linux-kernel - Re: [RFC] transcendent memory for Linux

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Message-ID: <4A471F01.7010400@redhat.com>
Date:	Sun, 28 Jun 2009 10:42:57 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Linus Walleij <linus.ml.walleij@...il.com>
CC:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	npiggin@...e.de, chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, jeremy@...p.org,
	Rik van Riel <riel@...hat.com>, alan@...rguk.ukuu.org.uk,
	Rusty Russell <rusty@...tcorp.com.au>,
	Martin Schwidefsky <schwidefsky@...ibm.com>, akpm@...l.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	tmem-devel@....oracle.com, sunil.mushran@...cle.com,
	linux-mm@...ck.org, Himanshu Raj <rhim@...rosoft.com>,
	linux-embedded@...r.kernel.org
Subject: Re: [RFC] transcendent memory for Linux

On 06/27/2009 04:18 PM, Linus Walleij wrote:
> 2009/6/20 Dan Magenheimer<dan.magenheimer@...cle.com>:
>
>    
>> We call this latter class "transcendent memory" and it
>> provides an interesting opportunity to more efficiently
>> utilize RAM in a virtualized environment.  However this
>> "memory but not really memory" may also have applications
>> in NON-virtualized environments, such as hotplug-memory
>> deletion, SSDs, and page cache compression.  Others have
>> suggested ideas such as allowing use of highmem memory
>> without a highmem kernel, or use of spare video memory.
>>      
>
> Here is what I consider may be a use case from the embedded
> world: we have to save power as much as possible, so we need
> to shut off entire banks of memory.
>
> Currently people do things like put memory into self-refresh
> and then sleep, but for long lapses of time you would
> want to compress memory towards lower addresses and
> turn as many banks as possible off.
>
> So we have something like 4x16MB banks of RAM = 64MB RAM,
> and the most necessary stuff easily fits in one of them.
> If we can shut down 3x16MB we save 3 x power supply of the
> RAMs.
>
> However in embedded we don't have any swap, so we'd need
> some call that would attempt to remove a memory by paging
> out code and data that has been demand-paged in
> from the FS but no dirty pages, these should instead be
> moved down to memory which will be retained, and the
> call should fail if we didn't succeed to migrate all
> dirty pages.
>
> Would this be possible with transcendent memory?
>    

You could do this with memory defragmentation, which is needed for 
things like memory hotunplug ayway.

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

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