Messages in this thread | | | Date | Wed, 18 Aug 2004 11:59:42 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: Help with mapping memory into kernel space? |
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On Wed, 18 Aug 2004, Daniel Gryniewicz wrote:
> On Tue, 2004-08-17 at 22:39 -0700, Brian McGrew wrote: > > Good day All: > > > > <snip> > > > The overall problem is that the more system memory we install, > > the fewer IBB's we can use. For instance, 256MB lets us use > > four IBB's; 512MB lets us use three IBB's and so on. Basicly, > > the kernel blows up trying to map memory. Each IBB has two > > banks of 64MB of RAM on them which we try and memmap to system > > memory for speed of addressing. So essentaily, we're sending > > out four camera systems with only 256MB of memory which is only > > about one quarter of what we need. > > On x86, the kernel has 1 GiB of address space. Try the 2G/2G split > patches, or the 4G/4G patches, either one of which should increase your > kernel address space enough to map both memory and your buffers. > > Daniel
> out four camera systems with only 256MB of memory which is only ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
You can use as much memory as you can afford if the designer of this system would only understand that you can't fit 4 GB of application RAM into 4 GB of address-space and leave anything available for the system.
It needs to be done like this:
------------|-------------|----------- Other | N Mbyte | Other address space address | window | .................. ------------|-------------|----------- | | ----------------- | Page register | |---------------- | ----------------------- | Page 0 | |--|-------------------- | Page 1 | |--------------------- Page N, etc.
You make a small window in the available address-space, and you map your RAM into that address-space with a page register. You can access much, much more RAM than available address-space, and with things like video and pictures, the occasional switching of a page-register adds practically no overhead.
Cheers, Dick Johnson Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips). Note 96.31% of all statistics are fiction.
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