Re: [PATCH 0/4] Swapping

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Izik Eidus wrote:
> 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)

Yeah, I realized what -kvm-shadow-memory shortly after I sent my first 
note :-)  Sorry for the noise.

Regards,

Anthony Liguori


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