On 2011-01-25 20:13, Alex Williamson wrote:
> On Tue, 2011-01-25 at 17:35 +0100, Jan Kiszka wrote:
>> On 2011-01-25 15:53, Avi Kivity wrote:
>>> On 01/25/2011 04:41 PM, Alex Williamson wrote:
>>>>> >
>>>>> >
>>>>> > kvm: Allow memory slot array to grow on demand
>>>>> >
>>>>> > Remove fixed KVM_MEMORY_SLOTS limit, allowing the slot array
>>>>> > to grow on demand. Private slots are now allocated at the
>>>>> > front instead of the end. Only x86 seems to use private slots,
>>>>>
>>>>> Hmm, doesn't current user space expect slots 8..11 to be the private
>>>>> ones and wouldn't it cause troubles if slots 0..3 are suddenly
>>>> reserved?
>>>>
>>>> The private slots aren't currently visible to userspace, they're
>>>> actually slots 32..35. The patch automatically increments user passed
>>>> slot ids so userspace has it's own zero-based view of the array.
>>>> Frankly, I don't understand why userspace reserves slots 8..11, is this
>>>> compatibility with older kernel implementations?
>>>
>>> I think so. I believe these kernel versions are too old now to matter,
>>> but of course I can't be sure.
>>
>> Will check and enable those 4 additional slots for user space if we no
>> longer need to exclude them.
>
> Appears that the history goes something like this...
>
> * Once upon a time we had 8 memory slots
>
> * v2.6.24-4949-ge0d62c7 added 4 reserved slots above those 8
>
> * v2.6.24-4950-gcbc9402 made use of slot 8 for tss
>
> * v2.6.24-4962-gf78e0e2 made use of slot 9 for tpr
>
> * v2.6.25-5341-gef2979b bumped the 8 slots to 32
>
> * v2.6.26-rc1-13-gb7ebfb0 made use of slot 10 for ept
>
> * v2.6.28-4952-g6fe6397 moved the previously hard coded slots
> 8,9,10 up to KVM_MEMORY_SLOTS + {0,1,2}
>
Nice overview!
> So we haven't needed to reserve 8..11 for a while and we've never made
> use of all 4 private slots. I should reduce that to 3 in my patch.
> Maybe there's a test we could do in userspace to figure out we don't
> have to skip those anymore?
We can simply remove the test, 2.6.29 is our entry barrier for both
upstream and qemu-kvm now.
Jan
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