Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

[Avi Kivity <avi@redhat.com>]

On 04/25/2010 04:12 PM, Dan Magenheimer wrote:
>>
>> In this case you could use the same mechanism to stop new put_page()s?
>>      
> You are suggesting the hypervisor communicate dynamically-rapidly-changing
> physical memory availability information to a userland daemon in each guest,
> and each daemon communicate this information to each respective kernel
> to notify the kernel that hypervisor memory is not available?
>
> Seems very convoluted to me, and anyway it doesn't eliminate the need
> for a hook placed exactly where the frontswap_put hook is placed.
>    

Yeah, it's pretty ugly.  Balloons typically communicate without a daemon 
too.

>> Seems frontswap is like a reverse balloon, where the balloon is in
>> hypervisor space instead of the guest space.
>>      
> That's a reasonable analogy.  Frontswap serves nicely as an
> emergency safety valve when a guest has given up (too) much of
> its memory via ballooning but unexpectedly has an urgent need
> that can't be serviced quickly enough by the balloon driver.
>    

(or ordinary swap)

-- 
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