From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 5B7186B004D for ; Sun, 28 Jun 2009 03:40:25 -0400 (EDT) Message-ID: <4A471F01.7010400@redhat.com> Date: Sun, 28 Jun 2009 10:42:57 +0300 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [RFC] transcendent memory for Linux References: <63386a3d0906270618h5be01265v759f5acd1f49682f@mail.gmail.com> In-Reply-To: <63386a3d0906270618h5be01265v759f5acd1f49682f@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Linus Walleij Cc: Dan Magenheimer , linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, npiggin@suse.de, chris.mason@oracle.com, kurt.hackel@oracle.com, dave.mccracken@oracle.com, jeremy@goop.org, Rik van Riel , alan@lxorguk.ukuu.org.uk, Rusty Russell , Martin Schwidefsky , akpm@osdl.org, Marcelo Tosatti , Balbir Singh , tmem-devel@oss.oracle.com, sunil.mushran@oracle.com, linux-mm@kvack.org, Himanshu Raj , linux-embedded@vger.kernel.org List-ID: On 06/27/2009 04:18 PM, Linus Walleij wrote: > 2009/6/20 Dan Magenheimer: > > >> 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org