RE: Can a task on each of 2 processors share 7 GB of physical m emory
RE: Can a task on each of 2 processors share 7 GB of physical m emory
- Subject: RE: Can a task on each of 2 processors share 7 GB of physical m emory
- From: "Miller, Larry" <email@hidden>
- Date: Fri, 14 Nov 2003 17:21:09 -0800
It is not clear to me that mmap(2) can let a process get a pointer to a
block of physical memory which has been previously wired and contains data
that has been loaded oby a PCI-X card.
It would be good if after suitable initialization, a file descriptor could
refer to say a 7 GB file that is mapped entirely into pages in physical
memory. The PCI-X card could load the data into those pages. And then a
process on each of the two processord could access whatever part of it they
wanted using mmap.
Is this possible???
Larry
-----Original Message-----
From: Jim Magee [
mailto:email@hidden]
Sent: Friday, November 14, 2003 4:17 PM
To: Miller, Larry
Cc: '''email@hidden' ' '
Subject: Re: Can a task on each of 2 processors share 7 GB of physical m
emory
mmap(2)?
On Nov 13, 2003, at 11:22 PM, Miller, Larry wrote:
>
Jim,
>
>
What would be an efficient remapping technique so a given task can
>
quickly
>
get a window into a desired part of the physical memory?
>
>
Larry
>
>
>
>
-----Original Message-----
>
From: Jim Magee
>
To: Miller, Larry
>
Cc: ''email@hidden' '
>
Sent: 11/13/2003 5:37 PM
>
Subject: Re: Can a task on each of 2 processors share 7 GB of
>
physical m
>
emory
>
>
On Nov 13, 2003, at 11:58 AM, Miller, Larry wrote:
>
> By wired, I mean the data that I put in the memory remains at a fixed
>
> place
>
> in physical memory - it is not paged out. This would probably be
>
> equivalent
>
> to a fixed mapping from VM to physical memory.
>
>
Then you probably could simultaneously wire 7GB out of 8GB physical as
>
you request.
>
>
> I heard that OS-X Panther was in some ways a 64-bit OS. In other
>
> words, I
>
> thought tasks could execute 64-bit addressing load and store machine
>
> instructions. Maybe I am mistaken.
>
>
>
> Also, I maybe mistakenly thought that you could compile a C/C++
>
> program in a
>
> way such that you could have 64-bit pointers that are dereferenced.
>
>
There are lots of things that define a 64-bit support. Using 64-bit
>
addresses to access >4GB of mapped virtual memory in a single task is
>
only one (maybe two - depends upon how you count) such feature (which
>
happens to be absent in Panther/Darwin 7.x). The ability to access
>
> 4GB of physical of physical memory in the first place is also one. An
>
>
additional feature is the ability to access and use 64-bit wide
>
registers in critical functions (and have the kernel preserve that
>
state correctly on interrupts/signals, etc...). These last two ARE in
>
Darwin 7.x.
>
>
> If these things are not available, does anyone one have an idea of
>
> when they
>
> will become available in the future?
>
>
As always, we can't make any statements about future Mac OS X plans
>
here or elsewhere. But from a technology point of view, it is
>
down-right inevitable that 64-bit address space support will make it
>
into Darwin - eventually.
>
>
In the meantime, using multiple address spaces to wire the memory down
>
in, and (re)mapping techniques to gain access to some percentage of the
>
memory at any given time, should work. For most applications, this
>
should be acceptable (performance-wise). It's the cost of getting stuff
>
in and out of physical memory that is the real bottleneck. At first
>
reading, this seems to fit well with the "up to 256MB chunk" model of
>
memory allocation you suggested earlier.
>
>
--Jim
>
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