>>> minimally sufficient 4KB boundary to that of 4MB/2MB
>>> relative to a 32/64 bit x86 host which is excessive.
>>>
>>>>> Probably not what was intended but probably not too
>>>>> much of a concern as "-mem-path /dev/shm" is likely
>>>>> only used in debug of this flag and associated logic.
>>>>> I don't see it currently being worth the trouble to
>>>>> correct from a squeaky clean POV, and doing so may
>>>>> drag in far more than the header file we've just
>>>>> booted above to deal with this architecture/config
>>>>> dependency.
>>>>
>>>> Renaming a function to a name that's less accurate seems bad to me.  
>>>> I don't mean to be pedantic, but it seems like a strange thing to 
>>>> do.  I prefer it the way it was before.
>>>
>>> I don't see any harm reverting the name.  But I do
>>> believe it is largely cosmetic as given the above,
>>> the current code does require some work to make it
>>> independent of huge page assumptions.  Update attached.
>>>
>>> -john
>>
>> Looks good to me.
>>
>> Acked-by: Anthony Liguori <aliguori@us.ibm.com>
>>
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> 
> 


-- 
john.cooper@third-harmonic.com