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

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Message-ID: <4BD3377E.6010303@redhat.com>
Date:	Sat, 24 Apr 2010 21:25:02 +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 04/23/2010 07:26 PM, Dan Magenheimer wrote:
>>
>> Looks like "init" == open, "put_page" == write, "get_page" == read,
>> "flush_page|flush_area" == trim.  The only difference seems to be that
>> an overwriting put_page may fail.  Doesn't seem to be much of a win,
>>      
> No, ANY put_page can fail, and this is a critical part of the API
> that provides all of the flexibility for the hypervisor and all
> the guests. (See previous reply.)
>    

The guest isn't required to do any put_page()s.  It can issue lots of 
them when memory is available, and keep them in the hypervisor forever.  
Failing new put_page()s isn't enough for a dynamic system, you need to 
be able to force the guest to give up some of its tmem.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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