On Thu, Aug 09, 2007 at 11:23:09AM +0300, Ira Abramov wrote: > the problem I am having is the PCI memory mapping. It's set at > "2.5GB" by default in the BIOS, and Debian Etch comes up and indeed > sees only 2.5GB. I have set it up to 3.5G to lose less RAM, but I > would still like to use the rest of the RAM! I tried booting with > ram=4G but still the kernel sees only 3.5. I guess I need to use > memmap= as well, but I don't have that information. > > the only clue is this tiny line in the BIOS docs: > > -PAE mode and the equivalent Linux mode must be set to see > > 2.5GB of memory. > > but running the debian "bigmem" kernel with 4G or less has an > unwanted penalty on speed, doesn't it?
For all intents and purposes, you have more than 4G of RAM. More accurately, some of your RAM is only addressable using addresses that are over 4G. The reason why is that your physical memory addresses look like this (simplified): 0<---RAM--->3.5G<---PCI HOLE---><---more RAM over 4G---> Because some PCI devices cannot deal with addresses over 4G. To be able to map the RAM that has physical address over 4G in the CPU's page tables, you need a PAE kernel. As for the penalty on speed, I doubt you'll be able to measure it, and it will be offset by the extra RAM. Cheers, Muli ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
