Re: [Qemu-devel] [PATCH qemu v4 18/18] memory: Give memory_region_transaction_commit a hint

[Alexey Kardashevskiy]

On 21/09/17 03:14, Paolo Bonzini wrote:
> On 20/09/2017 13:46, Alexey Kardashevskiy wrote:
>> This extends memory_region_transaction_commit() to receive a MR as
>> if it is a root MR or its topmost parent is, then we can only rebuild
>> its FlatView and update it for address spaces sharing it.
>>
>> The optimization gets disabled though if there is full update about to
>> commit.
>>
>> memory_region_set_enabled() is a special case here, it does not use
>> a hint when MR is being disabled.
>>
>> On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this brings
>> down the boot time from 20s to 12s, the total memory footprint
>> goes down (17G -> 8G).
> 
> I think this is incorrect if MR has an alias (no matter if enabling or
> disabling)?

Hmmm. Right. I can add a aliases_nr counter to an MR (it does not even have
to go down as aliases are not creared/destroyed often) and take the slow
path if it is not zero, does it make sense?


-- 
Alexey