Re: [RFC] transcendent memory for Linux
From: Avi Kivity
Date: Sun Jun 28 2009 - 03:42:24 EST
On 06/27/2009 04:18 PM, Linus Walleij wrote:
2009/6/20 Dan Magenheimer<dan.magenheimer@xxxxxxxxxx>:
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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