Re: [Qemu-devel] [PATCH qemu v4 09/18] memory: Store physical root MR in FlatView

[Alexey Kardashevskiy]

On 21/09/17 15:22, Alexey Kardashevskiy wrote:
> On 21/09/17 10:02, Alexey Kardashevskiy wrote:
>> On 21/09/17 03:15, Paolo Bonzini wrote:
>>> On 20/09/2017 13:46, Alexey Kardashevskiy wrote:
>>>> Address spaces get to keep a root MR (alias or not) but FlatView stores
>>>> the actual MR as this is going to be used later on to decide whether to
>>>> share a particular FlatView or not.
>>>>
>>>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>>>> ---
>>>> Changes:
>>>> v4:
>>>> * s/memory_region_unalias_entire/memory_region_get_flatview_root/
>>>
>>> Did you try the idea of checking for single-child regions too?
>>
>> No, I did not, I do not see how I can actually measure the difference - the
>> PCI and virtio root MRs or single child MRs are unique anyway, I can save
>> some time by just checking for 2 @enabled flags instead of rendering a
>> FlatView but rendering such cases itself is fast as well. I'll give a try
>> though.
> 
> I tried. memory_region_get_flatview_root() returns a last child which still
> covers the same space as the root; generate_memory_topology() checks for
> @enabled first and only if it is enabled - renders a new FV (this solves
> PCI busmater).
> 
> With 256 CPUs and 256 virtio devices this saves 0.1s (20.4s -> 20.3s) and
> 100MB of RAM (14.38G -> 14.28G) :) I'll push it out anyway.


Hm. Actually using that child as a root for FV in 09/18 increases memory
use from 18G to 20G. If I just check the nested MR if it is not enabled,
this does not change a thing - time and memory use is the same. Well, it is
beyond accuracy of my measurements :)


-- 
Alexey