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

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Message-ID: <4BD4413D.5030808@redhat.com>
Date:	Sun, 25 Apr 2010 16:18:53 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	hugh.dickins@...cali.co.uk, ngupta@...are.org, JBeulich@...ell.com,
	chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, npiggin@...e.de,
	akpm@...ux-foundation.org, riel@...hat.com
Subject: Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

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)

-- 
error compiling committee.c: too many arguments to function

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