Re: [PATCH 0/4] Swapping

[Izik Eidus <izike-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Izik Eidus wrote:
> Anthony Liguori wrote:
>> Izik Eidus wrote:
>>> this patchs allow the guest not shadowed memory to be swapped out.
>>>
>>> to make it the must effective you should run -kvm-shadow-memory 1 
>>> (witch will make your machine slow)
>>> with -kvm-shadow-memory 1,  3giga memory guest can get to be just 
>>> 32mb on physical host!
>>>
>>> when not using -kvm-shadow-memory, i saw 4100mb machine getting to 
>>> as low as 168mb on the physical host (not as bad as i thought it 
>>> would be, and surely not as bad as it can be with 41mb of shadow 
>>> pages :))
>>>   
>>
>> So what exactly does this option do?  Is it really worth exposing it 
>> as an option if it slows down guests so much?
>>
>> At least, a better name for the option would be nice.
>>
>> Regards,
>>
>> Anthony Liguori
> -kvm-shadow-memory was included in kvm from version 46.
> it control how much pages will be allocated to the shadow cache, (from 
> version 46 the default is 2% of the system (so 4.1giga have about 80 
> mbs of shadow cache by default))
> the problem is that each page that present at the shadow cache ( mmu 
> pages ) cant be swapped out, so as lower as the number of shadow 
> caches you have as more swappable will be
> useful.
>
> (this option (kvm-shadow-memory) was included to make it possible that 
> as less as possible shadow cache memory will be deleated ( beacuse it 
> have big overhead to lose this cache)
>
just to make it clearer,
-kvm-shadow-memory main purpose is to speed up the guest, ( as more mmu 
pages you have to the shadow cache, as faster as your guest will be while
it working with alot of memory)
(the main mission is that kvm_free_some_pages() will get called as less 
as possible)


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