James Knott wrote:
While I don't have the exact details of PAE, in general memory mapping works by mapping physical memory outside of the normal addressing range, to an address within that range. This means that only a portion of that physical address range can be visible at a given time. An application has to be able to tell the operating system what portion of the physical memory it wants and also where in address space it wants it to be located.
Err, no. In Linux and many other OSes with virtual memory, no application needs to "tell the operating system what portion of the physical memory it wants" nor "where in address space it wants it to be located.". It only needs to say HOW MUCH it wants, and the virtual memory manager takes care of the rest. Here's an example of why your application does not need to know about PAE. When you install a SUSE 10.1 system on your machine with 1Gb RAM (for instance), you can pick e.g. the default kernel and no doubt your system and your applications will run fine. Then you add some more RAM - let's say you now have 8Gb RAM. To make use of this, you now install the bigsmp kernel or alternatively you just rebuild your current kernel with the CONFIG_HIGHMEM64G option enabled. Your applications aren't touched, yet they run just fine - but of course you can now run a lot more of them. They don't need to know about how much memory your system has, nor how it is accessed - again, the virtual memory manager takes care of that. Another example - I typically build applications on systems with a lot less memory than my servers. Maybe 512M, maybe 1Gb. So definitely without PAE. But these applications run fine on my servers with a lot more memory, without knowing anything about it. After all, their address space has not changed. It's still 4Gb per process, perhaps with a 3Gb/1Gb split for user/kernel. /Per Jessen, Zürich -- Check the headers for your unsubscription address For additional commands send e-mail to suse-linux-e-help@suse.com Also check the archives at http://lists.suse.com Please read the FAQs: suse-linux-e-faq@suse.com