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SubjectRe: Frontswap [PATCH 0/4] (was Transcendent Memory): overview
On 04/28/2010 08:55 AM, Pavel Machek wrote:
>> 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.
> wtf? So lets fix the ballooning driver instead?

You can't have a negative balloon size. The two models are not equivalent.

Balloon allows you to give up a page for which you have a struct page.
Frontswap (and swap) allows you to gain a page for which you don't have
a struct page, but you can't access it directly. The similarity is that
in both cases the host may want the guest to give up a page, but cannot
force it.

> There's no reason it could not be as fast as frontswap, right?
> Actually I'd expect it to be faster -- it can deal with big chunks.

There's no reason for swapping and ballooning to behave differently when
swap backing storage is RAM (they probably do now since swap was tuned
for disks, not flash, but that's a bug if it's true).

I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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